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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 39
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 40
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 41
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 42
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 43
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 44
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 45
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 46
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 47
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 48
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 49
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 50
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 51
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 52
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 53
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 54
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 55
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 56
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 57
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 58
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 59
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 60
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 61
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 62
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 63
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 64
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 65
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 66
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 67
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 68
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 69
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 70
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 71
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 72
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 73
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 74
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 75
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 76
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 77
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 78
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 79
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 80
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 81
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
×
Page 82
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 83
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 84
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 85
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 86
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 87
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 88
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 89
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 90
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 91
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 92
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 93
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 94
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 95
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 96
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 97
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 98
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 99
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 100
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 101
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 102
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 103
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 104
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Page 105
Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Suggested Citation:"MODE AND RATE OF HEAT TRANSFER IN CANNED MEATS." National Research Council. 1954. Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953. Washington, DC: The National Academies Press. doi: 10.17226/18630.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

any more. They can sit and argue about what they have been doing, take their hair down, and call each other names. When they come home from such a meeting, they will then be stimulated to further work; then they can meet before you and let you know what they have accomplished. To sum up, I would like to see more funds devoted to fundamental research and more funds devoted to these small confer- ences. They are extremely useful. CHAIRMAN ROBINSON Thank you very much, Dr. Halvorson. Now we come to another phase of this consideration of the quality and stability of canned meats. That has to do with the mode of heat transfer in canned meats, and our first speaker on that this afternoon will discuss "The Effect of Processing Temperature upon the Rate and Pattern of Heat Distribution within a Can of Beef." He is Dr. Tischer, formerly of Iowa State College, now director, Food Labora- tories, Quartermaster Food & Container Institute for the Armed Forces. The Effect of Processing Temperature upon the Rate and Pattern of Heal Distribution within a Can of Beef ROBERT G. TISCHER The work to be described was undertaken as part of a project designed to illustrate the effect of processing temperature, especial- ly in ranges higher than those usually employed in the processing of meat, on the ultimate quality of canned beef. The distribution of iso- thermal surfaces in the container during processing at various tem- peratures was studied to learn, if possible, the actual occurrences in beef and to discover whether these occurrences are identical with those predicted from theoretical considerations. Experimental procedure. The experimental design used contained 6 equally spaced processing temperatures ranging from 225° to 315° F. At each temperature a set of times was used appropriate for that temperature. The times at 225° F. ranged from 10 to 120 minutes; the times at 315° F. were 2 to 24 minutes and the times for the remaining temperatures were located between these 2 sets. The tem- perature points measured in the container were 25 in number and were measured at the rate of 7 per experimental unit. The placement of the points within the container is shown in Figure 1 indicating that the points were systematically placed on vertical axes of the can from the center toward the outside and covering most of the half-plane of the can. Measurements were made with a multipoint recording potentiometer. The processes were controlled with an automatic time- temperature program controller. Discussion The temperature curves derived for each point in the processes were interpo- lated by means of graphical methods to yield isothermal lines within the container. In a consideration of isotropic media heating by conduction, the normal theo- retical expectations for isothermals would begin with a cylindrical distribution at 38

FIGURE 1. PLACEMENT OF POINTS IN A CYLINDRI- CAL CONTAINER. TEMPERATURES WERE REPEATEDLY MEASURED AT THE POINTS SHOWN DURING EACH PROCESS AND FOR THE DURATION OF THE PROCESS. i 1 1 . 1 - i • V • • • « » » t 1 I • 4 • • • • • • i , 1/4* i , t t « 1.5* -^1 i time zero followed by ellipsoidal distributions as time progresses and ending in a small sphere or a true geometric point at some later time in the process. These occurrences are illustrated in Figure 2 in which the periphery of the half-plane of the can may be taken as a representative of the cylindrical distribution; the egg-shaped isothermal shell shown in the can represents one of the infinite number of the isothermal ellipsoids which might normally be expected. FIGURE 2. HALF-PLANE DIAGRAM OF A CYLINDRI- CAL ISOTHERMAL ELLIPSOID DISTRIBU- TION. FIGURE 3. ELLIPSOID ISOTHERMAL SHOWING CAR- DIOID TENDENCY AT LOWER END. 89

'~V > \/t II 193 V\, i ' ' " \ \« : V\\, ~ 20O-' "- 225 1 ------ 90 Mill. 235 L -* 243° F. 40min. I--. 1206 \\ 215 ' /,' 225^--__x' t 235L-- '* 24Q ~' 5Omin. I r~ ---- 227 \ 230- • 235k. '-^ / 24OJ-. FIGURE 4. DISTRIBUTION OP ISOTHERMAL LINES IN THE HALF PLANE OF A CONTAINER BEING PROCESSED AT 243° F. AT 4 TIMES; 20, 30, 40, AND 50 MINUTES. THIS FIGURE SHOWS THE AREAS OF SLOWEST HEATING FROM WHICH THE TORUS MAY BE DEVELOPED BY ROTA- TION THROUGH 360° F. AN ILLUSTRATION OF THIS DEVELOPMENT IS APPARENT FROM OBSERVATION OF THE 225° F. ISOTHERMS AT SUCCEEDING TIMES. NOTE THAT THE ISOTHERM MOVES TOWARD THE CENTER LINE AND FINALLY FOLDS IN TO FORM A ROUGHLY CIRCULAR AREA FROM WHICH THE TORUS IS DEVELOPED. 40

20 min. rrv h V r'^N »• K "\* 11 145 1127 n I II 175 i^ 2001 225' 250| 30 min. 207[ 195 J • 'v ' ' l\ ' ' 275 279°F 40 Mi A. '* V ' > ». 248|! 239 250 260 270 \ ' I > M ' 'l K\ !'|l| iV/;i f"w s /I 50 min. I 265 270' .s \ 262»» FIGURE 5. DISTRIBUTION OF ISOTHERMAL LINES IN THE HALF PLANE OF A CONTAINER BEING PROCESSED AT 279° F. AT 4 TIMES; 20, 30, 40, AND 50 MINUTES. IN THIS FIGURE THE 250° F. ISOTHERMAL LINE MOVES TOWARD THE CENTER AS TIME ADVANCES. BETWEEN 40 AND 50 MINUTES, HOWEVER, THE EMBRYONIC 250° TORUS PASSES OUT OF EXISTENCE DUE TO THE EFFECT OF INCREASED PROCESSING TEMPERATURE. AT 50 MINUTES, THE LOWEST ISOTHERM IS THAT FOR 261° F., LOCATED CONSIDERABLY AWAY FROM THE CENTER LINE OF THE CONTAINER. 41

lOmin. ISmin. ISO S---T^\X^ N j—--:^\! r' xv V\ I ' x'tMl*1 I/ \ \ I'll I If 11 I •III 175 L *-' . .„ 250 err 300L__^» ' 3I5°F 20min. | -N hl"IT\%i 181 -\ \\ \\ ivw)ii'i! 250'VN^ s/n 275n-^/// 25min. 222 225 250 275 k 300 L // / FIGURE 6. DISTRIBUTION OF ISOTHERMAL LINES IN THE HALF PLANE OF A CONTAINER BEING PROCESSED AT 315° F. AT 4 TIMES; 10, 15, 20, AND 25 MINUTES. AT THIS HIGH PROC- ESSING TEMPERATURE THE GREATLY INCREASED TEMPERATURE DIFFERENTIAL FROM THE OUTSIDE TO THE CENTER OF THE CONTAINER IS IMMEDIATELY APPARENT, BEING OF THE ORDER OF 100° F. AT 50 MINUTES AS COMPARED WITH APPROXIMATELY 15° F. FOR THE LOWER PROCESSING TEMPERATURES. ANOTHER EFFECT OF HIGH PROCESSING TEMPERATURE APPEARS IN THE FORM OF SOMEWHAT ENLARGED AREAS OF SLOWEST HEATING WHICH PERSIST THROUGHOUT THE TIMES SHOWN. 42

FIGURE 7. IDEALIZED CIRCULAR HALF-TORUS DIS- TRIBUTION OF LOWEST TEMPERATURES. FIGURE 8. IDEALIZED TRIANGULAR HALF-TORUS DIS- TRIBUTION OF LOWEST TEMPERATURES. In the event that some anisotropy exists in the medium a distribution of the form shown in Figure 3 might be expected in which a cardioid distribution would result with either one or both ends depressed. The existence of the cardioid is supported by experimental findings. The actual data from this experiment follow the pattern shown in Figures 4, 5, and 6. These figures illustrate the progression of isothermal lines in the half-plane of the container at 3 of the 6 processing temperatures used and for 4 times. Observation of each of these 3 figures indicates that for a great share of the time during the process the isothermal lines, if rotated through the 180° F., would tend to form roughly ellipsoidal shells. As time progresses at each tem- perature it should be noted that the isothermal lines tend to close at the center forming a roughly circular area located to the right of the can center and either on the horizontal central axis of the can or somewhat above or below it. These effects appear to be approximately the same at each of the representative pro- cessing temperatures used, suggesting that the effect of processing temperatures on this occurrence may be negligible. If the circular isothermal areas resulting from these processes were rotated through 180° F. in the can, the result would appear as shown in Figure 7, a solid geometric figure resembling half a doughnut. Geometrically, this is termed a torus or in this case a half torus and represents what might be termed an "iso- thermal volume of lowest temperature" at the time of observation. In actuality, it is difficult to explain this occurrence except on the basis of anisotropy in the medium being heated. If this effect does exist, it might be considered in terms of a distortion of the normal ellipsoidal distribution. Consider, for instance, the effect of the ends of the container on the distribution of temperature in the case where the distribution at the top may be concave upward and that at the bottom concave downward. In this case, the progression of portions of isothermals toward the center would result in the formation of a roughly triangular area somewhat off the center of the can which, were it to be rotated through 180° F. in the can, would form a torus resembling that in Figure 8. 43

While it is difficult to prove rigorously on the basis of existing data whether the torus described actually exists, the data from this experiment are concordant in that in almost every case this phenomenon was noted. If the existence of the torus may be taken as a fact, this phenomenon might be of considerable impor- tance in determining the sterility of a container of meat. In addition, the effect of such a temperature gradient upon the ultimate quality of the product, meas- ured in terms of tenderness, juiciness, flavor or otherwise, might be worth con- sideration. CHAIRMAN ROBINSON Thank you, Dr. Tischer. The next paper on the afternoon program will describe the effect of ingredient arrangement on the rate of heat transfer in canned meat products. We are very happy to have with us Dr. C. Olin Ball of Rutgers University, who will discuss this subject. Effect of Ingredient Arrangement on the Rate of Heat Transfer in Canned Meat Products C. OLIN BALL In conventional practice, a product requires severe heating during the sterilizing process because heat is transmitted through the product by conduction and therefore travels very slowly. However, when the formulation of the product is not completed by mixing the ingredients prior to filling into the can, one may take advantage of this fact to obtain an increased rate of heat penetration into the product during the sterilizing process. This is made possible by putting the ingredi- ents into the container under a special arrangement so that heat will flow through a part of the ingredients by convection. This technique had its first commercial application in 1950 on cream style corn in No. 10 cans—producing a sterile product of a quality as good as that pro- duced by conventional processes inadequate to destroy thermophilic spores. It is designed for use with products which constitute a mix- ture of discrete particles with a finely divided component of either the same or a different species of food. Procedures with cream style corn. As mentioned, the only product on which there is commercial experience is cream style corn. The procedure is as follows: the concentrated cream component, consisting of triturated whole corn kernels, is kept separated from the whole kernels and brine until after the sterilization is accomplished. Afterwards, the cream component is mixed with the brine and kernels either by shaking the sealed container or by stirring after the container is opened. In filling this product, the cream component, of course, is put into the con- tainer separately from the kernels and brine; then sterilization is carried out while the cream is kept stratified in a layer separate from the kernels and brine. The stratification of components is illustrated in a cross-section diagram of a can of cream style corn shown in Figure 1. About two-thirds of the can is filled with kernels of corn surrounded by water or brine and the layer above the kernels con- sists of finely ground corn kernels containing a small amount of water and possibly 44

FIGURE 1. STRATIFICATION or COMPONENT PARTS OF CREAM STYLE CORN IN THE CAN. Courtesy of Food Industries (now Food Engineering) some sugar and salt. During processing, heat flows into the product by convection and conduction along paths roughly indicated by the arrows in Figure 2. The mixture of thin liquid and kernels heats quite rapidly by convection while the layer of fine solid material heats slowly by conduction. Since the vertical dimen- sion of this layer is small, however, heat is transferred to the center of the layer \\ CONDUCTION INTO CREAM \ V I CONDUCTION INTO CREAM 11 \ FIGURE 2. ARROWS INDICATE PATHS OF HEAT FLOW BY CONVECTION AND CONDUC- TION INTO STRATIFIED PRODUCT. Courtesy of Food Industries (now Food Engineering) FIGURE 3. ARROWS INDICATE PATHS OF HEAT FLOW BY CONDUCTION INTO PRE- MIXED PRODUCT. Courtesy of Food Industries (now Food Engineering) 45

FIGURE 4 NUMERALS INDICATE PER CENT OF LETHAL HEAT REACHING DIFFERENT POINTS IN STRATIFIED AND PREMIXED PRODUCTS. Courtesy of Food Industries (now Food Engineering) in much less time than it takes to transfer heat to the center of a can containing a premixed product of sufficiently heavy consistency to necessitate all of the heating being done by conduction, as indicated by the arrows in Figure 3. The relationship between premixed cream style corn and the stratified pack in respect to sterilizing values is shown in Figure 4. The boxed numerals in the B diagrams indicate what percentage of the lethal heat that is necessary to sterilize the corn reaches each of several points in each can during a specified process. The first can, containing the stratified product, and the second can, con- taining the premixed product, are presumed to have received the same process—a process which is sufficient to apply to the surface of the container 765% of the amount of heat necessary to sterilize the surface layer of corn. During this pro- cess, the stratified corn is sterilized at its critical point, whereas, at the critical point in the premixed product, only 7% of the lethal heat necessary to sterilize the corn is effective. To sterilize the premixed corn at the critical point, the third diagram shows that surface layer would have to be subjected to 1235% of the amount of lethal heat necessary to sterilize the corn. Obviously, the quality of the premixed corn would be impaired much more during its sterilization than would the quality of the stratified corn during its sterilization. Equivalent pro- cesses at 250° F. for these 2 types of product in No. 2 cans are 74 minutes and 46 minutes, respectively. Relative rates of heat penetration in the 2 products in 4 different sizes of cans are shown by the curves in Figure 5. Procedures with meat (laboratory experiments only). What I shall say about meat products is based on laboratory experiments only. Four different for- mulated meat products were studied at Rutgers University in a project sponsored by the Quartermaster Food and Container Institute for the Armed Forces. These were ham and beans in molasses sauce, frankfurters and beans in tomato sauce, beef and vegetables in gravy, and meat balls and spaghetti. Temperature meas- urements in the can were made with thermocouples specially designed for this kind of work (4). In the calibration of the thermocouples an oil bath was used. With a thermocouple and a standardized mercury-glass thermometer placed close together in the oil, the bath was heated slowly and cooled slowly through the range of temperature of the calibration. Precisely timed readings were taken on both instruments throughout the periods of rise and fall of temperature and the time-temperature relationship of each was plotted on rectangular coordinate paper. For each temperature, the correction indicated by the rising curve was 46

190 170 190 A-2II-4OO(NO.ICAN) B - 307-306 (NO.2 VACUUM CAjv|) C- 303-4O6INa303 CANJ) D- 307-4O9fcTANDARDNO.2|cArvO PRE-MIXED E-2II-400(NO.ICANO F^3O7-306(NO.2 VACUUM CAN) G- 303-4O6NO.303 CAN) H- 0 10 20 30 90 MINUTES eo TO SO 9O FIGURE 5. RELATIVE RATES OF HEAT PENETRATION INTO STRATIFIED AND PRE- MIXED CREAM STYLE CORN IN CANS OF 4 SIZES. Courtesy of Food Industries (now Food Engineering) averaged with that indicated by the falling curve and the calibration curve for the thermocouple was made by plotting, in a smooth curve, these corrections against temperature. No significant correction was required in any case with the thermocouples used in these tests. Temperatures measured by the thermocouples were recorded on a Brown Electronik 12-point Strip Chart Recording Potentiometer having a chart speed of 20 inches per hour and a temperature range of from 0° to 350° F. Each product was studied, first, when formulated and packed according to Military specifications, second, when the method of packing the components in the container is altered—either without or with alteration in formulation from that of Military specifications. The initial objective was always to study the effect of rearrangement of component parts in the container without altering the nature and the proportions of the ingredients from those called for in the specifications. Then the investigation was extended to cover variations in the nature and, in one or two instances, the proportions of the ingredients for the purpose of seeking a modified formulation which will give best results with a modified arrangement of ingredients in the container. The rise of temperature'was measured at several points in each can; measure- ments were made at as many as 9 points in a can. This made it possible to con- struct isothermal and isochronal diagrams of a can to help determine the location of the critical point, and to compare the relative heat effects on the ingredients in different locations. Studies on specific products are reported as follows: Ham and beans in molasses sauce. This product was studied for rate of heat penetration with 5 different arrangements of components in the 404 x 404 can. These were: I. (a) on the bottom: raw ham slices, %-inch thick. (b) above the ham slices and extending into the upper portion of the can: blanched kidney beans. (c) water withheld from the sauce preparation (178.8 ml.) was poured over the beans. 47

TEMPERATURE — *T. FIGURE 6. RATE OF HEAT PENETRATION AT POINT OF SLOWEST HEATING IN EACH OF 3 CANS (1ST, 3RD, AND 4TH CANS OF TABLE 1) OF HAM AND BEANS IN MOLASSES SAUCE. (d) thick sauce (formulated without water) was spread evenly on top of the beans which were just covered with water. II. (a) on the bottom: one layer of ham slice, %-inch thick. (b) above the ham slice and extending past the middle of the can: blanched kidney beans mixed with a portion of the ham cut into pieces approxi- mately %-inch x %-inch x %-inch in size. (c) water withheld from the sauce preparation (178.8 ml.) was poured over the beans, not quite covering the beans. (d) thick sauce (formulated without added water) was spread evenly over the beans. (e) the remainder of the ham, a slice %-inch thick, was laid on top of the sauce. III. (a) on the bottom and filling the major part of the can: blanched kidney beans mixed uniformly with ham cut into pieces approximately %-inch x %-inch x %-inch in size. (b) water withheld from the sauce preparation (178.8 ml.) was poured over the mixture of ham and beans, not quite covering the mixture. (c) thick sauce (formulated without added water) was spread evenly over the ham and bean mixture. IV. (a) on the bottom and filling the major part of the can: blanched kidney beans mixed uniformly with ham cut into pieces varying from approxi- mately %-inch x 1-inch x 1-inch to approximately %-inch x 1 %-inch x 1 %-inch in size. (b) water withheld from the sauce preparation (178.8 ml.) was poured over the mixture of ham and beans, not quite covering the mixture. (c) thick sauce (formulated without added water) was spread evenly over the ham and bean mixture. V. Formulated and packed according to Military specifications. 48

Results Arrangement I gave a rather indefinite result and one which did not seem entirely logical; the critical point was indicated to be approximately in the center of the can but still the rate of heating was considerably higher than that of the product formulated and packed according to the Military specifications. Since the required process indicated by the test on one can was in the medium range, it was not considered worth while to take the time to clear up the inconsistency. Therefore, data are not available to show the effect of this arrangement of the product ingredients in the can. Results with arrangement II appeared to be reliable but here also the re- quired process was indicated to be one in the medium range. For the purpose of this paper, therefore, it will be passed by. The most significant results seem to be those obtained with arrangements III, IV, and V. These results are presented in Table 1. TABLE 1 HEAT PENETRATION AND PROCESS DATA—HAM AND BEANS IN MOLASSES SAUCE Arrangement > III IV V f» 34 24 27 80 f, 51.5 X'* 59 J 0.938 0.759 0.855 1.815 Process (min.) 50.5 28.8 31.6 95.6 Heating curves for the cans represented in the 2nd, 4th, and 5th columns of Table 1 are shown in Figure 6. The processes listed in Table 1 are based on the following specifications (1,2,3): z - 18° F. F — 5 min. RT = 250° F. IT = 150° F. CW = 60° F. These data indicate that the process at 250° F. required for sterilization of this product when filled into 404 x 404 cans in accordance with arrangement IV is less than one-third as long as that required when the filling is under arrange- ment V, i.e., in accordance with Military specifications. The process required under the filling procedure III is slightly more than half as long as that required when the filling is under arrangement V. Thus, the possibility of a considerably greater reduction in process through a particular arrangement of ingredients in the can is shown for ham and beans in molasses sauce than in corn. Frankfurters and beans in tomato sauce (307x306 cans). Heat penetration tests, made with 3 different arrangements of component parts in the 307 x 306 can, were as follows: I. (a) on the bottom and filling the major part of the can: frankfurter pieces (%-inch) and soaked and blanched beans. (These were put into the can and then shaken to mix thoroughly.) (b) water withheld from the sauce preparation (99.3 ml.) was poured over the mixture of frankfurters and beans, practically covering the mixture. 49

(c) thick sauce (formulated without water) was spread evenly over the frankfurter and bean mixture. II. (a) on the bottom and filing the lower part of the can: %-inch pieces of frankfurter. (b) soaked and blanched beans were filled on top of the frankfurter pieces. (c) water withheld from the sauce preparation (99.3 ml.) was poured over the beans, filling the interstices among the frankfurters and beans. (d) thick sauce (formulated without water) was spread evenly over the beans. III. Product was formulated and packed according to Military specifications. Results. In one respect, frankfurters and beans in tomato sauce is an ideal type of product to benefit from controlled arrangement of component parts in the can; the layer that heats by conduction (the sauce layer) is relatively thin dimensionally, and when this layer is in the top end of the can its center heats at practically the same rate as the critical point within the convection heating region containing the beans and frankfurter pieces. For example, in one of the 2 runs made with this arrangement of components, the slowest heating point was within the bean-frankfurter portion; in the other run it was in the sauce layer. Calcu- lated required processes in the 2 instances were 14.6 and 13.9 minutes, respec- tively—essentially the same. The indicated required process for arrangement II was slightly longer than those indicated for arrangement I. The process was 16.1 minutes and was based on the interior of the sauce layer. The longest process required within the con- vection region was 11.5 minutes. In 2 runs with arrangement III (Military specifications), the required pro- cesses were indicated to be 41.2 and 35.9 minutes, respectively. The above results, together with heat penetration data, are given in Table 2. TABLE 2 HEAT PENETRATION AND PROCESS DATA—FRANKFURTERS AND BEANS IN TOMATO SAUCE Arrangement > I II III fbl 8.2 5.6 7.7 34 22.5 *2 27.5 23.4 29.7 x'bh 4.5 5.4 30.4 j 0.241 0.512 0.874 0.492 1.076 Process (min. /250° F.) 14.6 13.9 16.1 41.2 35.9 The processes listed in Table 2 are based on the following specifications: z = 18° F. F = 5 min. RT = 250° F. IT = 70° F. CW = 70° F. These data indicate that the process at 250° F. required for sterilization of this product in 307 x 306 cans in accordance with arrangement I is slightly more than one-third as long as that required when the filling is under arrangement III, i.e., in accordance with Military specifications. The process required under II filling procedure is about two-fifths as long as that required when the filling is under arrangement III. Thus, the percentage of possible reduction in process obtainable through a particular arrangement of ingredients in the can is indicated to be about the same for frankfurters and beans in tomato sauce as in ham and beans in molasses sauce. 50

Heat penetration was studied in a product identical to the above except that only half of the specified amount of tomato pulp was put into the sauce. Cans of 307 x 306 size were used. Results obtained with this product are given in Table 3. TABLE 3 HEAT PENETRATION AND PROCESS DATA—FRANKFURTERS AND BEANS IN TOMATO SAUCE (50% OP SPECIFIED TOMATO PULP) fh, 10.7 10.5 6.4 17.8 17.8 f2 18.0 28.5 29.8 40.8 x'bh 88.33 5.4 16.8 21.5 j 0.346 0.396 0.340 0.922 0.950 Process (min.) 16.5 16.3 13.5 31.3 29.6 The processes listed in Table 3 are based on the following specifications: z = 18° F. F = 5 min. RT = 250° F. IT = 65° F. CW = 70° F. That there was some convection in the cans having filling arrangement III is shown by the fact that the rate of heating of the product containing only 50% of the specified amount of tomato pulp is higher than that for the product containing the full specified amount of pulp. (Compare Table 3 with Table 2.) As further evidence of convection in the former product, the critical point was found to be near the bottom of the can, which is a typical condition in cans that heat by convection. The process required for sterilization of this product, filled in accordance with arrangement I is slightly longer than that for filling arrange- ment II. This relationship is the reverse of that found for the product having the specified amount of tomato pulp in the sauce. Also, the locations of the critical points differ in the 2 formulations, as shown in Table 4. A partial ex- planation of this difference may rest in the difference in thickness of the 2 sauce layers. TABLE 4 LOCATIONS OF CRITICAL POINTS—FRANKFURTERS AND BEANS IN TOMATO SAUCE Amount Tomato Pulp Arrangement I Arrangement II 100% Specification 50% Specification Sauce Layer Sauce Layer Near Bottom Sauce Layer Sauce Layer Near Bottom For the product having 50% of the specified amount of tomato pulp, the re- quired process when filling arrangement either I or II is used is approximately one-half as long as that required when the product is formulated and packed according to Military specifications (arrangement III). The processes required for arrangements I and II are approximately the same as those required for the same arrangements in the product containing the specified amount of tomato pulp in the sauce. 51

Beef and vegetables in gravy. Heat penetration tests were made with 4 different arrangements of component parts in the 404 x 404 can, viz., I. (a) on the bottom, and filling about one-half of the can: meat pieces pre- pared by cutting raw trimmed beef into 1%-inch cubes and then cooking in one-half its weight of water until approximately a 35% shrink had been obtained. (b) on top of the meat: raw carrot slices %-inch thick. (c) on top of the carrots: %-inch to 1-inch cubes of partially cooked (blanched) potatoes. (d) beef broth equal in amount to that called for in the specifications plus that equal to 37% of the water specified for the gravy (222.25 ml. total) was poured over the potatoes, carrots, and meat. (e) gravy paste made by adding 34.02 ml. (63% of the specified amount) of water to the dry ingredients was spread evenly over the top of the potatoes. II. (a) on the bottom and filling most of the can: a mixture of cooked meat pieces, raw carrot slices, and cubes of blanched potatoes. (The meat pieces, carrot slices, and potato cubes were prepared in the same manner as for arrangement I.) (b) beef broth (the same amount as for arrangement I) was poured over the mixture of meat, carrot, and potato pieces. (c) gravy paste made by adding 63% of the specified amount of water to the dry ingredients was spread evenly over the top of the mixture of the pieces of meat and vegetables. III. Can was filled and sealed in same manner as for arrangement II; then the can was inverted for processing. IV. (a) pieces of meat, carrots, and potatoes, prepared as for arrangement I, were put into the can in the manner of arrangement I. (b) gravy prepared in accordance with Military specifications was poured hot over the potatoes, carrots, and meat. Results. As in frankfurters and beans in tomato sauce, the heavy sauce layer in beef and vegetables in gravy is quite thin dimensionally; thus, when this layer is in the top end of the can, the center point of the layer heats almost as rapidly as the critical point in the convection heating region containing the meat and vegetables. For example, in the product filled under arrangement I, the critical point was near the top of the can, whereas, with filling arrangement II, the critical point was near the bottom. With filling arrangement III, the critical point was near the bottom as is to be expected when the heavy sauce layer is in the bottom. A heavy sauce layer in the bottom of the can does not heat as rapidly as a similar layer in the top of the can. An interesting aspect of the results with arrangement I was that the point which heated most slowly was not on the longitudinal axis of the can, although it was in the heavy sauce layer. This indicated that the sauce layer was not of uniform thickness and that a thick part was away from the axis. Heat penetration data and calculated processes are shown in Table 5. TABLE 5 HEAT PENETRATION AND PROCESS DATA—BEEF AND VEGETABLES WITH GRAVY Arrangement > I II III IV fhl 31.7 29.3 38.0 87.7 77.0 79.5 f 167.5 x< 135.3 j ' 0.351 0.607 0.787 1.84 1.98 2.03 Process (min.) 23.6 29.2 39.1 103.9 95.5 98.6 52

The processes listed in Table 5 are based on the following specifications: z = 18° F. F = 5 min. RT = 250° F. IT = 70° F. CW = 70° F. It is seen from Table 5 that the required process for beef and vegetables with gravy is reduced by stratification of the components approximately as much as for the 2 products previously discussed. Spaghetti and meat balls. The last of the formulated meat products to be studied, spaghetti and meat balls, gave variable results. In filling arrangement I, the bottom layer was meat balls prepared according to Military specifications, followed by a layer of blanched spaghetti, over which was poured the water with- held from the sauce. In the top was the sauce paste layer. The product with this arrangement was too bulky to permit proper sealing of the can. In filling arrangement II, the order of the 2 layers (meat balls and spaghetti) was reversed; otherwise, was like arrangement I. This arrangement produced no increase in the rate of heating over that of the product formulated and packed under Military specifications. In filling arrangement III, the meat balls and spaghetti were mixed and formed a single layer over which was spread the sauce paste. This arrangement showed a 31% reduction in length of process, but the product could not be recon- stituted except by the addition of water after the product was removed from the can. The water put into the can with the spaghetti and meat balls was all absorbed by the spaghetti. It should be noted, however, that the process used in this test was considerably longer "than that required for sterilization of the product. Discussion of results. Samples of all of the products discussed ex- cept spaghetti and meat balls, packed with the modified arrangements of component parts were pronounced by taste test panels to be superior in flavor and appearance to the similar products packed in accordance with Military specifications. For the products containing beans, how- ever, the over-all preference was tempered by opinions that the beans showed unsatisfactory absorption of sauce flavor and were not suffici- ently cooked. A complete remedy for this defect may be found only in a mod- ified pretreatment of the beans, in which a precook of increased sever- ity is used under conditions which permit the beans to absorb desired flavors. However, a partial remedy can no doubt be obtained by put- ting a small quantity of the flavoring ingredients of the sauce into the water which covers the beans during the processing. This will cause some reduction in the rate of convection heating which takes place, but it need not increase the process required for sterilization. In fact, it might reduce the required process slightly because the dimensional thickness of the conduction heating layer would be reduced by the transfer of solids from that layer to the liquid in the convection heat- ing region while still not causing a sufficient reduction in the rate of convection heating to reduce the rate of acquisition of lethal heat at the critical point in this region below that at the critical point in 53

the conduction heating layer. In other words, this change in pro- cedure causes the critical point in the conduction heating layer to ac- quire lethal heat more rapidly and the critical point in the convec- tion heating region to acquire lethal heat more slowly, causing the 2 rates to approach each other in value. When this packing and processing procedure was introduced a few years ago, justifiable skepticism was expressed as to whether or not the stratified layers would remain stratified during the heat ster- ilizing process. Experience not only with corn but also with the meat products discussed herein has shown that this skepticism was not jus- tified ; on the other hand, the only problem involved here points in the opposite direction—the difficulty of reconstituting the product. Recon- stitution by shaking the can is always facilitated by higher tempera- tures in the product; when the product is cold, that is, at room tem- perature, violent shaking is required to destroy the stratification and thoroughly mix the ingredients. The greater the head space in the can, of course, the more easily the product is mixed by shaking. Under regulations promulgated by food control authorities, there is a limit to the maximum amount of head space permitted; also, in most packing plants, it is not feasible to shake the cans until after they have been completely cooled. It is doubtful whether some prod- ucts can be put into homogeneous state by shaking the cooled cans. Ham and beans in molasses sauce and beef and vegetables in gravy are in this category because the heat of processing causes the heavy sauce layer to assume a rubbery texture after cooling. This texture is quickly 'destroyed by heat, however, so that by heating moderately in a kettle with stirring, the formation of a homogeneous mixture is easily accomplished; better still, if the product is being prepared for eating, heating it in a kettle by convection before stirring speeds the heating process just as it does in the can during sterilization. After it reaches boiling temperature, it may be quickly mixed by stirring. Whenever it is feasible to shake the sealed container while the con- tents are warm, a preferred temperature for the product is generally within the range of from 150° to 200° F. Various factors, such as the order of filling the various layers of ingredients, the size of pieces of the fleshy components, and the amount of thin liquid used were shown to affect the rate of heat penetration to the critical points in the cans. For example, ham and beans in molasses sauce heated more rapidly when pieces of ham measuring %-inch x 1-inch x 1-inch were mixed with the beans than when smaller pieces of ham were mixed with the beans. The numerical comparisons presented in Tables 1 to 5, however, should merely be regarded as approximate, since a comparatively few cans of each product were included in the experiments. More extensive experiments would be required to establish accurately the ranges of the heat penetration 64

and process factors. The values given, however, are, no doubt, typi- cal of the true results, since the work was done with meticulous care. In the experiments with the 4 meat products, closing tempera- tures varied considerably in the stratified products. The component parts of ham and beans in molasses sauce were filled at room tem- perature, then the open cans were exhausted in steam until the aver- age temperature of the contents was from 160° to 180° F. The cans were then sealed. For the frankfurters and beans in tomato sauce, the beans were blanched at 180° F. for 20 minutes just before filling but the other ingredients were filled at room temperature. The cans were then sealed under 23-inch - 25-inch vacuum. The ingredients of beef and vegetables in gravy, except the water, were heated to at least 150° F. just before filling. The cans were sealed at atmospheric pressure. Meat balls and spaghetti ingredients were filled at room temperature and the cans sealed under atmospheric pressure. It is thought that the temperature conditions at the time of sealing had no material effect upon the results of the experiments. In addition to check runs on the tests already made, a study of additional variables might yield information more interesting than that already obtained. Among the additional variables would be the mixing of a part of the sauce solids into the liquid of the convection region and mild agitation of the can during processing. Depending upon the nature of the stratification, slight agitation, such as very slow rotation, of the can may further increase the rate of heating of the stratified product and at the same time bring about a partial recon- stitution of the product during processing. Summary Heat penetration tests were made of 4 formulated meat products, used as ration items by the Armed Forces, in which the component parts were stratified in the can during processing so that the portion in the center of the can would be heated by convection and the portion in one or both ends of the can would be heated by conduction. Processes calculated from the heat penetration results showed that sterilization can be accomplished in the stratified products in much less time than in the same products formulated and packed in accordance with Military specifications. Reduction in processing time at 250° F. amounted to from 47 r/r to 70% for ham and beans in mo- lasses sauce, from 44% to 65 % in frankfurters and beans in tomato sauce, from 59% to 77% in beef and vegetables in gravy, and approx- imately 30% in spaghetti and meat balls. Flavor and appearance of the products sterilized in stratified state were improved over flavor and appearance of the same products packed according to Military specifications. 55

Acknowledgement The results presented herein of results of tests on meat products were taken from reports prepared by Messrs. Richard C. Kennedy and Abner Salant, who carried out the experimental work. The author's indebtedness to Messrs. Kennedy and Salant is hereby acknowledged with sincere thanks. Literature Cited 1. Ball, C. 0. Mathematical solution of problems on thermal process- ing of canned food. Univ. of Calif. Publications in Pub. Health, 1, 2, 15-245 (1928). 2. Ball, C. O. Supplement to mathematical solutions of problems on thermal processing of canned food. 1-25 (1936). 3. Ball, C. O. Thermal process time for canned food. Bull. Natl. Res. Council, 7, Part 1, 37, 1-76 (1923). 4. Eklund, O. F. Apparatus for the measurement of heat penetration in canned foods. Food Technol, 3, 231-233 (1949). CHAIRMAN ROBINSON Thank you very much, Dr. Ball. The final paper on this afternoon's program, prior to our round- table discussion, will be presented by Mr. James M. Blair, QMFCI; co-author is Dr. K. T. Swartz. Preliminary Observations on the Effect of Can Movement During Thermal Processing JAMES M. BLAIR It has been obvious for many years that the conventional methods of stabilizing canned meats by heating with steam have been very deleterious to the quality of the product. Greenwood et al. (4) clearly demonstrated that in canned pork luncheon meat good vitamin reten- tion is dependent upon rapid, uniform heating of the entire contents of the can. Uniform heating reduces the temperature differential be- tween the inner and outer portions of the material. Various devices and methods used to reduce the heating time required to sterilize various canned vegetables and fluid goods have been considered for some time and in some instances are used indus- trially with considerable success. By means of these procedures and mechanical devices, there have been produced rather fluid, free-flow- ing foods possessing a texture, flavor, and appearance superior to those qualities in the same material when heated conventionally. 56

FIGURE 1. THE RETORT USED IN THESE EXPERIMENTS PERMITTED ROTATIONAL AGITATION OF CANS IN VARIOUS POSITIONS AT SELECTED ROTATING SPEEDS. The procedures usually employed in increasing the rate of heat pene- tration in free-flowing canned food products have essentially involved some type of agitation of the food during the sterilizing heating period. Clifcorn et al. (1) and Conley et al. (2) have presented some of the characteristics of agitating retort operation and have firmly established fundamentals essential to the successful application of this process. The major portion of the work by these authors deals, how- ever, with free-flowing materials such as water, tomato juice, and brine-packed corn and peas. In the case of canned meats, relatively few attempts have been made to reduce required heat-sterilization periods by means of can agitation. Very likely, this lack of investigation has been due to the common and perhaps justified belief that the more or less solid or viscous canned meat products transmit heat slowly and, because of FIGURE 2. REAR OF RETORT WITH CON- STANT TEMPERATURE CON- TROLLER AND AUTOMATI- CALLY RECORDING POTEN- TIOMETER IN THE BACKGROUND. 57

FIGURE 3. AGITATING DRIVE MECHA- NISM AND SLIP-RING, FRIC- TION TYPE COMMUTATOR. their physical attributes, resist any form of agitation intended to in- crease the rate of heat penetration into the mass as a whole. The purpose of this investigation has been to consider the prin- ciples of agitation of canned meats and to determine the extent to which they can be utilized to improve canned meats. The data ob- tained to date are preliminary in nature, but with the accumulation of additional experience, it is anticipated that it will be possible to deter- mine the extent to which agitating processing will improve the gen- eral quality of canned meats. It is also anticipated that it will be possible to formulate canned meat items that will be conducive to a more rapid heat transfer during an agitation process. FIGURE 4. INTERIOR OF RETORT WITH CANS POSITIONED FOR SI- MULTANEOUS STILL AND AGITATING COOKS. 58

Experimental Equipment. The equipment used in these studies has been designed to permit considerable flexibility in experimental methods. The retort permits rotational agitation of cans in various positions ("on-side" or "end-over-end") at rotating speeds ranging from 4 to 104 r.p.m. The rotational radius for each can used in these experiments was 14 inches (range of 7 to 14 inches permitted) from the center of the rotating axle to the can center. Thermocouple leads (copper, constantan) pass through the hollow axle of the agitating device and at the rear of the retort make contact with potentiometer leads by means of a slip-ring friction-type commutator. A shelf in the front portion of the retort is designed to hold cans that are to be still-cooked simultaneously with the agitated cans. Thermocouple leads for these still-cook cans pass through a port in the top of the retort. The capacity of the retort permits simultaneous processing of 12 agitated cans (size 300x200 to 603x700, 6 fitted with thermocouples) and 6 thermo- couple-fitted still-cook cans. Temperature is limited by a steam supply with a pressure of 35 p.s.i., but in the near future a steam generator capable of supplying pressures up to 100 p.s.i. will be available. Suitable water and compressed air inlets permit pressure cooling of cans. The operation of the retort is manual except for the use of a constant temperature controller. Details of the mechanical apparatus are pictured in Figures 1, 2, 3, 4. The thermocouples used are of the type described by Ecklund (3), and temperature and time are automatically recorded by a 12-point recording potentiometer. Methods. Bentonite dispersions were prepared essentially as described by Jackson and Olson (5). Powdered laboratory-grade bentonite was added, with TABLE 1 SUMMARY OF TEST PROCEDURES USED TO DETERMINE THE EFFECT OF END-OVER-END AGITATION OF THE RATE OF HEAT PENETRATION IN VARIOUS MATERIALS Purpose of Experiment Test Material Test Conditions To determine optimum r.p.m. for agitated heating of test materials 5% Bentonite ' (3 thermocouples per can) "Still-cooked" cans — 0 r.p.m. Agitated cans — 36 & 81 r.p.m. (12 r.p.m. during cooling) To determine rate of heat penetration in different materials during agitated heating 1, 5, and 10% Bentonite* "Still-cooked" cans — 0 r.p.m. Agitated cans — 36 r.p.m. (12 r.p.m. during cooling) Luncheon Meat c "Still-cooked" cans — 0 r.p.m. Agitated cans — 36 r.p.m. (12 r.p.m. during cooling) Frankfurters « "Still-cooked" cans — 0 r.p.m. Agitated cans — 28 r.p.m. (12 r.p.m. during cooling) " Data are presented in Figure 5. b Data are presented in Figure 6. « Data are presented in Figure 7. * Data are presented in Figure 8. 59

MO 9% B»ntonile Can SiM 4OI • 411 3 ttiarmocoLiplts tod* con 1/2" HMdlpoct RT.. 260 «F 60 'i FIGURE 5 EFFECT OF RATE OF AGITATION ON RATE OF HEAT PENETRATION IN 5% BENTONITE DISPERSIONS constant mechanical mixing, to a specific amount of water. After thorough mechanical mixing to eliminate all noticeable lumps, the dispersion was allowed to stand for 4 hours before filling into cans. At the time of filling, careful con- sideration was made of gross head space, net weight, position of thermocouple, and closing vacuum. The cans were then given a preliminary heating to the retort test temperature. The 2 food products tested, frankfurters and pork luncheon meat, were prepared according to Military specifications covering the manu- facture of these items. Again, net weight, gross head space, vacuum, and thermo- couple position were carefully noted. The sealed test cans were placed in the agitating device of the retort in such a manner as to provide end-over-end type agitation. Identical test cans were placed in a vertical position on the shelf in the forepart of the retort and served as controls in determining the effect of agitation on the rate of heat penetration into the cans. The retort was operated in such a manner as to provide the most rapid come-up time possible with the relatively low steam pressure available. The time required for the retort to attain 250° F. was 10 minutes. The agitating device was operated at a constant speed throughout the process,-- except during cooling, when the rotational speed was decreased to 12 r.p.m. to prevent possible damage to equipment by creating excessive turbulence in the cooling water. Time and temperature measurements were made throughout the entire heating and cooling periods. The experimental test procedure is summarized in Table 1. Results Early in the experimental phase of this investigation, it was apparent that many conditions could very likely affect the heating characteristics of any sub- stance being agitated during heating. The 2 factors considered to be most impor- ' Differing, of course, with each process in accordance with the test requirements. 60

Coif 300 < 306 I • Z50'F SMI-Cooked COM: WtiCOl POSil Agitated cons 36 urn. End-OMf 90 40 TIME-MINUTES FIGURE 6 RATE OF HEAT PENETRATION IN BENTONITE DISPERSIONS DURING "AGITATED" AND "STILL" COOKS tant in affecting the rate of heat penetration into cans being subjected to end-over- end agitation were the amount of head space and speed of rotation. The amount of net head space used was arbitrarily determined at %-inch for 401 x 411 size cans, and ^4-inch for 300x308 size cans. This head space was considered to be realistic with regard to a reasonable fill for the container and yet sufficient to permit a satisfactory amount of movement of the contents during agitation. The approximate speed of rotation of the agitating device, which would permit the most rapid rate of heat penetration into a 5% bentonite dispersion, was determined experimentally. To do this, 401 x411 size cans were fitted with 3 thermocouples each. The thermocouple hot junctions were located on the long axis of the cans with one thermocouple 13/16-inch from each can end and the 3rd located at the can center. Figure 5 indicates the range of temperature differences recorded by the 3 thermocouples during still and agitated (36 and 81 r.p.m.) cooks. The graph illustrates the wide range of temperature differentials recorded by the 3 thermocouples in the still-cooked cans and in the agitated cans rotated 81 r.p.m. In contrast, the cans rotated 36 r.p.m. heated at a greater rate than did both the still-cook and 81 r.p.m. agitated cans, and the 3 thermocouples recorded essentially the same temperatures during the heating period. On the basis of this and other similar determinations, the agitation speed considered to be optimum in resulting in the greatest rate of heat penetration in products similar in density to a 5% bentonite dispersion is in the range of 36 r.p.m. This method of deter- 61

mining optimum r.p.m. is considered to be a practical means of determining, during actual heating, the optimum conditions of agitation for any test material. The basic assumption of this procedure is, of course, that during heating the temperature will be uniform throughout the mass of a well-agitated material. The study of the effect of agitation on the rate of heat penetration in various materials has resolved itself into a consideration of 4 different heating conditions. Strict convection heating. This terminology is applied to the heating condi- tion where the method of heat transfer throughout the can is principally by con- vection, both during agitated and still-cooks. Figure 6 indicates that, with the relatively fluid and free-flowing 1% bentonite dispersion, the rate of heat transfer to the center of the still-cooked can is nearly as rapid as in the agitated can. Although this does not imply that the temperature distribution in the still-cooked is as uniform as that in the agitated can, it does suggest that naturally-induced convection currents are quite strong, and that agitation of an item of such con- sistency offers no advantages over conventional still cooking in increasing the rate of heat penetration to the center of the can. Induced convection heating. Induced convection heating is a term applied to the heating characteristics of a substance with such a viscosity as to cause the product to exhibit conduction-type heating characteristics when still cooked and yet be of thin enough consistency to permit flowing when agitated and thus dem- Con Sue 401 « 411 Retort Temp « 240 "F Still-Cooked Cons, vefticol Position Agitoted Conv End-Over-Cnd 36rpm 40 50 60 TO 10 TIME-MINUTES FIGURE 7 RATE OF HEAT PENETRATION IN LUNCHEON MEAT DURING "AGITATED" AND "STILL" COOKS 62

onstrate convection-type heating characteristics. Figure 6 illustrates this by comparison of the rates of heat penetration to the center of the can of 5% bentonite when both agitated and still cooked. The difference in the slopes of the 2 curves is considerable, with the still-cooked cans exhibiting convection-type heating characteristics that very nearly resemble those of the 1% bentonite (both agitated and still cooked). Strict conduction heating. This term has been applied to the heating charac- teristics of products that exhibit no appreciable difference in rate of heating when either agitated or still cooked. The heating characteristics of a 10% bentonite dispersion (Figure 6) illustrate this classification. Here, both the agitated and still-cooked cans heated at essentially the same rate. Thus, the physical nature of a 10% bentonite dispersion is representative of products for which agitation will offer little advantage in increasing the rate of heat penetration. Luncheon meat, as indicated by can No. 1 in Figure 7 apparently represents strict conduction heating. Combination conduction-convection heating. The heating characteristics of most food items probably fall into this classification. Most canned foods consist of rather dense particles surrounded by a fluid, free-flowing medium. This fluid medium can be either an added specific ingredient or consist of juices and melted fat rendered from the product during the early stages of the process. The success IM ReioM Temperoture =240 "f Still CaoM cans- Vertical Agitated cons- End-ovw-End 28rpn FKAHKFURTfHS -L L 10 15 TIME-MINUTES FIGURE 8 RATE OF HEAT PENETRATION IN FRANKFURTERS DURING "AGITATED" AND "STILL" COOKS 63

of an agitated cook in increasing the rate of heat penetration in these items would depend upon a rapid transfer of heat to the fluid portion by induction of con- vectional currents that otherwise would not exist. The hot fluid would then trans- mit heat to the solid portions which would in turn heat by conduction. Thus, the heating time required by the slowest heating portion of the contents of the can would be less than if the entire material heated by conduction only. Luncheon meat, as illustrated by can No. 2 in Figure 7, represents the type of heating whereby hot juices, rendered from the product, can force their way through the meat mass and cause a convection-type transfer of heat to solid particles. This channeling of the hot juices is apparently enhanced by agitation of the can during cooking, but it is likely that this effect can also take place in still-cooked material. The development of fissures in bulk-pack meat items such as luncheon meat makes it difficult to determine if the temperature measured is representative of the slowest heating portion of the mass. These fissures also render the yield and appearance of the product undesirable. It remains to be seen whether or not the development of fissures and poor yield will be a typical problem peculiar to the agitation cooking of products of this type. The heating characteristics of frankfurters illustrate this combination con- duction-convection method of heat transfer with much less variability than does luncheon meat. One pound and 6 ounces of frankfurters, in 401 x 411 size cans, topped to within %-inch of the top of the can with water, heated at the same rate when both agitated and still cooked. This is illustrated in Figure 8. Here, temperature was determined at the center of the frankfurter. It is likely that the water portion of the contents of the cans exhibits the characteristics of strict convection-heating items described previously, whereas, the frankfurters alone heat as strict conduction-heating items. This is suggested by the similar rates of heat penetration into both the still-cooked and agitated cans and probably results from the orderly arrangement of frankfurters in the can, which permits almost uninhibited flow of juices. A 3rd type of product which is yet to be investigated should be included in this classification. This material consists of irregularly-shaped solid conduction- heating particles arranged at random in a fluid, convection-heating medium. These solid particles would inhibit the flow of natural convection currents induced during still-cooked heating, and yet, during an agitated cook, could aid in the generation of rather vigorous convection currents. Discussion These preliminary observations on the effect of can movement, or agitation, during heat processing have been primarily intended to indi- cate the procedures to be used in the experimental agitated processing of canned meat products. Bentonite dispersions of various concen- trations have proved to be useful in establishing some of the funda- mental characteristics of agitating-retort procedures. However, the use of these materials will be more limited when consideration is to be given to materials possessing more complex physical characteristics. One observation pertaining to agitated heat-penetration charac- teristics does stand out, however. Materials similar in consistency to 1% bentonite dispersion heat rapidly when still-cooked by means of natural convection currents that are almost as strong as those pro- duced by agitation. Thus, agitation would appear to be of no benefit in appreciably shortening the required process time for these mate- rials. It is possible, however, that delicate items subject to surface 64

burning are benefited by agitation, but very likely this does not apply to canned meats since the fluid portions of these products that re- semble a \% bentonite dispersion are primarily water or brine. For products in this category, the nature and arrangement in the can of the solid particles is critical. The type of heat transfer represented by passage of currents of vapor throughout a vacuum-pack can during heat processing has not been considered here. This method of heat transfer can be con- sidered as a convection type, but it is believed not to be applicable to most meats. Canned meat products which possess, either wholly or in some component part, a physical consistency comparable to that of a 5% concentration of bentonite in water are very likely those products in which it will be possible to effect an appreciably greater rate of heat penetration by means of agitation during retorting. With products of this nature, much attention should be allotted to the nature of the fluid portion and the form and distribution of the solid portion. Canned meat products essentially solid and uniform throughout deserve specific consideration because of the particularly excessive amounts of heat required for their sterilization during conventional retorting. As indicated by the unaffected rates of heat penetration obtained in 10% bentonite suspensions during agitated retorting, it appears likely that agitation will be of no value in decreasing required heating time in canned meats possessing similar consistency. It is yet to be determined if solid-pack canned meats do possess the heating characteristics of a 10 % bentonite dispersion. Agitation heat-pene- tration studies on some of these items are complicated by the chan- neling of juices and melted fat which probably results in an irregular distribution of temperature throughout the mass. Possibly other fac- tors also affect the rate of heat penetration into solid particles,-and all should be considered before agitated retorting is discounted as a means of improving the quality of such items. Summary It has been demonstrated that agitation of the can will not ap- preciably increase the rate of heat penetration in a \r/< bentonite dispersion. Materials of similar consistency are therefore classed as strict convection-heating types since the application of heat alone will establish strong convection currents. The rate of heat penetration in a 5% dispersion of bentonite can be greatly increased by means of agitation. Materials of this con- sistency are identified by the term induced convection heating in that strong convection currents cannot be formed by the application of heat but can be established by agitation. Thus, when agitated, the rate of heat penetration in this material resembles that of a strict convection-heating material. 65

A 10% suspension of bentonite in water will demonstrate the same rate of heat penetration when agitated as when still retorted. This rate of heat penetration resembles that of the still-cooked 5% bentonite dispersions. Materials similar in consistency to a 10 % ben- tonite dispersion are therefore classified as strict conduction-heating types. The heating characteristics of most canned meat items involve a combination of methods of heat transfer described above and are classified as combination conduction-convection heating types. The characteristics of each particular item in this category determine whether or not agitation can be effective in increasing the rate of heat penetration. A method of using 3 thermocouples in one can has been found effective in determining the optimum conditions of agitation. Literature Cited 1. Clifcorn, L. E., Peterson, G. T. Boyd, J. M., and O'Neil, J. H. A new principle for agitating in processing of canned foods. Food Technol, 4, 450 (1950). 2. Conley, W., Kaap, L., and Schuhmann, L. The application of "end- over-end" agitation to the heating and cooling of canned food products. Food Technol, 5, 457 (1951). 3. Ecklund, 0. F. Apparatus for the measurement of the rate of heat penetration in canned foods. Food Technol., 3, 231 (1949). 4. Greenwood, D. A., Kraybill, H. R., Feaster, J. F., and Jackson, J. M. Vitamin retention in processed meat. Effect of thermal processing. Ind. Eng. Chem., 36, 922 (1944). 5. Jackson, J. M., and Olson, F. C. W. Thermal processing of canned foods in tin containers. IV. Studies of the mechanisms of heat transfer within the container. Food Research, 5, 409 (1940). Discussion CHAIRMAN ROBINSON Thank you very much, Mr. Blair. To start out the panel this afternoon, I am going to call on Dr. Back, chairman of the National Research Council Committee on Foods, which is advisory to the Quartermaster Food and Container Institute. The committee represented here today is one of the sub- committees of Dr. Dack's Committee on Foods. Dr. Dack. GAIL M. DACK Dr. Ayres, when you reported those counts in the raw meat prod- ucts, why were they so low? I was wondering whether consideration had been given to some of the work done in the 19th century—for example, to that of Louis Pasteur or to that of Claude Bernard. The latter noticed that freshly drawn blood did not putrefy or spoil for 66

some period of time. There is a considerable normal bactericidal prop- erty present in blood. Has any consideration been given to that fact in relation to fresh meats? Is there any normal bactericidal mech- anism and has it been tested, say, against fecal contamination? Cer- tainly, in dressing any carcass, we would expect a more liberal fecal spread of organisms than is sometimes indicated in some of the counts that have been given. AYRES There are, of course, many reports concerning the bactericidal action of blood. However, the meat that we studied wasn't as fresh as even 2 or 3 hours, and so the counts reported do not reflect the liv- ing animal condition at all. The counts of putrefactive anaerobes were made low in order to eliminate anaerobic organisms—the only way we thought it possible was to heat the material to 80°C. for 20 min- utes. That eliminated the non-spore-forming organisms, supposedly, and so the putrefactive anaerobic spores would have to go through that preliminary heating process. It does not necessarily mean that we have all of the putrefactive anaerobic spores when we report our counts on those particular organisms. We have just those that are able initially to go through 80°C. for 20 minutes; in many instances that heat was worse than the process that was given to them later on. In regard to some of the processing times Dr. Tischer has shown, I would imagine the actual value was of such order that it would have been less than the heat necessary even to separate the spore formers, from the non-spore-former organisms. TISCHER May I add a comment to that? Going on with Dr. Ayres' discus- sion, one other important point in answer to Dr. Dack's question is that in the rather wide range of processes, the fact should be kept in mind that in these lower times some of the large differences in steri- lizing values probably occurred in the higher temperatures in the shorter time because, as is rather obvious, the temperature gradient in the can would be magnified considerably. Under these conditions one might consider all the concepts of bacteriology together. The gradient in the can would again be an important aspect in deciding exactly what the end result. Results depend also upon the location in the container of the points being considered and upon the existence of the gradient. I don't see how you can make an answer which would bear any weight unless you specify some restrictions on the location within the container. AYRES I might say, too, the counts here were so low that we had to go to the most probable number technique; in doing that in some of the trials we had to use the entire contents of the can even to get a count. 67

G. R. MANDELS (Philadelphia QM Depot) What is the bacterial content of this type of meat? If you sterilize a piece of meat before it has a chance to stand around, what would the bacterial count of that be—anything like that in the normal tissue? AYRES I would like to know that, too. I would say that the count can range over wide gradients. We have found in some samples less than one organism. That's total count. I am talking about an entirely different thing when I am talking about putrefactive anaerobes counting 200 or 300 g. and not getting a count. But usually the count ranged between 10,000 and a million on the surface. Below the surface there aren't many organisms, or we haven't found many organisms; with the fresh meat, we found very, very few organisms, even slightly below the surface. Most of the organisms are those that seem to come in contact with the meat during the slaughtering op- erations, from hands of workmen, and from other sources such as that. There are some that could get in by way of the intestinal tract and then through the intestinal walls. There are some that could get in by still other pathways, such as the air. MANDELS Is it entirely out of the question to surface-sterilize a piece of meat and then place it in a sterile can—that is, do this more or less aseptically? They handle drugs that way. Is it feasible to do it in the packing industry? AYRES It is not at all out of the question. I think a lot of people would like to know how to do it successfully in the packing plants. TRESSLER I would like to ask Mr. Blair or Dr. Swartz whether or not that 10% bentonite solution was in effect a jelly or whether it was a vis- cous liquid. It would seem to me if it were a viscous liquid, the answer to their problem is either more rapid agitation or more violent agita- tion. If it is a jelly so that there can be substantially no convection currents, then I assume that all you can expect is to heat it by con- duction rather than convection. BLAIR Actually the 10 % bentonite is of very thick jelly-like consistency. In fact, if you were to thump the side of a can with your finger, it would have a sort of ring to it. It is really a solid .and, I think, is very characteristic of a strict conduction-heating substance. I have never thoroughly tried all types of agitation or various speeds of agitation with that material, but it would seem that pos- 68

sibly the material does approach a condition of a truly conduction- heating chunk of meat. I can visualize a chunk of meat with some passage of juices through the material, and I rather doubt, although I don't know, that such would be the case with that 10% bentonite. A. STUART HUNTER (OQMG) Dr. Ball, I would like to ask 2 questions. Did you check the ac- ceptability of the products out of the 2 cans—the one heated 4 times as long as the first one to get sterilization? Second, assuming you were to adopt the rapid method, wouldn't you encounter the necessity of very careful product control? If something happened to break up stratification in the can, the treatment wouldn't sterilize the unit, and you would be in for trouble. BALL We did check, by means of a taste panel, the organoleptic quality. It was put through regular panel procedures, and they said there was quite a distinct difference. Dr. Swartz said that they made a couple of difference tests at the Institute. On the first one they did not seem to find any difference. On the second, if I remember rightly, there was a difference. As to the control that is necessary, it would appear that there might be some rather difficult problems, but it has not been found true in the case of corn. It is comparatively simple to get uniform conditions. Mechanical fillers fill the different components. The ac- curacy of those fillers is well known. The processes are established on such a basis that any variation will be taken care of. It is not very difficult because you know the variations pretty well. J. T. R. NICKERSON (M. I. T.) Dr. Ayres, the Australians say a good deal of the contamination on the surface of the carcass comes from the hide. They have suggested that the cattle be given a chlorine dip prior to slaughter. HALVORSON I would like to comment on that point from observations I made a number of years ago. Probably many of you remember that several years ago the American Meat Institute reported they could find viable spores in the tissue of living animals. That may well be the case. But any way, it intrigued me, and I thought I would try to prove that that might have been due to faulty technique. I took some kidneys and sterilized the outer cavity. The capsule was left on. I dipped some of them into a bacterial culture; one was Staphylococcus aureus. I im- mediately took the kidneys out and dipped them into a solution of chlorine; others into bichloride of mercury. Then I took them out with sterile instruments and dipped them into a solution of counteracting 69

germicide. I had hypochloride, I had thiosulfate, and with bichloride of mercury, a sulfite solution. From there the kidneys were taken on to a sterile cloth, opened with a sterile knife, and with another sterile knife I cut out a piece of center. In every instance I found the contaminating organism on the dipped kidney and inside of the kidney. I concluded it would be dif- ficult to sterilize the outside surface of a piece of meat and avoid contamination when you went in with instruments later on. It would be extremely difficult to sterilize the outside of a hog by dipping in solution. AYRES Knowing the difficulty of getting a chlorine residual in a swim- ming pool, I can imagine what it would be on the surface of a living animal in contact with a lot of organic material. GEORGE BRISSEY (Swift & Company) I would like to ask Dr. Gross if he has any theories or facts concerning the apparent auto-sterilization of the long-incubated samples of lunch meat. GROSS I wish I had, but I haven't a single thought on the subject. We never expected any such thing in view of the statements in the liter- ature that some of these spores had been known to survive 20 decades. Those conditions of survival were unusually adverse to any possible germination. We have done a little thinking ourselves, but I even hesitate to voice it here except to say that we thought there might be the possibility, an approach, let's say, to favorable conditions for the growth of some of these. Under these favorable conditions the or- ganisms attempt to germinate, and when they do, they remain in that stage; neither go forward nor backward, and eventually die there. I wonder if Dr. Halvorson has any thoughts on the subject. HALVORSON The experiments we did on spores in rancid fats—reported by Jackson and Foster—show that the fatty acid inhibits the germination of spores. We thought we had confirmed that to show it was due to rancid fats. Later work which we haven't published yet threw some doubt upon this. We determined germination by plating the spore suspension on suitable media where they could grow, and if the or- ganism did not form a colony, we assumed it didn't germinate. We have now repeated that work and observed germination through the microscope. We find the rancid fatty acids did not prevent germination, but killed the newly formed vegetative cell; therefore, it can't form colonies. 70

It is our opinion that the newly formed vegetative cells are more sensitive than the regularly growing cell. You sometimes report in- hibitors as inhibiting germination when, in fact, they are inhibitors that killed the newly-formed cell. Maybe some of your curing in- gredients would not necessarily prevent germination of the spore, but they might kill off the newly formed cells. GROSS Mr. Chairman, to add one statement to what I said this morning —one tube in the several thousands did germinate on incubation; that was at the critical point where they either die out or are com- pletely inhibited from further growth, whatever you want to call it. When we examined all the rest of the tubes from that lot which were still under incubation, we found 50% had ceased to be viable. In other words, that one came up right at that critical point. For some reason it got over the hump. These tubes had no rancid fats in them. We know that—which bears out the remarks of Dr. Halvorson. EVAN WHEATON (American Can Company) In regard to Mr. Brissey's question—we ran into the same thing in the luncheon meat, entirely separate packs, where on long storage we got no spoilage, and there wasn't any survival. Apparently, the organisms were non-viable. Of course, they incubated samples. Along the same line, we did some work with thermophilic organisms in vege- tables, and those packs were stored at temperatures below the growth range of the organisms. There we definitely got sterilization with that type of organism. Of course, that wasn't on incubation, and so we can substantiate what you have found there. This brings to mind one question I would like to ask Dr. Williams. Some years ago I think work was done on P. A. 3679 in shrimp. Was it not concluded that the highly-resistant organisms didn't germinate? WILLIAMS That is a general concept. The general concept is that the highly- resistant organism and low-resistant organisms do not germinate in the same way. One is much more resistant than the other. WHEATON I was wondering if this could possibly be tied in—although highly-resistant organisms do not germinate in a highly-resistant medium, they would in a less favorable medium. WILLIAMS I think that might well be. We have a lot of sugar samples which originally were very heavily contaminated with thermophilic spores over a period of about 10 years, essentially negative for any bacterial content; we ran them again. The thermophilic spores had died out in dry sugar—why, I don't know. There is nothing inhibitory there, 71

because there is no moisture for them to grow on. They have just died of old age, I suppose. CLARENCE SCHMIDT (Continental Can Company) I was very glad to hear Dr. Halvorson's remarks about the poten- tial inhibitory effect being against the cell which may have germinated from the spore rather than against the actual germination of the spore because the experiment confirms a point that I had been reach- ing out for from the standpoint of some theoretical considerations. The other point is that we shouldn't, perhaps, consider spores as completely without metabolism during any given time of storage. It is evident that during storage under dry or under somewhat moist conditions—even storage under conditions which would prevent the development of a vegetative cell—a slight metabolism takes place. We might almost say that some slight metabolism must take place to maintain life. This can eventually lead to exhaustion and failure to germinate when suitable conditions for germination are provided. Maybe we need to develop techniques which will define more strictly what we mean by germination. Actually, at the present time, our concepts are being defined by the techniques which we are using to make these determinations. BALL There is a question in regard to microbiology I should like to have brought out. It was dealt with to a considerable extent by Dr. Sugiyama and implied in Dr. Gross' talk; it is a question pertaining to the injury to the cells by heat. I have been wondering whether or not it is accepted generally by microbiologists that such injury ac- tually does take place. Are spores which have been subjected to heat insufficient to completely'inactivate them nevertheless affected to such an extent that they are slow in germinating and perhaps much easier to kill? Applying this to Dr. Gross' work, it would suggest that an experi- ment be tried in which some of the tubes would be prepared with a number of cells, viable according to his culture tests after heating, and additional tubes be prepared into which are inoculated an equal num- ber of fresh spores. Just how that would be done, he could decide, but the objective would be to see whether or not the results from those 2 sets of tubes would be the same in regard to growth after a period of incubation. I would like to throw that question out to any microbiologist just to satisfy my own curiosity. I have understood there was some disagreement, at least, as to whether or not such in- jury to cells does take place and if it has the effect that I have men- tioned. WILLIAMS In supplement to Dr. Ball's question and Dr. Gross' answer, there are a number of papers on the addition of enriching materials to 72

facilitate the germination of heated spores. Dr. Scott from Australia, who was in this country 2 or 3 years back, discussed the addition of starch as facilitating germination of heated botulinum spores. You get much higher germination if you incorporate starch than if you do not incorporate starch, where you are using heated spores. There are, however, several publications on the use of enriching substances, nutrients, in the medium to favor the germination of heated spores over unheated spores. There is definitely an injury. SUGIYAMA Mr. Chairman, along that line, it has been proved many times that spores subjected to rather severe heat treatments are much more fastidious in their nutritional requirements for growth to take place. It would suggest that some of the enzyme system may have been par- tially inactivated as to the form of products necessary for the germ- ination to take place. BALL Also, I suppose they would succumb to unfavorable conditions more readily than the other. CHAIRMAN ROBINSON Dr. Williams, am I right in my concept, not being a bacteriologist, that studies made using isolated organisms inoculated in the natural food products may give false indications as regards thermal proc- essing times and temperatures if it is assumed that they are the same as so-called natural contamination? Now, that's something I have heard for a long time. Is it true that the so-called natural contamina- tion is liable to be more resistant than something that has been trans- ferred? WILLIAMS There is one item that bears on that, Dr. Robinson. The question you are asking really is whether the native versus the college-educated bacteria have a difference. The item which has particular applica- bility, I should say, in this connection, deals with thermophiles rather than the bacteria with which we are most concerned. As early as 1930 Cameron showed that the organisms in sugar had exactly the same resistance. The same organisms isolated out and a spore crop produced on artificial media, had sugar heavily contaminated, and on this heat- resistance studies could be done. You could make up the same concen- tration of spores, produced under heated conditions versus those that came from natural conditions. The resistance was the same, indicating cultivation in the laboratory did not cause an immediate change. Now, everybody who has had experience in heat resistance knows that organisms vary in heat resistance. We have a strain of the 1518 thermophile, which is so well known, in our laboratory; one of my 73

students who is working with that has established its resistance at over 50 minutes at 250°F. But you simply could not kill that organ- ism in any food product and have anything left fit to eat. You would burn the food up. BRISSEY I think we can infer from the papers presented by Dr. Sugiyama and Dr. Williams this morning that some workers have found an in- fluence on thermal resistance of free water versus bound water. We know that we can influence the amount of bound water present. Do we know what the varying types are that are in spores, and do they have a wide range of iso-electric points, for example? WILLIAMS I can't answer that question because I do not know. With regard to bound water, I wonder if Dr. Halvorson wouldn't comment on that because I think he probably knows better than anyone else around here about bound water. HALVORSON We are currently studying a project planned by the Quarter- master Corps on this bound- and free-water question. I would much rather talk about it if I didn't have to use the term "bound water." I think it is a misnomer, dependent on an experimental setup. I don't know myself what it means. I can say this, that if one determines the moisture content and the equilibrium vapor pressure of spores at different moisture levels and of vegetative cells at different moisture levels, we come to the conclusion that the vegetative cell likes water better than the spore does. The vegetative cell is more lyophilic than the spore. The spore is more lyophobic. To illustrate—if we follow a horizontal axis, grams of water per gram of dry substance—against the equilibrium vapor pressure of spores and of vegetative cells we can obtain curves for both spores and vegetative cells. The grams of water per gram of dry substance decrease. Finally, when we have almost perfect dryness we have curves that show the vegetative cells cling to the water better than the spore does. Let me repeat: The spore does not cling to water as well as do the vegetative cells, indicating that the bound water or the affinity of water for spore material is less than for the vegetative cell. Therefore, I think the concept that the water in spores is bound and therefore the spores are heat resistant is false. We have, I think, a better explanation for heat resistance in spores than this concept, and that comes from the studies we made on alanine racemase. This enzyme found in spores is heat resistant—has a heat resistance that is relative to that of the spore itself. The same enzyme found in vege- tative cells is thermolytic. If we subject the enzyme in the spore to sonic oscillations, we can rupture the particle to some extent, and separate from the particle a heat-sensitive portion, an enzyme, and 74

another portion that is heat resistant. If we subject this so treated spore enzyme preparation to fractional centrifugation, we can throw down a fraction at 45,000 G. that is heat resistant. Now, we are just getting into this, and I am talking prematurely. Maybe a year from now we will know more about it. SCHMIDT To add one further comment on this bound water question—I believe this difference between bound water of vegetative cells and spores has arisen from 1 or 2 articles in the literature that report work done by a specific chemical technique which has certain ques- tionable aspects. But, nevertheless, these articles have formed the only source of our discussion; there are continual repetitions, reviews, citations and discussions as to the nature of spore resistance. It is still attributed to the bound water content of the spores. I believe that the question should be investigated either by an attempt to repeat the original type of experiment to show if the method is validly inter- pretable in terms of bound water or to continue the types of experi- ments that Dr. Halvorson has cited. I am very glad to see that whole question opened again. RICHARD I. MEYER (QMFCI) Aside from the bacteriological problems discussed here today, I wonder if any thought has been given to just what can be done with canned meats from a technological point of view. In other words, does the type of cooking in water that they are actually subjected to affect their quality? If you try home methods aside from the can, and you tend to overcook just a little bit, you probably end up with the same mushy, soft texture. My point is this: Has any work been done or been contemplated, using good cuts of beef such as we like to get in the can, properly sterilized, to see if you can really get an improved product in a can if you just relieve the amount of heat—or is it al- most an impossibility because of the conditions under which that product is cooked? TISCHER I can make one comment on that although I am afraid I am in the same boat as Dr. Halvorson: We are still in the process of attempting to provide such information. We work with canned beef without addi- tion of anything, except time and temperature. What we are hoping to do is expand upon the evaluation of attributes, whether they are subjectively evaluated or otherwise, which have something to do with the final acceptability of the product. What we hope to do in partic- ular is to use a setup similar to the one Dr. Ayres described, and I de- scribed later, in mapping out the changes which take place at various processing temperatures and what may be considered the requisite length of time to accomplish a fraction of, all of, or more than the 75

necessary amount of sterilization. Until we get through with that, I can't give you any answer, but at least, I can say there is some work going on at the moment, our own work, which we hope will throw some light on that subject—for just plain beef, of course, not for mixed products. GARDNER Mr. Chairman, part of the answer to the question lies in the economic feasibility of using higher grades of beef. There is another closely related aspect. That is, are we really on the right track when we think overprocessing and overcooking contribute to lesser accept- ability? WINSTON S. OGILVY (Armour & Company) The thing we want to do first is to try to get some idea of the relationship of acceptability of the product, that is, flavor and texture, to the processing that it gets. In order to do this, cooperating indus- trial organizations are going .to make up a product using several processing levels and subject it to taste panel evaluation. CHAIRMAN ROBINSON I have thought for quite some time about this problem of more acceptable canned meats. From the industry's viewpoint, you are aware it is not a very satisfactory business. Acceptability is so low that the volume of product purchased by the American public does not represent a very suitable financial return on the basis of necessary investment. It would be most pleasant for the Armed Forces if you could give everybody a nice piece of roast beef similar to a piece of roast beef they would have left over and prepared as so-called fancy cold cuts, or roast pork, or baked ham. These items taste exactly like the articles as they come out of the kitchen. When you can give them that, you have given them the things they want most, and, of course, we are coming closer and closer to achieving that ideal. Within 2 years we are going to see some of those kinds of products because of the advances made possible by the fundamental knowledge that has been supported by the Quartermaster group and others. We are learn- ing what to do about these spoilage organisms, what different types of heat treatment mean—the sort of thing we heard today. But that isn't the only answer—not everybody can afford to eat cold roast beef, cold roast pork, and cold baked ham. I don't know that the Armed Forces can afford to feed that exclusively; so you have to come back to these so-called comminuted products. I believe there is a great future for them simply by their having a better taste and regardless of whether they have a particularly better texture. All of us all of our lives have used from the best on down the scale—the things that aren't quite as good, but don't cost us as much. We eat them because we can afford them; we eat them for that lunch- 76

eon, for that supper, for that night, for that not quite so fancy meal. My answer is that out of this work for the Armed Forces civilians are going to get 2 new types of products; one, the aseptically canned, first-grade items that are not available today in any sense, and the other, improvement on the sort of thing that we have which won't be equal to them, no matter what you do, but which will be a lot tastier as a secondary type of meat. GARDNER I might add that the Quartermaster has been supporting re- search, to be reported tomorrow, on the use of dielectrics, and we are at exactly that point. We have determined the microbiological aspects, and the next question is: Using controlled subjective methods of evaluation, will the improvement be worth while? I think Dr. Doty will answer that question tomorrow. ROY E. MORSE (Wm. J. Stange Co.) When you discuss canned meats, you inevitably make the com- parison with a nice piece of fresh roast beef. This seems to me to be starting off on the wrong foot. When we purchase a can of peaches or pears, which we have accepted through the years, we no longer ex- pect to compare those with fresh pears or fresh peaches. Why, nec- essarily, do we expect to compare canned meats with fresh meats? They have the additional advantages, which the fresh meats do not have, of being storable in some areas, and at the same time we pay for the quality degradation. I think we should introduce that thinking a little bit into this whole symposium. GARDNER Speaking for our program, that has been taken into considera- tion. Fresh peaches are not available to the consumer for a large part of the year, and for a long, long time they have been sold in the form of canned peaches. The consumer has therefore developed a liking for canned peaches. But meat is available to the consumer the year around in the form of fresh meats or a sausage product or a cured and smoked product. The consumer is therefore less content with a canned product. That's our reason for having a fresh-tasting piece of properly cooked meat as our canned meats goal. F. WARREN TAUBER (The Visking Corporation) I would like to raise this question in relation to these canned products.: Why do the Armed Forces invariably pick the inconvenient sizes and shapes? It seems that frequently they want to cook up some- thing in an odd shaped can. Basically, we run into experiences on the farm where you select the proper size and shape of can and get a fairly decent product out of it, yet it seems that in canning for the Army and frequently for commercial use, they are after a can with a 77

small amount of tin. which seems to be the primary concern. Our ex- perience has been that, in many of the things they want, there is no attempt to consider the problem of size or shape. I was wondering whether that was being given any consideration in the program at the present time. CHAIRMAN ROBINSON I don't know whether Dr. Gross or Mr. Brissey or some of these other gentlemen here agree with you on your original premise that they may not be putting luncheon meats up in the right size can. Let's ask them if they have given any thought as to the best can sizes both commercially and for the Army. TAUBER Both commercially and for the Army—invariably they seem to pick a size because it is better adapted to the tin they are using, not necessarily the right size and shape for the product to be processed. One thing I had in mind, specifically, was canned meat and sausage. For some of these products the commercial grades utilize a little 4- ounce container. The product in this can is in much better condition than would be a comparable product in a I'/j-pound can or greater for the Army. It seems to me the Army specifications call for a much higher quality of material, but in the process of preparing it, it is pretty well chewed up. GROSS I think the Army people will have to answer from their angle. COLONEL WILLIAM JACKSON (OQMG) I have been listening to this discussion with much interest. I was particularly interested in Dr. Robinson's comment—that the civilian thinks of canned meat as an occasional meal. He spoke of it in that sense—that you might have it occasionally as a substitute for a cold supper or dinner. In the Army that is not the purpose of canned meats. When we buy canned meats we buy large quantities as assur- ance that we can feed the soldier in the field under extreme combat conditions where you cannot get refrigerated products. We try to get fresh food there whenever possible, but to do that, we do have to carry large reserves of canned meats, and we do have to eat them. I was in charge of the food program in Japan which supported the Korean operation. Initially, we tried to ship perishable items to Korea, that is, in September 1950. Due to combat conditions and shortages of shipping and the sudden build-up of troops, we were unable to furnish troops with fresh food, and clear through December 1950 they sub- sisted for about 3 months on canned items entirely. The morale of the Army at that time was not good. I don't know how much the food contributed to this, but I know it had a definite effect. Beginning in January, due to the insistence of General Ridgway, we put fresh 78

food up there. It was quickly a rejuvenated Army. However, at the time we did that, food shipments were made at the expense of other items because we had to get something in there to help revitalize the Army. If we can get a good canned meat that you can feed, you can re- duce the expense to the taxpayer. You can reduce the spoilage losses that the Army has to sustain in the field. We made another test quite recently of the small cans of meats which are in the C Ration. Most of them are mixtures with vege- tables, but even there, when we placed troops on a test for 30 days and gave them nothing else to eat, under controlled conditions, where they couldn't get any other items except what we might give them, they got to the point—after 10 days—where they didn't want to eat at all. Their acceptance of food dwindled to the extent that it im- paired their health. They couldn't work; they didn't care. That is basically why we are interested in getting a good meat item in the can for the Army or for the Air Force or Navy. It is perhaps an emergency item, but it is an extremely important one. It is also the only item you can ship when you have an immediate mobilization of the Army in the field. You haven't refrigeration. You are busy with all the other factors in combat, and you must have an item that the troops will eat and enjoy. Meat is still about 50% of the ration; frankly, the canned beef, canned pork, and the various substitutes or mixtures that we have all seen taste the same after you eat them about 5 days, and if you don't believe it, any one of you put yourself on that diet for 5 to 10 days and see what you think. The old items we had—hash and meat and vegetable stew and some of those items— all taste the same. You can't tell whether you are eating a piece of potato or a piece of meat, actually, after it is stored for about a year, and most of the items that we issue are 2 years old when we issue them. They are not fresh because we have to buy them and keep enor- mous reserves at various strategic locations. Unfortunately, they often just sit there. If the items were acceptable, or had greater ac- .ceptability than at present, we could inject more of them into the daily ration and our turnover would be much more rapid. We do feed it to all troops in the Army, Air Force, and Navy at the present time by direction. I think in the Far East Command they eat about 7 meals of canned meats a month, but it doesn't set very well with the soldier. He doesn't know why he has to eat it because he doesn't like it. In many cases he just kind of half skips that meal. We have to find something, when we are using soldiers in the field. We have to keep them full of pep and energy, and the only way you can do it is to give them food. Canned meat is an extremely important problem to the Armed Services. If you ever develop canned meats that are really highly ac- ceptable to the soldier, he will change the tastes of the civilian market because he has done it in other wars when he came back. He changes 79

the habits of the American people because he likes certain items, and when he comes back he demands those items. Canned meats are not a highly profitable item, I have been told, by the various canners, but I think that is the problem that we have to solve—not to make profits but to get a better product. CHAIRMAN ROBINSON Colonel Jackson, we are in perfect accord with what you have said. I actually went on a fishing trip 2 years ago and bought all kinds of canned meats I could get. It took me only 2 days to find out they all tasted alike. In the meat industry we are absolutely non-complacent about our canned meats. They are not good; we recognize the fact that if we could give you in the Armed Forces an acceptable product that the soldier could, when essential, eat day after day, on that day we would have arrived also in the civilian market. Today we are spending millions of dollars in the industry on all these processes that you will hear about tomorrow. COLONEL JACKSON I know you are, and that's the purpose of this discussion. I didn't imply the industry wasn't doing a great deal. You are, and the uni- versities are doing a great deal, and we are doing, actually, a very small portion in the total over-all picture. We hope to expand our activity in this field; it is a very large problem for the Armed Serv- ices. It is a problem, I think, which is going to be with the Armed Services indefinitely. It isn't anything you are ever going to whip immediately. I think the effort spent on canned meats is well spent. It is a good investment for the American taxpayer and the American public. GARDNER Mr. Chairman, I might get back to the original question on con- tainers for the purpose of illustrating how the information brought out in this symposium and the one that meets tomorrow is going to be of benefit to us. Mr. Smith is going to tell us something about what he and Dr. Ball have done. The process they have worked out would, if it bears out its promise, save the taxpayers of the United States $160,000 on containers alone. CHAIRMAN ROBINSON We have time for 1 or 2 more questions. CARL S. PEDERSON (New York State Agr. Exp. Station) Df. Dack, Dr. Sugiyama, Dr. Williams, and, I believe, Dr. Hal- vorson have been studying the relationship of the various factors of spore germination and spore formation and heat resistance of spores. I am wondering if they have given any thought as to whether some of these same factors may be effective in these new types of processing. 80

That is, in regard to electron bombardment and radiation and so forth, whether any thought has been given to whether the same factors will hold true in those new methods of processing. It is entirely theoret- ical, I suppose. SUGIYAMA Actually, we are trying to run a concurrent set of tests with cobalt 60 radiation, to see if the factors increase or decrease the heat resistance of the spores or in some way affect the susceptibility of the spores to that radiation. WILLIAMS I have thought about it a little, but not long enough. I haven't formed an approach to the problem yet. I certainly believe that it very much deserves attention. DACK One thing is true—it takes more reps to kill the very heat-resis- tant organisms than it does some of the vegetative cells; and another thing, the amount of heat it takes to kill such organisms deteriorates the quality of the product, very often leaves you an inferior product. Flavor and color are anything but acceptable. I think that's in line with your experience, too, isn't it, Dr. Robinson? CHAIRMAN ROBINSON That's correct. BALL This is not so much a question as a comment. Colonel Jackson's remarks on canned meat acceptance made me wonder whether or not there would be a question of nutritional quality involved. His remarks seemed to me to indicate that the soldiers will eat until they reach the point of disinterest or not caring. I always associate such an atti- tude with improper nutrition. Should we be considering the nutri- tional qualities of these products as well as the organoleptic quality? Possibly after they live on these particular types of foods for a while, they do lack some of the nutritive elements they ought to have had. COLONEL JACKSON The Surgeon General has been conducting some tests on that in conjunction with the Quartermaster Corps; they have been a little shocked at the loss of nutritional quality of these meats. In the ex- periments I made we ran only a couple of actual controlled experi- ments with troops. The meats were quite old, and the nutritional loss was quite substantial. They are going to make a much more thorough study of the problem now because nutrition is definitely involved; the loss of nutrition is quite great. CHAIRMAN ROBINSON Thank you all for coming. It has been a very nice meeting. 81

IV. Canned Meats of Today WEDNESDAY MORNING SESSION April 1, 1953 The meeting convened at 9:15 with Dr. Clarence Wiesman, pres- iding. CHAIRMAN CLARENCE WIESMAN Yesterday we had a very interesting session concerned with the microbiology of canned meats; later, the discussion turned to heat- transfer problems connected with processing of canned meats. Today we will discuss first of all something about the canned meat situation as it is today, something about what the Army would like in canned meats; the papers will be concerned with new methods of processing designed to get away from some of these problems that have caused the symposium to be called. Actually, in looking over the program and in listening yesterday, it occurred to me that perhaps the word symposium isn't really a good description of the kind of program we have had here. To me it is really a short course in can- ning. I know I have gotten a lot out of it so far, and I am sure every one here will have learned much about canned meats before this is over. This is an unique type of symposium in that we haven't invited any one here to be a listener. Every one here is invited to be a partic- ipant. Later on this afternoon we are going to have a round-table discussion, and we would like everyone in the audience to participate in this discussion, not only from the standpoint of asking questions, but also from the standpoint of contributing information that might be helpful to the problem. The next speaker, Major William B. Levin, assistant chief, Mili- tary Operations Office, Quartermaster Food and Container Institute, formerly was an infantry officer and served in the European, Pacific, and Korean theaters. He is well qualified, obviously, to explain "Why We Need Better Canned Meat Products." Major Levin. Why We Need Better Canned Meat Products MAJOR WILLIAM LEVIN The obvious reasons why any ration item should be improved are: (1) to increase the acceptability, nutritional qualities, and stability; (2) to add interest to the diet of the soldier; (3) to improve the lot of the fighting soldier. These reasons are generally known and accepted. It is my hope to furnish you with a picture of how our troops are sup- lied with food in Korea, how they are disposed on the ground to form 82

a typical fighting unit, and how they are fed under combat conditions. You will then be able to see the part that foods play in combat opera- tions—and why, among many other subsistence items, it is vital to have the ultimate in the canned meat items. The ration distribution pattern in Korea. With regard to how food is dis- tributed down to the front line elements of an infantry division, let us consider in broad outline the arrangement of the troops on the ground. A normal infantry division consists of approximately 18,700 men and officers. However, in Korea an infantry division usually has several attached units, and therefore its strength generally exceeds this number. A division in combat usually is spread out into 4 operating echelons. The echelon closest to the enemy—where the heat is on—is called the outpost or the Operational Line of Resistance. This echelon is there to intercept a surprise attack on the main forces which are located on the Main Line of Resistance and to divert the attack or break it up. You can readily see that these units must be on the alert 24 hours each day. Since this echelon is in direct contact with the enemy, to get the food to them takes planning and maneu- vering. The problem is complicated by the fact that it is Army policy to serve hot meals to the soldiers whenever possible. In Korea, where we have endeavored to supply at least one hot kitchen-prepared meal to the soldiers on this Operational Line of Resistance each day, it must be brought to the troops during the hours of darkness. The other 2 meals consisting of packaged operational rations, con- taining canned meat items, are less difficult to supply and can be carried, in some instances, on the soldier's person. The bulk of the soldiers of a division are found on the Main Line of Resis- tance. In Korea, it has generally been possible to serve at least 2 hot meals each day to troops on the main line. However, as in the case of the Operational Line of Resistance, we are again confronted with the problem of preparing the food, transporting it, and seeing that it reaches the soldier in a hot, palatable condi- tion. Food for the main line is prepared at unit level in infantry company kitchens. It is possible here to use field ranges and to distribute the food directly from the kitchen to the individual soldier. Meals are fairly well regularized at this point and no need ordinarily exists for delivering the meal under darkness or other unusual circumstances. The soldier on the Main Line of Resistance usually gets 2 hot meals a day; the soldier on the Operational Line of Resistance gets a maximum of one hot meal a day. The operational C Ration is used for the other meals. It is an interesting fact, sometimes overlooked, that soldiers on the Oper- ational Line of Resistance, who must maintain a 24-hour alert, require more than the usual 3 meals a day. Their expenditure of energy is greater and food, of course, under some circumstances, can relieve tension. It has therefore been found necessary to supplement OPerational Line Resistance feeding with an addi- tional meal, usually during the evening or during the night. The Individual Assault Pack, which is not a complete ration in itself, has been used for this purpose. This ration centers around canned meats and it might be said that: regardless of the soldier's location, whether on the Operational Line of Resistance or the Main Line of Resistance, whether his food is served hot or cold, the food he eats is processed food, usually in the form of canned foods. It is therefore essential that it be appetizing, continuously acceptable if possible, and nutritious. Canned meats fulfill these requirements rather well, but there is certainly room for further improvement if we are to meet these requirements adequately. Behind the troops on the Main Line of Resistance, there are other division echelons extending in some cases as far back as 30 miles. With standard Army policy to serve hot meals to the soldiers whenever possible in mind—here we find the ideal situation. It is possible under present tactical situations in Korea to serve 3 hot meals a day to the service elements of an infantry division. These elements include the engineers, ordnance, and signal troops which have head- 83

quarters back of the Main Line of Resistance. The normal, field-type kitchen is used here. The food served does not differ markedly from domestic garrison feeding. The fourth operating echelon of an infantry division in Korea, the very rear of the division, usually is spread over several miles, and its soldiers are fed in a consolidated mess. This has been found to be necessary since replace- ment soldiers and numerous other soldiers are constantly being processed through this area, both to and from the front elements of the division. The consolidated messes usually serve 500 to 1,000 soldiers cafeteria style. These messes are estab- lished on a semipermanent basis and often have dishwashing equipment and more elaborate serviner facilities than is possible closer to the J'ront. From this brief review, it can readily be seen that the difficulties in feeding an infantry division increase as one approaches the front elements of the division. Troops up to the Main Line of Resistance are served from the field kitchens with 3 hot meals daily. Troops on the Main Line of Resistance usually have been able to receive 2 hot meals daily and must use a packaged operational ration for the other meal. The troops on the Operational Line of Resistance sometimes receive more than one hot meal per day, usually receive one, but in many instances must use a packaged operational ration for all 3 meals. To win battles, the soldiers in any army must be properly supplied. Food is the fuel that powers the soldier and as such it needs a high "octane"—or fuel value—just as does a motor fuel. It behooves all of us, whether we are in the Military Service or in civilian occupations, to do all that we can to see that the food we supply our soldiers on the firing lines is the very highest in quality and better, if possible, than that eaten under happier circumstances. It can never be said too often that if rations are not appealing, they may not be eaten, and if they aren't eaten, their nutritional value is nil. Moreover, wastage of food means that time, effort, and the money expended in manufacture and supply have been nullified. Add to these factors the further one that rejected rations are a source of disgruntlement and low morale, and few will dispute the generalization that if soldiers don't eat their rations, their effectiveness in battle is lowered. Canned meats in relation to morale. Canned meat products are of prime importance in combat rations. These products are central to the ration, and upon them the effectiveness of the ration as a whole depends. If it were possible to achieve the ultimate—a canned meat that even after prolonged storage tasted like fresh, it is likely that all other items in the ration would have added appeal. You, as scientists, often use that expensive word—synergism—which means the con- junction of 2 qualities that, added together, more than exceed the ef- fect of the mere sum of the 2. Thus, when we arrive at the ideal can- ned meat we can perhaps consider that this one basic improvement will produce an over-all acceptability for rations greater than would normally be expected by this improvement of only one item. With canned bread now a reality we may be able to supply—when we at- tain the perfect canned hamburger—the perfect hamburger sand- wich! You will realize, of course, that I am using this example only by way of enforcing a point. We seek the ideal but realize that we must be content with the improved—that is, with a way point toward perfection. During World War II and during the Korean conflict, many new and highly satisfactory canned products were developed and proved to be suitable for ration use. Field reports still emphasize, however, 84

that continued use of even the present improved canned meats leads to monotony, with an accompanying reduction in acceptance. The search for methods of eliminating these deficiencies is still necessary, and we must turn to your group for real improvement in canned meat items in future military rations. Perhaps, by furnishing you with a brief glimpse of combat feeding, I have indicated the great value of your past efforts and the continued need for further advances. V. Potentialities of New Methods of Manufacturing CHAIRMAN WIESMAN Thank you very much, Major Levin. I am sure that your paper has helped give us all a better understanding of the problems of feed- ing the Armed Forces. The next paper will be presented by Mr. Horace L. Smith, Jr., consulting engineer and co-author of the famous Smith-Ball process. Mr. Smith is going to describe the potentialities of pressurized manu- facturing facilities for producing canned meat products. Mr. Smith. Potentialities of Pressurized Manufacturing Facilities for Producing Canned Meat Products HORACE L. SMITH, JR. In this discussion on sterilization of canned meat products the destruction of pathogenic and spoilage organisms by heat alone will be considered. There are other processes under investigation that are directed toward sterilization methods that do not involve appreciable increase in temperature of the product, but this line of work is being left to other investigators. It is assumed that high-temperature, short- time processing provides the means for producing the most desirable method of sterilizing meat products. In order to reduce the time of processing to minimum practical values it is necessary to consider temperatures much higher than the boiling point of water at atmos- pheric pressure. In the past, this requirement has necessitated sealing the product in pressure-tight containers before sterilization, and then subjecting the sealed containers to the conventional high-pressure steam retort procedure. The disadvantages of this process are ob- vious and need not be elaborated. A specification for the ideal process would require all of the product to be heated uniformly in the shortest possible time. In con- sidering canned meat products we are dealing with discrete particles as distinct from homogeneous or liquid products. In considering the means of securing rapid and uniform heating of these discrete par- ticles, the physical dimensions of the particles or pieces of meat play an important role, and also the environment in which the products 85

are heated is equally important. If it is necessary to heat the product to temperatures in excess of 212°F., it is essential, since all of these products contain moisture, that the heating process be carried out under pressures greater than atmospheric, otherwise the higher tem- peratures could not be reached. In considering available means to secure rapid heating of the product, 3 basic methods offer possibilities. If the largest discrete particle is of small dimensions, it is possible to secure satisfactory heat transfer by simple conduction from a heated surface. A product of the consistency of hash or chili con carne could be heated at a satis- factory rate if spread out in a very thin layer or film on a heated sur- face. As the size of the particles increase in dimension, heating by conduction from one surface is not fast enough to satisfy the criteria specified. An increase in the rate of heating can be provided by sur- rounding each separate particle by an atmosphere of steam at a tem- perature higher than the temperature required at the center of each particle. This method also relies on conduction from the surface to the center of the particle; therefore, as the dimensions of the particle in- crease the time also increases. A 3rd and very promising method of heating immediately suggests itself, and that is by means of internal molecular friction within the product itself. This method is some- times termed diathermy, electrostatic heating, micro-wave heating, etc. The basic concept of the methods previously outlined require con- ditions that will permit heating of low-acid food products to tempera- tures of from 240° to 260°F., and the filling of products at these tem- peratures in open containers. To achieve this requirement, the so- called Smith-Ball pressure canning process was developed. It is based on the physical law of vapor pressure. We know that water boils at 212°F. at sea level under normal barometric pressure, and that on the top of a high mountain the boiling point is lower. Conversely, as the pressure over the water increases, its boiling point increases. At 20 pounds gauge pressure water will not boil until it reaches 260 °F. The Smith-Ball process consists of a room or building of steel plate designed to withstand internal pressures in excess of the highest pressure expected to be used. In this room is located all of the equip- ment needed for the processing or heat sterilization of the product, conventional filling and closing equipment and means provided for at least partially cooling the containers in the pressurized space. The normal complement of operating personnel would work in this space, performing the same duties required in a more conventional canning plant. With the suggestion that people work at an elevated pressure, the question immediately arises as to the effect of the higher pressure on the human body. Fortunately, there is a great amount of data available on this point. All of the railway and vehicular tunnels built under the Hudson and the East River in the New York area were con- 86

structed by means of the compressed-air shield method of tunneling. "Sand hogs" worked under compressed air for long hours and engaged in strenuous physical effort. The Bureau of Mines has collected statistical data on this subject and the record shows that of a total of 809,838 decompressions from pressures up to 22 pounds gauge, only 16 cases of compressed air sickness resulted, and all of these were trivial. This 22-pound pressure corresponds to approximately 263°F. Several high-pressure wind tunnels are in operation in this country. The marine diver is normally subjected to pressures much greater than 22 pounds—to pressures, in fact, as great as 265 pounds gauge pressure. This is equal to an open sea dive of 561 feet. The latest U. S. Navy Diving Manual issued by the Navy Department, Bureau of Ships, July 1, 1952, specifies from 4 to 6 minutes decompression time for a diver working approximately 4 hours at a depth of 50 feet, which corresponds to a pressure of 22.3 pounds gauge. It can be definitely stated that with exercise of reasonable care there is no in- dustrial hazard involved in working at pressures of the order of 20 pounds gauge. The application of the Smith-Ball process to meat products such as hash, Vienna sausage, frankfurters, luncheon meats, hamburgers, and any other type of meat products that are of relatively small dimen- sions in at least one direction, can be quickly heated to acceptable temperature values by means of heat exchangers designed to the physical requirements of the products, by surrounding the product with steam, by cooking in water or high-boiling liquids such as cook- ing oils, etc. The heating of the product can be carried out either exterior to the pressurized chamber or within the chamber. The con- tainers and ends can be pre-sterilized by means of steam. When steam from a high-pressure source is allowed to flow into a compart- ment or enclosure within the pressurized space, the temperature of the steam corresponds to the pressure maintained within the chamber, therefore with 20-pounds pressure the temperature of steam avail- able for sterilizing the containers and ends would be 260°F. High frequency heating. In dealing with meat products of larger dimensions, such as shoulders, hams, fowl, or any other large piece of meat, heating by conduction from the surface to the most remote point may require a time greater than is compatible with maintenance of product quality; therefore the use of heat- ing by means of molecular vibration appeared to hold great promise. Considerable commercial success has been achieved by a number of manufacturers supplying electrostatic heating equipment used in heating non-electrical conducting materials such as wood, paper, pre-forms for the molded plastic industry, synthetic fibers, and a long list of other products. Special applications of this basic process have also been used to cook foods, especially meat products. The early work done in the use of high-frequency heating was in the relatively long wave-length band, in the range from 2 to 20 megacycles. As this art developed, it became apparent that better results were obtained with the shorter wave lengths, which meant higher frequency. With the rapid development in the entire field of electronics, equipment has become available that operates at much higher frequencies. In the patent literature on this subject it is stated that the best results are obtained by using a frequency corresponding to a wave length that approaches at least one 87

physical dimension of the article being heated. If we assume that 10 cm. (approx- imately 4 inches) is a desirable wave length, this corresponds to a frequency of 3,000,000,000 cycles per second. Electronic heating could be on a batch basis or a continuously moving conveyor carrying the material through the high-frequency field. The details of high-frequency heating would have to be worked out to fit the requirements of a specific product or group of products. Pressure chambers. Pressure chambers suitable for use with the Smith-Ball process would be built to satisfy local codes and to fit in available space. One method of constructing an inexpensive pressure chamber is to build the chamber in the shape of a horizontal tank. Taking an arbitrary size, 22 feet in diameter and 70 feet long, the chamber could have 2 work decks or floors and would provide approximately 2,400 square feet of usable floor area at a cost of between $6.00 and $8.00 per square foot. This cost is comparable to the cost of a plain first- class multi-story plant. The pressure chamber could be located outside of exist- ing buildings, possibly parallel to a wall of the building, with an airlock and communicating means through the side of the tank or through one end. The upper deck could be used for product heating, pre-sterilization of containers and ends, filling and closing equipment; the lower deck could be used for can-cooling equip- ment. A cylinder is inherently stable for internal pressure; therefore, relatively light construction could be used with the usual factor of safety complying with the American Society of Mechanical Engineers' code for unfired pressure vessels. As floor drains are necessary in practically all canning operations, the space between the bottom of the cylindrical shell and the underside of the lower deck could be used as a sump or catch basin to accumulate and store floor drainage run-off. This accumulation of waste water could be continuously discharged by means of a float-control drainage valve or the water could be accumulated batch- wise and a manually-operated valve used to discharge the water after the pressure in the chamber had been relieved. Where physical plant arrangement permits the addition of the pressure chamber outside of present buildings, it is the equivalent of adding additional floor space in the form of the pressurized chamber but at a cost comparable to regular plant cost on a per square foot basis. Operating procedures. Empty containers can be continuously valved into the pressure chamber by means of rotary pocketed valves similar to those used on continuous pressure cookers. The cans would be conveyed through an enclosed space filled with live steam, thereby pre-sterilizing the cans before they reached the product-filling equip- ment. The can ends can be pre-sterilized by providing a simple addi- tional device on the closing machines to space the ends in order that steam may reach all surfaces and to provide a short time delay for the ends in this steam-filled chamber. After the cans are filled and closed, there should be a short hold- ing time at the filling temperature. If an occasional viable micro- organic spore is present in the head space, the holding time will insure its destruction. Although the air supplied to the interior of the pres- sure chamber is presumed to be sterile, there is always the possibility of viable microorganic spores being released from the person of the operator, from the surface of can covers before they enter the steril- izer, or from the surface of the can valves. After the short holding time at filling temperature, the cans are cooled to a degree that reduces the internal pressure to a value that would not cause undue stress in the containers when passed out to atmospheric pressure. If there is any head space in the container, and if cold water is sprayed on the 88

can, condensation of the water vapor within the head space imme- diately occurs, thereby reducing the pressure within the container. This, in turn, causes boiling or evaporation of additional moisture. As the only source of latent heat to provide evaporation of additional moisture is obtained from the sensible heat of the product, rapid cool- ing occurs throughout the product so long as condensation occurs in the head space. In using glass containers it may be desirable to carry out the cooling within the pressurized chamber to a much greater degree than would be necessary for tin containers. It is entirely practical to do all of the cooling within the pressure chamber. The cooled or partially cooled containers are passed out of the pressure chamber by means of rotary pocketed valves similar to those used in passing the empty containers into the pressure chamber. In any canning operation involving filling of a hot product there is always considerable water vapor or loose steam being liberated around the equipment. In the pressure chamber the most practical way to remove this steam is by means of well-designed hoods connected by suitable ducts to a suction fan whereby the steam can be condensed by means of cold water spray. The air is then passed through a steam or hot water reheat coil to reduce the relative humidity and increase the dry-bulb temperature to optimum comfort level. Fresh air is continuously introduced in quantities sufficient for ventilation pur- poses and the air supply is passed through a sterile filter before being discharged into the pressure chamber. The excess air is continuously valved out of the pressure chamber by means of simple control instru- ments that can be set to maintain any predetermined pressure within the chamber. In order to sterilize the pressure chamber and all of the equip- ment contained therein it is very simple to locate all electric motors on the outside of the chamber and provide packing glands or stuffing boxes for the several shafts where they pass through the wall of the pressure chamber. All electrical controls for the several motor drives are located within the chamber and a simple method of protecting the electrical equipment is to have pressure-tight boxes or cabinets in which are located all push-button starter switches, telephone connec- tions, etc. Prior to steam sterilizing the chamber, the cover of these boxes is secured by means of wing nuts, the cover being made water- tight by means of a simple rubber gasket, thereby protecting all of the electric control equipment. Visibility within the chamber is easily provided by means of plate glass portholes, usually circular and from 8 inches to 10 inches in diameter. The usual construction is to have 2 separate pieces of glass, each separately gasketed. If from any accidental cause one of the glassses is cracked or broken, the remaining glass will be adequate to withstand the pressure and prevent sudden release of the air from the chamber. These portholes provide excellent visibility either from without or from within the chamber. 89

Personnel entering the airlock or entrance vestibule can be brought up to operating pressure in a very short time, the only limita- tion being a slight discomfort if the Eustachian tubes are abnormally small or inflamed or irritated by a head cold. If the pressure changes too rapidly for equilibrium to be established in the inner ear through the Eustachian tubes it is simply a matter of personal comfort to de- crease the rate of pressure change. Going from atmospheric pressure to 20 pounds pressure can be easily accomplished in 2 minutes. De- compression can be regulated manually or by a simple control in- strument having a preset schedule to provide any rate of decompres- sion desired. The standard Navy diving procedure is to make rapid pressure changes to a lower value, then hold the pressure at this value for a definite time, then again a rapid decrease in pressure. The time required for decompression is a function of the higher pressure and the length of time that the operator is exposed to the higher pressure, but in no case would decompression require more than 6 minutes from a 20-pound chamber pressure. Additional advantages. It should be clearly understood that al- though the Smith-Ball process has been built in commercial size, it has not been used in combination with high frequency product heating. The combination certainly offers interesting possibilities, and the technical problems involved at the moment do not appear to be in- surmountable. Additional advantages of the process are: a. The entire processing equipment can be kept in practically sterile condition because at the end of a day's operation the entire pressurized room can be flooded with live steam, thereby sterilizing not only all of the equipment but the ceiling, floors, and everything within the enclosure. b. The air continuously introduced for ventilation purposes is sterile. c. Conventional closing and filling equipment can be used, and as this equipment is further refined and developed, improved machines can be installed whenever desirable. d. By means of pre-sterilizing and filling at sterilization tempera- ture, dry packs can be obtained because the process does not require a liquid-filled can in order to secure heat conduction within the container. e. With the use of high-frequency equipment within the pres- surized space it may be possible to use higher voltages between the treater electrodes due to the greater insulating effect of the denser atmosphere. f. The process does not rely on aseptic filling, as the product is filled at sterilization temperatures; furthermore investigations during the past 10 years have conclusively proved that with a decrease in the number of organisms present the severity of the process can be decreased. 90

CHAIRMAN WIESMAN Thank you very much, Mr. Smith. I am sure your paper will pro- vide many questions for the panel discussion this afternoon. Our next speaker will be John P. Bolanowski, who is manager of the pilot plant of the Girdler Corporation of Louisville, Kentucky. Mr. Bolanowski. Potentialities of Utilizing a Continuous Type of Process in Conjunction with Aseptic Canning for Production of Canned Meat Products JOHN P. BOLANOWSKI Although the approaches to a discussion such as this are num- erous, it is felt that the potentialities of this method of canning some types of meat products can best be illustrated by attempting to bring to light the prerequisites of the process and the problems involved in fulfilling these prerequisites. This will be done by presenting in brief: the definition of the combined process; the equipment required; heat transfer and flash sterilization; the advantages of flash sterilization and aseptic canning. Definition of the process. Simply stated, the continuous, high-temperature, short-time food sterilization in conjunction with aseptic canning is a process which enables the separate and independent but synchronized and concurrent steriliza- tion of the product, the container and cover, aseptic filling and sealing. The work reported by Ball gives a lucid demonstration of the merits obtained with high- temperature, short-time sterilization and aseptic canning. The flash sterilization and aseptic canning process differs from the conven- tional retort operations in that the product is rapidly but separately sterilized and cooled before being sealed in the container. Sterilization of the food material is attained by pumping it successively through heating, holding, and cooling sections of a closed, continuous-heat-exchanger system under pressure." In summary, the procedure for high-temperature, short-time sterilization consists of 4 continuous but separate operations executed concurrently in a closed system, as follows: a. The product is continuously sterilized under pressure at a high temperature (280°-290° F.) by pumping a high-velocity stream through a heat-exchange system consisting of heating, holding, and cooling sections. b. The containers and covers are sterilized by exposure to superheated steam or other hot gases at a temperature of 400°-600° F. for a time sufficient to sterilize. c. The cold (50°-90° F.) product is filled continuously into the sterile con- tainers in an atmosphere kept sterile by 400°-600° F. superheated steam. " One type of heat exchanger which has proved very satisfactory for the sterilization operation is manufactured by the Girdler Corporation of Louisville, Kentucky, and sold under the trade mark, "Votator." Depending on the product, the operating pressure will be 100 to 200 p.s.i.g. in a Votator heat-exchanger system. Pressures of over 2,000 p.s.i.g. have been recorded when using coil-type or tubular-heat exchangers on products such as purees, dog food, potted meats, cream- style corn, concentrated soups, etc. Although pressure is required to prevent flashing, this pressure need not exceed 200 p.s.i.g. 91

This, in the case of meat products, eliminates oiling off or fatting off in the can. d. The container filled with cold sterile product is sealed with a sterile cover in an atmosphere continually kept sterile by superheated steam. Equipment required for flash sterilization and aseptic canning. Sufficient research and process development has been accomplished to permit definite speci- fication of the equipment required. To accomplish flash sterilization and aseptic canning, 5 important equipment requirements must be fulfilled: a. A pumping system capable of pumping a wide variety of products through the heat-exchanger system at a constant flow against a pressure sufficient to prevent flashing. In addition, this pumping system must not damage the product or cause the discrete particles to lose their identity as, for example, creamed beef or cream-style corn. b. A continuous heat-exchanger system capable of very rapid heating and cooling under non-flashing pressure only. In addition, the heat-exchanger system must not alter the identity of the product by mechanical and physical breakdown of the product. The heat exchanger must be so constructed as to operate with a minimum of burn-on, bake-on, and caramelization. c. A holding section to insure each singular portion or particle equal, controlled exposure to the sterilization temperature, so designed that it will not impose excessive pressures across the heat-exchange system. The holding section must also be capable of maintaining the sterilization temperature, preferably by insulation or jacketing. d. A means of maintaining a sufficient back pressure in the heat-exchange system to prevent flashing. The pressure-maintenance means must operate under sterile conditions without pulverizing or comminuting the product— such products, for example, as dog food, creamed chipped beef, cream-style corn, or chili without beans. e. And last, but certainly not the least, an apparatus which is capable of con- tinuously sterilizing the cans and the covers, and is also capable of filling and closing under sterile conditions. Heat transfer and flash sterilization. It must be thoroughly understood that all the equipment discussed is equally important and equally essential to make flash sterilization with aseptic canning a possibility. Individual perfection of any one item is meaningless without an equally perfect functioning of the other items of equipment. Nevertheless, as in all processes, although no one item is most im- portant, there is invariably one part that must be capable of compensating for variables in the process. In this case, due to the numerous types of food products that are adaptable to aseptic canning, it is the heat-exchanger system. To put it another way; in most of the work done, our experience has been that the cans and lids with proper liners and compounds can be readily sterilized, the product can be pumped, and a suitable holding section and means of applying back pressure can be attained. The important question is: Can the product be sterilized without deleterious effects? Advantages of the Votator type of heat exchanger. Several years ago the development work on the high-temperature steriliza- tion of food products was undertaken by the Votator Division of the Girdler Corporation because it was felt that due to the design and the principles of the Votator scraped-surface heat exchanger, the proper type of flash sterilization could be attained for a wide variety of foods. There are several characteristics of this type of heat ex- change which indicated that it would be effective in flash sterilization. These characteristics were well known, for a considerable amount of 92

work with products ranging from the very fluid, such as dairy prod- ucts, to the very viscous, such as dog food, potted meat, and creamed beef, has been done in the past. From this work it has been established that the heat-exchange system for high-temperature, short-time sterilization of food products must have several definite requisites. The heat exchanger under discussion provides these requisites and in many cases affords some unique advantages, as follows: a. The high ratio of heat-transfer surface to the volume of material treated fulfills the requirement for a very high heat- ing rate. b. The constant and rapid cleaning of the heat-transfer surface (1000 to 1400 times per minute) prevents scorching and local- ized overcooking, in the case of heating, or frozen film forma- tion in the case of chilling and freezing. c. Turbulence is created by the revolving shaft and blades rather than by forcing the product at a high velocity through small- diameter tube exchangers, thus eliminating the necessity of building the heat exchanger to withstand high pressures. As a matter of fact, the pressure drop across this exchanger is so low that additional pressure has to be imposed by a back- pressure valve in order to operate at a process pressure more suitable to the product. d. The low-pressure drop across the system eliminates the need for high-pressure pumps. e. Because of the spinning shaft and blades and the flexibility of pressure adjustment across the heat-exchanger system, the equipment lends itself to the processing of a wide variety of food products irrespective of a wide range of viscosity and consistency. f. By proper design of the shaft and control of the annular space, products containing discrete particles have been successfully processed, as for example, cream-style corn, dog food, creamed chipped beef, cream of mushroom soup, etc. g. In respect to sanitation, the heads and shaft are readily ac- cessible. All surfaces coming in contact with the product can be visually inspected. In short, this type of heat exchanger has been proved to be ideally suited for application where the material is heat sensitive, very vis- cous, or undergoes a change of state during heating or cooling. Ex- amples may be found in starch cooking and cooling, gelatin cooling, freezing of concentrates, chilling and plasticizing of fats and oils. The commercial size of the equipment referred to has been em- ployed in pilot-plant and semi-commercial operations in conjunction with 2 types of aseptic canning and closing devices. The pilot-plant tests were conducted with: 93

a. The HCF unit developed by the American Can Co., Maywood, Illinois, and b. The Martin aseptic-canning unit developed by the James Dole Engineering Co., Redwood City, Calif. Both of these companies collaborated on the test projects with bene- ficial and useful results. At this time we come to the point where it is appropriate to ask: What are the potentialities of utilizing a continuous type of process in conjunction with aseptic canning for the production of canned meat products? Over the past 3 years a number of meat products have been flash sterilized and aseptically canned at Louisville, Kentucky. The process consisted of heating from approximately 160° to 285°-290°F., cool- ing to 90°-100°F., filling and closing aseptically, using a combination of Votator heat exchangers and the Martin aseptic-canning system. The products were: potted meat, dog food, creamed beef (hamburger meat), creamed chipped beef, and liver soup (baby food). The work on various other types of meat products is now being carried out at the Votator pilot plant in Louisville. Development at this time is being concentrated on products such as Braunschweiger, deviled ham, pureed liver, beef, etc. Because these products do not include a carrier such as starch, in the case of dog food, creamed beef or gelatin bearers, as well as in the case of potted meat, the heat- sterilization problem is more complex. In conclusion, a report on the potentialities of high-temperature, short-time sterilization would not be complete without a statement and review of the system's advantages. The most important of these are: a. A better flavor, texture, and color are produced with the flash- sterilization method. b. The flash-sterilization method, with aseptic filling and closing, provides a very wide range between scorching of the product and sufficiently safe sterilization, thus permitting a large factor of safety without sacrificing quality. c. Regardless of container size, the quality of the finished prod- uct is the same. d. Product sterilization in a continuous heat exchanger or a con- tinuous pressure cooker allows very accurate control and measurement of the product temperature during the proces- sing. 94

CHAIRMAN WIESMAN Thank you very much, Mr. Bolanowski. Our next paper relates to dielectric methods of heating for the production of canned meat products; it will be presented by Dr. D. M. Doty of the American Meat Institute Foundation. Effectiveness and Potentialities of Dielectric Methods of Heating for the Production of Canned Meat Products D. M. DOTY Conventional steam-retort methods of heating for processing canned meat products tend to overheat the material near the outside of the container before the meat near the center of the container has been heated enough for effective preservation. This results in the typical overcooked flavor and poor texture of many canned meat prod- ucts, particularly those processed in large size containers. To overcome these disadvantages, several new techniques have been proposed and are being investigated in several laboratories. These include processing with intermittent heat treatment, continuous- type processing used in conjunction with aseptic canning, "cold" sterilization using 0 or ? radiation from fission products or electron bombardment, and high-frequency dielectric-type heating. This paper will present the results of experimental studies on the last-named method. Although dielectric heating has not been applied widely for heat processing food products, the method has been used experimentally for blanching sweet corn (1). Basic patents covering the application of high-frequency dielectric heating to processing canned meat prod- ucts were obtained by Bowman (2) and Beadle and Bowman (3) of our laboratories. Satchell and Doty (4) reported the experimental application of the method for thawing frozen pork bellies. Although meat, and probably other food products as well, have a high dielectric constant and therefore should heat readily in a high- frequency dielectric field, the method of heating offers certain dif- ficulties because of the high conductivity and non-homogeneity of the product. However, with proper design of processing equipment it is possible to heat meat products to uniform processing temperatures in a very short time. The technique has an advantage over present steam- retort methods in that the product is heated uniformly, and over- cooking near the outside of the container is avoided. Equipment used. As a source of high-frequency energy we have used an indus- trial model 15 KW oscillator capable of operating at frequencies of 2-10 mega- cycles. All of our processing studies have been made at frequencies of approxi- mately 9 megacycles. Basically, the experimental design for processing equipment is illustrated in Figure 1. The dimensions of the processing cell are limited by the properties of 95

•LASS WALLED MEAT PRODUCT JYLINDER TO BE HEATFn ,\ J~ OSCILLATOR .V •'*•*•• vi^ -_-.£• 0 uuu TUNING COIL 'H fT/fifS' v I TUNING _._ CONDENSER METAL EN ~ PLATES D lFTf FIGURE 1. SCHEMATIC DIAGRAM OF EXPERIMENTAL EQUIPMENT USED FOR PROCESSING MEAT PRODUCTS. the product to be heated and the characteristics of the oscillator used. For our oscillator, which has an internal resistance of 80 ohms, we have been able to use cells 4 inches or 6 inches in diameter and 6 inches to 24 inches long. The longer length is desirable because the total resistance of the meat more nearly balances the internal resistance of the oscillator. Materials used. We have processed the following meat products in the equip- ment described: pork luncheon meat (cure in) ; fresh pork luncheon meat; boned cured hams; and ground beef at 12'/ and 25V< fat content. Temperature uniformity in products processed. If high-frequency heating is to be used for processing meat products for canning, the temperatures attained in a definite time must be uniform throughout the body of the meat. We have been able to attain reasonably uniform temperatures in pork luncheon meat along the entire axis of the meat cylinder (Table 1). The temperatures at right angles to the axis of the meat cylinder were also quite uniform except for areas immediately adjacent to the wall of the processor (Figure 2). If the heat lost to too- 180- K>0- 80- WALL e s 4 DISTANCE FROM WALL dock dlxl.lon.l'J WALL FIGURE 2. TEMPERATURE DISTRIBUTION ALONG THE DIAMETER OF A CYLINDER OK PORK LUNCHEON MEAT. SHADED AREAS INDICATE HEAT LOST TO PROCESSING CELL WALLS. 96

TABLE 1 TEMPERATURE DISTRIBUTION ALONG THE Axis OF PORK LUNCHEON MEAT CYLINDER (9 KV; 1.5 amperes at 10 megacycles) wt 2" 6" 10" 14" 18" 22" Run of of Avg. No. Meat Heating Temp. (Ibs.) (min.) Distance from End of Processor Temperature — °F. op 4 10.25 3.20 172 196 185 185 206 196 188 5 13.00 5.33 226 241 235 255 249 242 6 13.00 4.83 250 255 256 241 254 260 251 the walls of the processing cell is taken into account (see shaded areas, Figure 2), the variations in temperature throughout the body of the meat cylinder were not great. The temperature distribution in boned hams heated by this process has not been quite so satisfactory (Table 2). As for luncheon meat, the lowest tempera- tures were near the walls of the processing cell, and refined experimental tech- niques and improvements in the processing cell should lead to more uniform heating. Sterility of products processed. To determine whether or not meat products could be effectively processed from a sterility standpoint, pork luncheon meat, ground fresh pork, and ground beef were inoculated with spores of the culture of putrefactive anaerobe designated as P.A. 3679, and processed at different times and temperatures. The inoculated sample for bacteriological study was packed in a small "wiener" enclosed in a cellulose casing which was placed in the center of the processor full of meat. After heating and cooling, the inoculated wiener was emulsified in a mechanical blender and then subcultured in a pea broth at 30° C. For some of the heating trials the wiener was placed in a sterile tube and incubated without subculturing. If growth occurred, further bacteriological examination was made to establish definitely that it was actually P.A. 3679 and not other organisms that may have entered as contaminants after processing. The sterilization efficiency for each separate processing run was determined by cal- culating the Fu—value (z=18) using the graphical method described by Shultz and Olson (S). The results (Table 3) show that these heat-resistant spores were killed at F0—values comparable to those reported for conventional steam sterilization. For pork luncheon meat (cure in), processing to F0—values of about 1.0 or less appears to yield a product in which P.A. 3679 spores will not grow out unless subcultured. For uncured pork and ground beef the need for processing to F0—values near 7.0 is indicated for the spore load employed. TABLE 2 THE TEMPERATURE OF 11-PouND BONED HAMS PROCESSED IN A CELL 6 INCHES IN DIAMETER AND 12 INCHES LONG Heating time (min.) (9 KV; 10 megacycles) Temperature °F. Current (amperes) Mean Max. Min. Avg. Dev. 1.3 1.3 7.52 7.35 4.55 224 222 232 246 254 258 150 166 161 16 21 1.8 19 97

TABLE 3 EFFECTIVENESS OF HIGH FREQUENCY STERILIZATION OF COMMINUTED MEAT INOCULATED WITH P.A. 3679 SPORES (100 spores per gram in a 25-gram sample) Temp. Range at Max. (°F.) Time in Max. range (min.) Type of Meat Cooling Time (min.) Approx. F,, Value P.A. 3679 Growth Luncheon Meat 248-252 2.5 3.5 4.7 Luncheon Meat 250-252 0.25 3.5 2.1 + Luncheon Meat a .. 228-237 6.5 11.0 0.8 Fresh Pork .. 246-255 4.5 4.5 7.8 Fresh Pork " 246-254 3.5 5.5 5.9 + Fresh Pork a .... 238-246 2.5 4.5 2.0 + Ground Beef a (25% fat) 248-256 4.5 3.5 7.0 Ground Beef " (25% fat) ...... 250-255 2.0 3.0 2.6 + " Meat incubated without subculturing. Palatability characteristics. Boned ham heated by high frequency to an F0—value of 2.76 scored 7.85 (very good) by an acceptance panel which scored ham chunks from a regular Army canned ration item 6.90 at the same time. In a critical taste panel evaluation of pork luncheon meat in a regular 6-pound Army pack as compared to dielectrically-processed luncheon meat from the same mix, 6 panel members out of 10 preferred the high-frequency processed sample. The dielectrically-heated sample was of firmer texture with no overcooked flavor, but was not as juicy as the product processed by conventional steam heating. In a consumer-type preference test involving 44 representatives of the meat- canning industry, 32 (73%) preferred the dielectrically-processed meat (served cold) over the regularly steam-processed meat. An acceptance panel consisting of 81 testers at the QM Food and Container Institute laboratories expressed a significant preference for the dielectrically-processed luncheon meat over meat processed by standard methods when the meat was served cold. When the meat was served hot, the preference was not as pronounced. These preliminary taste panel evaluation studies indicate that ham and pork luncheon meat heated by high frequency is somewhat superior in texture and flavor to comparable meat heat processed by conventional methods. As yet we have no information on the stability of dielectrically-processed meats. Practical evaluation and application of high frequency heating for canned meat products The results reported indicate that high-frequency heating can be applied for the processing of canned meat products if only the quality of the processed meat and sterilization effectiveness are considered. From a practical and technological standpoint, however, there are some very important problems to be solved. Efficiency calculations with several processing runs with our ex- perimental equipment indicate that 55r/(-58% of the electrical energy input to the oscillator is recovered as heat in the meat and processing cell. With this efficiency the actual heat cost for processing meat would be approximately 0.3 cents per pound with present electrical rates in the Chicago area. Amortization and maintenance costs on the high- frequency oscillator would probably cost approximately the same 98

amount. Thus, the total heating cost for processing would amount to less than one cent per pound of meat. While comparable figures are not readily available for processing by the present steam-retort method it is likely that the actual total heating cost, including maintenance and amortization of equipment, is 0.2 to 0.3 cents per pound. Thus, the comparative cost of high-frequency heating is not excessive if a superior, high-quality product is obtained. There are 2 important drawbacks to the technological adoption of the high-frequency heating of meat products for canning. First, the initial equipment cost is high and the capacity is limited. With a 15 KW oscillator costing approximately $10,000 it would be possible to heat process only about 200 pounds of meat per hour. Secondly, it would be necessary to use a continuous processor followed by aseptic packing in sterile containers, or to use a container with metal ends and insulating walls for processing. Although we are attempting to develop materials and techniques that may overcome this 2nd dis- advantage, the solution of the problem is not yet in sight. Summary Pork luncheon meat and boned hams may be heat processed by means of high-frequency, dielectric-type heating. The heated product has usually been judged to be of as good or better quality than com- parable meat processed by the conventional steam-heating method. The meat can be effectively sterilized without developing the typical overcooked flavor and odor exhibited by most meat items sterilized by the methods now in commercial use. The heating costs for the high-frequency process probably would be somewhat higher than those for steam processing but would be fully justified if a product of superior quality could be consistently obtained. The high original cost for equipment, the limited capacity of the equipment, and the development of a suitable continuous processor or processing containers are disadvantages of the process that must be considered before technological application of the processing method can be recommended. Literature Cited 1. Anonymous. Food Eng., 23, (5), 81 (1951). 2. Bowman, J. U. S. Patent 2,488,164 (Nov. 15, 1949). 3. Bowman, J., and Beadle, B. W. U. S. Patent 2,488,165 (Nov. 15, 1949). 4. Satchell, F. E., and Doty, D. M. American Meat Institute Founda- tion Bulletin No. 12 (1951). 5. Shultz, 0. T., and Olson, F. C. W. Food Research, 5, 399 (1940). CHAIRMAN WIESMAN Thank you very much, Dr. Doty. There are certainly many inter- esting implications in connection with the possibility of using dielec- tric heating. I am sure there will be a lot of questions on this subject this afternoon. 99

WEDNESDAY AFTERNOON SESSION April 1, 1953 CHAIRMAN WIESMAN The next paper will be presented by Mr. Joseph Stukis of the Quartermaster Food and Container Institute. Technological information Obtained from Storage Studies on Canned Whole Hams Processed by Intermittent Heat Treatment J. M. STUKIS In recent years, several avenues of approach have been contem- plated in the attempt to secure a mild-flavored ham. One approach has been based upon the lard-packing of properly cured and smoked hams. A second method has been the use of intermittent heat treatment as applied to canned whole boneless hams. More recent developments in- clude the application of dielectrics to the sterilization of whole hams. Work currently under way concerns the application of electron bomb- ardment and the use of nuclear fission byproducts as a means of securing a sterile product. This discussion will be concerned with the second method, intermittent heat treatment. A canned meat product, intended for Armed Forces use, must possess a minimum stability equal to 6 months at 100°F. or 2 years at 72° F. These standards are predicted on needs established by the extended supply channels—virtually world-wide in scope—now being used by our Armed Forces. . The canned ham product, as seen and consumed by the service- man, must be equal in acceptance to the product with which the con- sumer is familiar. That is to say, the color, odor, flavor, and texture must be closely similar to those of a canned perishable ham of com- merce. The yield of edible meat per can must be high and the product easy to slice and prepare for serving. Late in 1951, a member of the Research and Development As- sociates, Food and Container Institute, Inc., aware of the need for a sterile whole ham, offered his assistance in solving the problem. The process suggested was that described in U. S. Patent 2,305,480, dated December 15, 1952, entitled "Production of Canned Meats for Stor- age." Purpose of the procedures specified in the patent was: "to sub- ject canned meat to a temperature which assures incubation of thermo- philic and hence other bacteria and then to heat the canned meat under conditions to assure killing the thermophilic and other bacteria . . . ," "to effect, in process, a flavoring development of amino acids," and "to effect sterilization by steam generated within the can, of the can walls and ham surfaces." 100

The following sentences extracted from the above-mentioned patent best describe the reasoning employed: "By the present inven- tion, conditions are imposed which will assure that dormant life awaken and enter the active phase, whereby it can then be killed by lower temperatures while the meat is cooking under conditions to limit purging. One essential of this treatment is to avoid too long an exposure for awakening the dormant life, so that spoilage in the can is not effected." The patent described intermittent heat treatment" as applied to raw meat, incompletely cooked meat, and cooked meat when canned. Details of the patent as applied to raw cured ham are quite similar to those described in this paper. Experimental Procedures In December of 1951, production of 182 hams by the method described in the patent, "Production of Canned Meats for Storage," was completed. Production of the hams took place in a plant maintained under the regulations of the U. S. Department of Agriculture, Bureau of Animal Industry, Meat Inspection Division. The production of the hams was observed by food technologists from the QMFCI and the patent holders. Forty-five of the hams so produced were utilized by the QMFCI for test purposes. The production of the test hams began with the selection of the raw material. The hams utilized were in the 15-pound weight range, plus or minus one pound. The hams, 2 days old when production was initiated, were of good conformation, light in color, and of smooth-textured flesh. The hams were obtained from hogs of various breeds and were said to be from midwestern and southern farms. The skinning of the hams was followed by the curing operation. An artery pump was used, with a weight increase of 10r/r. The pumping pickle used was prepared according to the following formula: 50 gallons of water, 120 pounds of salt, and 13% pounds of a commercial curing agent composed of sodium chloride, sodium nitrite, sodium nitrate, and dextrose. The temperature of the ham at the time of pumping was 30°-36° F., and the temperature of the pickle, was 36°-40° F. After a short draining period, the pumped hams were rubbed with 3 pounds of the following mixture for each 100 pounds of ham: 25 pounds of salt and 5 pounds of the commercial curing mixture described above. The rubbed hams were then placed in the curing cellar on racks in 3 layers starting at floor level. The curing cellar was maintained at a temperature of 38°-40° F. The dry-cure period was 6 days long. "It should be pointed out that sterilization through intermittent heat treat- ment is known by such names as fractional sterilization, intermittent sterilization, or Tyndallization. The process dates back to 1877, when the English physicist, Tyndall, discovered that one hour of exposure to boiling temperature might not kill every microbe in a nutrient infusion, but that boiling for one minute on 5 successive occasions with intervals of several hours at room temperature would succeed in sterilizing. Based on those experiments, Tyndall concluded that bacteria exist in 2 forms, one thermolabile and one thermostable. In our day, the process is commonly employed to reduce the likelihood of chemical breakdown during sterilization of certain bacteriological media which would decompose more rapidly at higher temperatures and prolonged processing times. 101

After the hams were cured, they were scrubbed and washed under showers, skinning was completed, and the product defatted to the proper level. Boning was accomplished in the usual commercial manner. At the time of boning, it was found that the hams had gained 6r/t in weight over their original weight (that is, the weight of the boneless cured ham at the time of canning, plus the weight of the skin, bones, fat, and trimmings did not exceed 106 r/r of the weight of the fresh uncured ham). No smoking was employed in this process. It should be noted that all of the equipment with which the ham came into contact during the above described curing and boning procedure had been thoroughly cleaned prior to use with a commercial cleaning compound, dissolved in a specified amount of water, and used as a liquid cleaner. Active ingredients were sodium carbonate, trisodium phosphate, a quaternary ammonium salt, and a sodium alkyl aryl sulphonate. After boning, the hams were moved by means of a conveyor to a workman performing the weighing operation. At the weighing point, a chute delivered washed pear-shaped cans to the scaleman. The hams were placed into the cans and a workman marked them with the proper weight and a "T," designating "test product." At the end of the conveyor line the ham was removed from the can, the shank end tucked into the bone cavity and returned to the can with the fat side up and the shank end toward the smaller dimension of the pear-shaped can. The hams were then conveyed to a meat press, a hydraulic device with a pear- shaped compression foot. Pressure was applied and the product made to conform to the shape of the can. The compressed product was next moved to a crimping machine where a lid was crimped into place. The packaged product was next moved to the soldering pot and the crimped side of the can fluxed and dipped into molten solder. When the can was sealed (with the exception of the steam vent) it was ready for its first heat treatment. The cans, with the longest dimension in the vertical position, and with the steam vent on top, passed by means of a conveyor through an oil bath (lard maintained at 340° F.) for an exposure time of 8 minutes. The vent end, that is, the smaller end of the pear-shaped can, was approximately 3 to 4 inches out of the hot lard. As the cans passed through the hot lard, strong steam and air pressures were generated; these pressures were forcefully released through the steam vent. As the cans emerged from the hot lard bath and the steam and air pressures were subsiding, the vent was capped with solder. It was observed that in some instances pressures created during the hot bath were great enough to buckle the end plates of the can at the time of sealing. In severe cases, the hams were repacked. As the cans began to cool, sufficient vacuum was obtained to collapse or panel the can in several places along the body of the can and to draw in the can ends firmly. The cans of ham were then placed in a cooking tank (a retort) and were held at 127° F. (temperature of the water) (see Figure 1) for 4% hours, the temperature was then raised to 135° F. and held at this level for 2 hours, or until the internal temperature of the can at the center of the product reached 129° F. The cans were then transferred to the chilling room at 54° F. and kept there over- night. On the second day of processing, the canned hams were again placed in the cooking tank and given the following process: 2% hours at 127° F. (water temp.)—reaching an internal temperature of approximately 98° F. 2% hours at 180° F. (water temp.)—reaching an internal temperature of approximately 146° F. 102

HEAT PROCESSING SCHEDULE FOR CANNED HAM 130 110 iao ISO 140 ISO H no 2" _ 100 1st Day Cook W»ter °F. / f^-^^^~^^—l ** 1 2 3 4 5 8 7 1« 20 21 22 23 24 25 88 27 28 29 SO 31 32 HOURS FIGURE 1 PROCESSING SCHEDULE FOR CANNED WHOLE HAMS—INTERMITTENT HEAT TREATMENT 4% hours at 170° F. (water temp.)—reaching an internal temperature of approximately 165° F. 2 hours of cooling at approximately 42° F.—reaching an average internal temperature of 100° F. The product was then transferred to the chilling room for a 24-hour holding period at approximately 50° F.b While a representative number of canned hams were undergoing incubation, plans were being formulated as to the methods to be employed in testing the product. During this period, the National Research Council, Committee on Foods, Subcommittee on Animal Products, at the request of the QMFCI, solicited opinions on the procedures, as outlined in the covering patent, from 25 leading academic and industrial bacteriologists, with results as follows: None suggested the adoption of the procedure without further testing; one had no opinion; 10 recommended further testing; 4 recommended fur- b It is interesting to note that a 10-pound canned ham can be rendered sterile by conventional heat processing in approximately 6 hours at a temperature of 230° F. However, this severe treatment makes it unacceptable to the consumer, particularly with regard to texture and flavor. Canned perishable ham for com- mercial use receives a 170° F. hot-water cook for 4 to 6% hours, depending upon the size of the ham. More recent experiments, using dielectric treatment, have shown that a 10-pound ham can be sterilized to an F»—value of 10 in 8 minutes and 40 seconds. 103

Ham For Slice Test & Microbiological Exam. Sllceablllty Testing Area' Cut to reveal. Intersection of femur & pelvic girdle A, B, C, D - Sample Areas Marks off fOT Bacteriological examination - HOCK end FIGURE 2 CROSS SECTION OF HAM PRIOR TO BONING ther testing but were dubious as to the success of such a test; and 10 stated that the process was without merit and recommended that further testing not be considered. However, it was decided that further tests should be conducted in order that the merits of the process be completely appraised. It was decided that in addition to initial examinations, the canned hams would be subjected to storage for periods up to one year at temperatures of 40° F. (the control), 72° F., and 100° F. Three hams were to be withdrawn from each of the 3 temperatures at the end of approximately every 3 months, bringing the total to 9 hams per evaluation period. Therefore, 5 evaluation periods were estab- lished, initial, 3, 6, 10, and 12 months. It was further decided that bacteriological, chemical, and technological tests would be conducted. Consumer acceptance tests were excluded from the plan since doubt was expressed among those whose opinions were surveyed as to the soundness of the process from the public health standpoint. At the beginning of the bacteriological examinations, vacuum readings were made on each can after sterilizing the surface of the narrow end of the can and the tip of the gauge. After taking the vacuum reading, the gas in the head space was collected in a gas analyzer apparatus. Each can was then opened under aseptic conditions and the ham transferred to a sterile tray. Sampling procedures were performed in a sterile room equipped with an ultraviolet sterilizing lamp and posi- tive air pressure. Samples were taken from areas A, B, C, and D (see Figure 2) 104

as well as from the juice and gelatin liquid surrounding the ham. Area B was in the center of the ham at the hock end where the bone joint had been removed, and area D was in the center section at the butt end from where the acetabulum had been removed. It was felt that the cavities left in these areas by removal of the ham bones might afford particularly favorable conditions for the survival of organisms during processing. Areas A and C were cross sections through the thick muscle portions of the hams. Approximately 100 g. of meat were taken from each area, using sterile stainless steel borers and boning knives. Each weighed sample removed for bacteriological culturing was blended for 10 minutes in a Waring blender with distilled water to make a 1:5 dilution of meat (or juice). Fifty ml. volumetric pipettes with enlarged tips were used to transfer 50 ml. amounts of this 1:5 dilution (10 g.) to bottles and flasks of media. The importance of using large enough meat samples has been emphasized by the work done on the incidence of anaerobic spores in meat. Harriman et al. reported (2) an average load of 2-4 anaerobic spores per g. in fresh and cured pork trimmings, while Burke et al. (1) found an incidence of less than one spore per g. in fresh, cured, and processed pork trimmings. One ml. amounts of this 1:5 dilution, as well as higher dilutions, were transferred to Petri plates and mixed with TGE agar medium for standard plate counts and isolation of aerobic organisms. The TGE agar plates were incubated at 32° C. for 48 hours in order to make standard plate counts of aerobic organisms. Also, direct smears were made of this 1:5 sample dilution and examined micro- scopically. All materials and equipment used in the preparation and inoculation of samples were sterile. The 50 ml. amounts containing 10 g. of meat or juice were separately inoculated into capped bottles containing 150 ml. of beef-heart infusion or thioglycollate broth, and into cotton-stoppered flasks containing 150 ml. of TGE broth. The formulae of the media used were varied to some extent during the course of this study in an attempt to establish the optimal growth conditions for isolation of the ham flora. After inoculation, the anaerobic cultures in tubes and bottles were sealed with paraffin and heated at 80° C. for 10 minutes, making the come-up and come-down times as brief as possible. All aerobic and anaerobic broth cultures were divided into 2 sets for incubation at both 32° C. and 55" C. After 2 weeks incubation, the cultures were examined microscopically and for such visual changes as gas evolution, darkening of meat, or digestion of meat. Subcultures were made where necessary for identifying types of organisms. All cultures were held for 30 days and examined again at the end of this period before being reported as negative. Chemical analyses included determinations for moisture, ash, fat, protein, chlorides as NaCl, sodium nitrite, and sodium nitrate, reducing sugars and total sugars as dextrose. The peroxide value and free fatty acid development were measured. The pH of all samples was determined. An attempt was made to measure protein degradation through the measurement of free ammonia, water- soluble amino nitrogen, total reducing capacity, non-protein reducing capacity, total salt-soluble nitrogen, total salt-soluble non-protein nitrogen, and total salt- soluble protein nitrogen. Ham juices were analyzed for free ammonia, water- soluble amino nitrogen, sodium nitrate, sodium nitrite, and pH. The density of the juice was also calculated. Gas analysis was made on the head-space gas of all hams. Technological examination of the samples included an evaluation of the color, odor, sliceability, and yield on a drained weight basis. The sliceability test, de- veloped by the QMFCI to determine the ease with which a product slices, was used 105

as a measurement of the firmness of the product. The slicing is performed in an area just to the rear of the butt section (see Figure 2). The ability to obtain a well-defined slice, which is the mirror image of the mass from which it was ob- tained, is directly related to the texture of the product. The thinner the cut at which a well-defined slice can be obtained, the better quality texture a product possesses. A Hobart electric slicing machine, which is equipped with a %-hp motor delivering a speed of 1750 r.p.m., was used for slicing. The cutting blade had a diameter of 10% inches, % of an inch of which comes into contact with the product. Numerical values on sliceability were obtained by a direct reading of the control knob. Correlations were sought between chemical changes as Re- flected by analysis, and physical changes as reflected by gross technological examinations and sliceability. Results and Discussion The findings of the 12-month storage study were reviewed and conclusions drawn with the minimum military stability standard of 6 months at 100 °F. and the desired stability standard of 12 months at 100°F. kept well in mind. Vacuum data are inconclusive, except it might be noted that this process produced a maximum vacuum of 5 inches in this test. Bac- teriological examination showed both aerobic vegetative types and anaerobic spore-forming organisms in the canned hams at the begin- ning of storage. Thus, it was concluded that the product was not sterilized by the intermittent heat process used. In addition, one ham which showed evidence of swelling after 2 weeks incubation at 72°F., was examined bacteriologically and showed the presence of small numbers of gram-positive sporulating bacilli, mainly aerobic and mesophilic. These organisms were also found in the 3 hams ex- amined initially. In addition, -gram-positive staphylococci were iso- lated from section D (intersection of the femur and the pelvic girdle) and the juice. Storage at 72° and 100°F. showed that bacteria not only survive for months but actually multiply in these hams and build up sizable bacterial populations. Aerobic counts in these hams rose sharply during the early part of the storage and then began dropping off. At 100°F. storage, the plate counts had fallen from 15,000 g. at 3 months to 500 at 10 months, while at 72°F. storage, the plate counts dropped from 700 to less than 10 over the same period. Although quantitative counts were not made of the sporulating anaerobes, their presence was noted in all hams examined during this study, except in the 100°F. hams stored for 10 months. This may be interpreted as practically complete germination of spores within 10 months at the elevated temperature and, consequently, a dangerous situation if Clostridium botulinum were present, and a putrefactive condition if putrefactive anaerobes were present. In most cases, smears made of the 1:5 dilution of meat or juice samples did not reveal the definite presence of organisms. Direct microscopic examination of products such as canned ham is not a reliable indication of the bacterial load. 106

No definite correlation could be drawn between the incidence of organ- isms and the particular section of ham examined. There was some indication that the juice contained less bacteria than the tissue sec- tions. Evaluation of the data obtained from chemical analyses0, which included proximate analysis, free ammonia, water-soluble amino nitrogen, reducing sugars, total reducing capacity, non-protein reduc- ing capacity, salt-soluble nitrogen, salt-soluble, non-protein nitrogen, salt-soluble protein, peroxide value, free fatty acid, and pH, leads to the conclusion that the chemical changes, as measured in this study, were slight in nature. It was believed that certain chemical changes took place which resulted in a product of reduced acceptability, how- ever, these changes were not measurable by the methods of analyses used. It was further concluded that the extent and nature of the chemical changes were in keeping with the temperatures and lengths of storage. It should be noted, however, that the peroxide value and free fatty acid content showed a significant increase. Analyses of head-space gases showed the presence of C02 in a range from 14.9% to 43.4 %. It was concluded that these values were in keeping with the findings of the microbiological examinations except for samples stored at 40 °F. where C02 in quantities as high as 25 % was found with no apparent microbiological changes. With the exception of 2 cans, it was found that from 20% to 33% of the product was cooked-out juices. From this it was concluded that the yields, with regard to range, did not vary greatly regardless of the time or temperature of the storage. It was further concluded that by comparison to the requirements of the current Federal speci- fication for canned whole ham (limitation of 121/27° gelatinous material in the can) the yields found in this study are considered to be low. With regard to product color, it was concluded that the color was satisfactory for 12 months at 40°F., 6 months at 72°F., and 3 months at 100°F. It was concluded that the odor of the product re- mained satisfactory for 12 months at 40°F., until 10 months at 72°F., and until the 6th month at 100°F., whereupon it became unsatisfac- tory. The texture as determined by the sliceability test was satisfac- tory until the 10th month at 40°F., with some evidence of deteriora- tion of texture after the 10-month level. The texture was unsatis- factory afer 10 months at 72°F., and 3 months at 100°F. The flavor of the product was found to be satisfactory upon initial examination, but the product was not tasted afterwards because of potential micro- biological hazards. '' Detailed results of all aspects of the technological, bacteriological, and chemical tests reported herein are available upon request to the Quartermaster Food and Container Institute for the Armed Forces, 1819 W. Pershing Road, Chicago 9, Illinois. 107

Examination of the cans after storage indicated that tin plate deterioration commenced after 6 months at 100 °F. and progressed noticeably through the 12th month at 100°F. Analysis of head-space gases showed hydrogen to be present in amounts as high as 16.7% after storage at 100°F. for 10 months. It was concluded that the high percentage of hydrogen present in the head-space gas was chiefly the result of the reaction between the product and the container. Through the course of study it was noted that there occurred a progressive loss of can paneling. On the basis of the findings reported above, it has been deter- mined that the application of intermittent heat treatment to whole canned hams is not at this time a satisfactory solution to the quest of the Armed Forces for a stable whole ham that will keep without refrigeration. Literature Cited 1. Burke, M. V., et al. Methods for determining the incidence of putre- factive anaerobic spores in meat products. Food Technol., 4, 21- 25 (1950). 2. Harriman, L. A., et al. Spore formers in pork. Annual Meeting, 111. Soc. Amer. Bacteriologists (1948). CHAIRMAN WIESMAN Thank you very much, Mr. Stukis. Up until now we have talked about processing canned meats using some form of heat or another. We heard papers describing the normal type of heat processing. We have heard about strata cook. We have heard about the continuous cooking, using aseptic filling. This morning we heard about the pressurized system for heat treat- ment, intermittent heat, and now we are going to have a couple of papers which are going to consider the processing of canned meat items using what might be termed cold sterilization. The first of these papers is by Dr. L. E. Brownell, who is head of the Fission Products Laboratory at the University of Michigan. Potentialities of Utilising Radiation from Fission Materials for the Production of Canned Meat Products L. E. BROWNELL Research by a number of investigators has shown that a variety of types of ionizing radiation can be used to destroy microorganisms. This has led to consideration of using ionizing radiation to sterilize food and thereby prevent food spoilage resulting from the action of microorganisms. One such application would be the substitution of radiation sterilization for thermal sterilization in the processing of canned meats and other foods. An advantage of the use of radiation 108

in the processing of canned foods is the elimination of the require- ment of processing at elevated temperatures. Another advantage lies in the instant penetration of radiation as compared to the slow pene- tration of heat. However, the use of radiation has numerous disad- vantages and presents some new problems. The early studies were made with X-radiation (5). X-rays have never been considered seriously as a means of sterilizing foods be- cause of the high cost of using X-ray machines for this purpose. Electron accelerating machines, such as the Van de Graff machine and the Capacitron, have been developed and improved during the past several years, and their use in sterilizing foods and other prod- ucts has been demonstrated (1, 5). Current interest has developed in the use of gamma radiation as a means of sterilizing foods because of the possible availability of large amounts of radioactive wastes produced as byproducts in the operation of nuclear reactors. Gamma radiation has the advantage of appreciably greater penetration than either electrons from accelerating machines or X-rays from conven- tional 200 KV machines. Gamma radiation obtained from radioactive wastes could be much cheaper than X-radiation from machines; how- ever, as yet only limited cost information on these wastes is available. The Atomic Energy Commission has contracted with the Engi- neering Research Institute of the University of Michigan and other universities to investigate the possible industrial uses of radioactive wastes. The Michigan Memorial Phoenix Project8 supports research on the uses of atomic energy which will benefit mankind. This proj- ect is separate from the contracted research conducted by the Engi- neering Research Institute and has no connection with the Atomic Energy Commission. Both of these projects at the University of Michigan have conducted experiments on the uses of gamma radia- tion. This research was begun in the summer of 1951 when the Fission Products Laboratory of the Engineering Research Institute received a one-kilocurie cobalt-60 source of the type described by Manowitz U). Sterilization by gamma radiation. One of the first of the questions investi- gated was the dosage required to destroy various microorganisms. The Michigan Memorial Phoenix Projects 20 and 41 have supported a study of the effects of a The Michigan Memorial Phoenix Project is a memorial to the Michigan dead of World War II. The Regents of the University at their meeting on May 1, 1948, on recommendation of their War Memorial Committee, voted to "create a War Memorial Center to explore the ways and means by which the potentialities of atomic energy may become a beneficent influence in the life of man, to be known as the Phoenix Project of the University of Michigan." In taking this action the Regents recognized that the release of the energy of the atom through fission is destined to alter almost all aspects of our civilization and culture for many years to come and stated their intention to establish a center to support re- searches and studies on all phases of the impact of nuclear energy on our life. 109

gamma radiation on microorganisms. A wide variety of bacteria, molds, yeasts, and viruses were tested and spore-forming bacteria were found to be the most resistant organism tested. Bacillus subtilis and Clostridium botulinum require a dose of approximately 2.0 to 2.5 million rep (measured in air) to destroy all the spores and bring about complete sterility. Table 1 gives typical data obtained with Bacillus subtilis. TABLE 1 EFFECT OF DOSAGE OF GAMMA RADIATION ON COUNT OF Bacillus Subtilis Radiation Dose, Million Rep (in air) Count of Bacillus subtilis Per Cent Reduction 0 0.34 0.68 1.02 1.35 1.70 2.04 18,000,000 960,000 202,000 20,500 14,450 75 0 0 94.6+ 98.8+ 99.9+ 99.9+ 99.9+ 100.0 Much smaller dosages were required to destroy the non-spore-forming types of bacteria. For example, a dose only about I/6th as large was sufficient to de- stroy the microorganisms Eschericha coli, Proteus vulgaris, and Lactobacillus arabinosus. A similar small dose (less than 400,000 rep in air) destroyed the yeast Saccharomyces cerevisiae, and the molds Penicillium notatum and Asper- gillus niger. Tests were also made on the flora of raw and pasteurized milk. A dose of 2.04 million rep (in air) gave a count of zero in both raw and pasteurized milk. A gram-positive sporulating bacillus isolated from canned evaporated milk was found to have about the same resistance as Bacillus subtilis. A dose of 2.04 million rep (in air) gave a count of zero. It might be added that 2 pathogenic viruses, psittacosis virus and mouse pneumonitis, have been treated with gamma radiation. Both viruses were in- activated and rendered noninfective by relatively small dosages of greater than 0.085 and less than 0.26 million rep (in air). These experiments yielded the in- teresting finding that these pathogens are much more susceptible to radiation than sporulating bacteria. Animal feeding experiments. A few months after receiving the one-kilocurie gamma source some preliminary animal feeding experiments (2) with food ex- posed to gamma radiation were conducted by F. H. Bethell, M. D. The results showed no difference in health, growth, etc., between the animals fed irradiated whole milk and those fed the controls. All milk samples were irradiated in poly- ethylene bags in the one-kilocurie cobalt-60 source, receiving a dose of slightly over 2,000,000 rep (in air). The milk was reconstituted Klim prepared as a 4-times concentrate and diluted just before feeding by the addition of a salt solution. This milk constituted the entire diet with the exception of one leaf of lettuce added each week which was not irradiated. It was emphasized that this experiment was only exploratory and that any conclusions from the data were preliminary and contingent upon further testing, both with feeding experiments and more refined methods of assay for individual components of the diet. This 110

would require microbiological assay for amino acids and the setting up of long- term feeding and breeding experiments.15 In the experiment proposed, the main calorific intake should consist of a suitable mixture of carbohydrates, fats and proteins. In addition a portion of the water intake should be in the irradiated food. Some of the effects of irradia- tion are believed to result from the formation of hydrogen peroxide from water; therefore, it is important that the food to be irradiated not be in the anhydrous state. Also, the suggestion has been made that meat would be a more suitable and convenient food than reconstituted milk because of the difficulties of obtain- ing normal feeding with a complete liquid diet. The feeding experiment to establish the wholesomeness of irradiated food should be independent and not combined with an experiment which might involve the dosage of radiation required for sterility. If the animals are given food in which the wholesomeness of the food is independent of the requirements of sterili- zation by radiation, using food such as canned milk or canned meat which is sterilized thermally, the variable of radiation dosage required to sterilize the foods will not influence the experiment. This precaution will prevent the possible loss of animals from food spoilage which would destroy the experiment to investi- gate the wholesomeness of irradiated food. Experiments to further investigate the dose of gamma radiation necessary to produce sterility in canned foods may be conducted simultaneously and separately and at less cost by suitable micro- biological studies rather than by animal feeding experiments. With these different considerations it was decided that the animal feeding experiment should involve the feeding of 4 generations of rats. A diet should consist of irradiated food supplemented with vitamins and minerals. The irradi- ated food may consist of 50 parts of canned meat such as Swift's Chopped Beef for Babies, 25 parts of carbohydrates such as cornstarch, 10 parts of fat, 10 parts of dry casein and the remaining 5 parts be used to provide a supplement of mineral and non-irradiated vitamins. This diet has been suggested because it is believed that it will be necessary to supplement the ground meat with carbohy- drates, fat, inorganic salts, vitamins, and probably proteins for a completely satisfactory diet. Tests with irradiated foods. In the Fission Products Laboratory food has been packaged in plastic containers and in glass tubes and preserved from spoil- age by microorganisms for many months. Green vegetables such as peas, spinach, asparagus, broccoli, carrots, etc., seem to be most satisfactory foods for preserva- tion by irradiation. In the studies made in the Fission Products Laboratory it was found that these foods undergo very little flavor change; in fact, the peas and carrots seem to be slightly sweeter and are definitely more tender as a result of irradiation. There is a tendency to bleach, which is a disadvantage in the case of green peas but may not be a disadvantage in the case of asparagus and carrots. There also seems to be a softening of the foods with a certain amount of cell destruction, as evidenced by an increase in tenderness, a decrease in crispness, and the loss of some fluid from the cell. For example, irradiated peas cooked for 3 minutes have the same tenderness as the control cooked for 6 minutes. b The proposed long-term animal feeding experiments have been discussed with the personnel of other laboratories that have conducted similar experiments using food sterilized by electronic bombardment from accelerating machines. There has been some discussion of the proposed experiments in correspondence with representatives of the Food and Drug Administration. Ill

Flavor tests made in the Fission Products Laboratory indicated that protein foods of animal origin are not as satisfactory as fresh vegetables when treated by irradiation. In general, protein foods of animal origin undergo 2 types of flavor change; the proteins develop a strong animal-like odor and taste and the fats develop a tallowy or rancid odor and taste. These off-odors and off-flavors are quite volatile and in many instances disappear upon cooking. However, there seems to be little promise at present of irradiating foods such as milk, cottage cheese, and eggs without developing off-flavors that would be objectionable to a large percentage of the public, although some individuals are unable to detect these off-flavors except when very great doses of radiation have been used. Rats fed irradiated milk accept it as readily as the control. It was discovered that irradiated bacon, ham, and corned beef were relatively free of any off-flavors after these products were irradiated and then cooked. Representatives of a major packing company tasted samples of our irradiated bacon, corned beef, and ham and stated that the bacon had flavor which would be quite acceptable and that the corned beef was very good. The ham which was tested seemed to have a slight off-flavor of irradiation. However, other hams have been tested which were found to have no off-flavors after irradiation and cooking. It was believed that sodium nitrite and nitrate used in processing these meats protected the flavor molecules during irradiation. Other tests have been made using sodium nitrite with raw ground beef, and a noticeable improvement in flavor was observed. Concentrations of sodium nitrite as low as 100 parts per million appear to be effective in preventing flavor change. The Food and Drug Administration permits up to 200 p.p.m. of sodium nitrite in meats cured using sodium nitrite and/or sodium nitrate. One hundred parts per million of sodium nitrite does not affect the flavor of raw meat when cooked but does have a ten- dency to give cooked meat a reddish color rather than a greyish color. 10-kilocurie gamma, source. The original one-kilocurie source received by the Fission Products Laboratory has been useful in exploratory studies but has limited use because of the small size of the opening. No commercial size tin can would fit into this source and all experiments with irradiated food were conducted with glass test tubes or plastic bags as containers. Therefore, to provide better facilities for the irradiation experiments a new source consisting of 10-kilocuries of cobalt-60 in the form of 100 cobalt rods %-inch in diameter by 10 inches long with aluminum jackets has been irradiated in the NRX reactor at Chalk River, Canada, selected because of its high flux and the availability of radiation time at this installation. This new 10-kilocurie source is housed in a radiation room with 4 feet of concrete shielding in all walls. The source is "shut off" by lowering it into a pit of water 16 feet deep located in the center of the radiation room. The radiation room has a floor area of 8 feet by 11 feet and a height of 8 feet, which permits ample space for setting up a variety of experiments which may be run simul- taneously. The point of highest flux will receive a radiation dose of about 200,000 rep/hr in air throughout a cylindrical volume of 6 inches in diameter and 10 inches long. A flux of about half this intensity will be available immediately outside the double ring of cobalt rods. At further distances the flux will be decreased by the inverse square law and by absorption of radiation by the experimental samples and equipment. The Fission Products Laboratory now is one of the best equipped laboratories to handle gamma irradiation experiments as a result of its radiation chamber and 112

the one- and 10-kilocurie sources of gamma radiation. With the new source it is possible to irradiate a No. 10 size tin container, whole hams and sufficient volumes of food to conduct appropriate animal feeding experiments. It has been estimated that the new 10-kilocurie cobalt-60 source in the Fission Products Laboratory has increased the irradiation facilities at this laboratory perhaps more than 30-fold. The research performed at the University of Michigan on the u^es of gamma radiation is at present limited by the number of research personnel employed. In the field of the irradiation of food, the Michigan Memorial Phoenix Project will support the animal feeding experiment in which 4 or more generations of animals will be given food treated with a sterilizing dose of gamma radiation. The studies of the effect of gamma radiation on trichina in pork and pork products will also be continued by the Phoenix Project. At present, the Engineering Re- search Institute has limited its studies with gamma radiation to the investigation of chemical reactions promoted by gamma rays. New research projects will be brought into the laboratory in an attempt to attain maximum use of the radia- tion facilities. The chemical industry and the oil industry has shown more interest in making use of these facilities than has the food industry. The authors have some concern over possible loss by default of what is considered to be the most powerful and versatile gamma source for the studying of irradiation of foods. Sterilizing canned meat. At the writing of this manuscript no meat canned in tin containers has been irradiated in the Fission Prod- ucts Laboratory. A western model can-closing machine has been sup- plied to the laboratory by the American Can Company and has been put into operating condition. A variety of foods will be canned and irradiated this spring. However, with present support, these tests will be rather limited. The possible future of the process of gamma ray sterilization of canned meat is very promising in spite of the hurdles yet to be crossed. The penetration of gamma radiation gives it a great advantage over other types of radiation. For example, if a radiation dose of 2,000,000 rep is required for sterilization, the average radiation by electron bombardment may be 4,000,000 rep (8,000,000 or more near the sur- face and the minimum of 2,000,000 in the center) as compared to an almost uniform 2,000,000 rep with gamma radiation. Where irradia- tion results in flavor change, this difference in uniformity of dosage is an important consideration. Of course, there are disadvantages of using gamma radiation such as the longer time required to sterilize with gamma rays, the inability to stop gamma radiation except by shielding, and the present unavailability of cheap gamma sources. However, at present gamma radiation appears to be the only type of ionizing radiation which may prove to be feasible for sterilizing large size containers (No. 10 or 12) of canned foods. Summary Three important steps must be taken before food can be preserved by gamma radiation on a commercial basis: (1) food sterilized by gamma radiation must be proved acceptable to the Food and Drug Administration's requirements and to consumers' tastes; (2) industry 113

must show an interest by supporting research work to develop the process in terms of commercial feasibility; and (3) the Atomic Energy Commission must make suitable fission product gamma-ray sources available in sufficient quantities and at reasonable costs. Literature Cited 1. Brash, A., and Huber, W. Ultrashort application time of pene- trating electrons: a tool for the sterilization and preservation of food in the raw state. Science, 105, 112 (1947). 2. Brownell, L. E., et al. Utilization of gross fission products. Prog- ress Report 2 (COO-90-Project M943) 60, Engineering Research Institute, University of Michigan, Ann Arbor, Michigan (January 1952). 3. Lea, D. E. Actions of Ionizing Radiations on Living Cells. 1947, University Press, Cambridge, England. The Macmillan Company, New York. 4. Manowitz, B. Use of kilocurie radiation sources. Nucleonics, 9 (2), 10 (1951). 5. Proctor, B. E., and Goldblith, S. A. Food processing with ionizing radiations. Food Technol, 5 (9), 376 (1951). CHAIRMAN WIESMAN Thank you, Dr. Brownell. That was a very interesting paper. There is no question but that it behooves the canning industry to follow the results of this work very closely in order to be in a position to take advantage of anything worth-while that might de- velop from it. There are a lot of interesting implications. The next paper will be concerned with sterilization by use of ionization radiation. There has been a lot of work going on for a num- ber of years at the Food Technology Department of M.I.T. The paper, prepared by Dr. S. A. Goldblith, associate professor of food technology at M.I.T., will be given by Dr. Nickerson. Potentialities of Utilizing an Electron Bombardment Treatment for the Production of Canned Meat Products SAMUEL A. GOLDBLITH Over the past few years, it has been demonstrated that destruc- tion of microorganisms in any organic or inorganic medium can be achieved by bombardment with ionizing radiations, irrespective of whether the container holding the medium is of metal, glass, or fiber. For most of the research in this field, cathode rays or beta particles produced in particle accelerators of various types have been used, and canned meat products are among those foods that have received considerable attention to date. 114

In a consideration of the sterilization of meat products by cathode rays a number of factors must be taken into account. The answers to some problems are already at hand, but a number of others remain yet to be solved. The purpose of this paper is to outline the present-day status of the sterilization of canned meat products by high-energy cathode rays and the requirements and methods to meet the objectives in such sterilization. Equipment. The early experiments on cathode ray sterilization were con- ducted with particle accelerators, which were designed primarily for nuclear studies. Consequently, such equipment was of relatively low-power output (500 watts or less) and produced ionizing radiation of moderate energy levels (1 to 3 m.e.v.). More recent developments in particle-accelerator equipment have led to greater power outputs (up to 12,000 watts) but not to greater energy levels (voltage). It has been shown (1) that the potential difference (voltage) through which electrons are accelerated determines the penetration of these electrons in matter, according to the equation: R = 0.542E-0.133 max P where R is the maximum penetration of electrons (cm.) of energy E max (m.e.v.) and P is the density of the absorber (gm./cc.). Electron accelerators more suitable for sterilization purposes have been built and are now available with a sufficient electron "flux" for rapid sterilization at TABLE 1 GENERAL FACTORS OF IMPORTANCE IN ELECTRON ACCELERATORS USED FOR STERILIZATION PURPOSES Factor Remarks Voltage (m.e.v.) Electron beam current (ma.) Total power (watts) Efficiency of utilization (%) Reliability of operation Cost of steri- lization (cents per Ib.) Determine penetration Determines number of electrons per unit of time bombard- ing sample, hence rate of sterilization of material of thick- ness determined by voltage Combination of voltage and current that determines total quantity of material that can be sterilized. Based on inherent variation of ionization in depth of cathode rays in matter Determines how much material needs to be reprocessed; at present appears to be limited, in general, by tube per- formance; dictates number of spare machines required Determined by original capital investment, over-all per- formance of sterilization units, number of units required, cost and frequency of replacement of certain components 115

energy levels up to 3 m.e.v. Particle accelerators have been built to accelerate electrons to higher energy levels. However, these have not yet been built for sterilization purposes. It would be well to define and illustrate the general factors of importance in any electron accelerators, regardless of make, for sterilization purposes. These factors are listed in Table 1 and are discussed below. Voltage. The accelerating voltage required is dictated by the sizes of the conventional containers that are used today. At the present time an upper limit of 3 m.e.v. has been achieved. The degree of reliability of maintaining this voltage with present accelerators at high beam currents appears to be fair. Higher voltages should be obtainable (up to 5 to 8 m.e.v.) with modifications of present equipment and with power outputs high enough for sterilization purposes. How- ever, this situation will require considerable development and cost. Present voltages available in such types of equipment provide facilities for surface sterilization of a number of products and for sterilization of products in containers one inch in thickness or less. This will be discussed later in this paper. Current. The electron beam current is a measure of the total number of electrons accelerated down the tube and available to impinge on the material being irradiated. This current determines the quantity of material—of a thick- ness limited by the voltage—that can be irradiated per unit of time. The re- quirement for steadiness of the beam current is obvious. At the present day, 3 m.e.v. beam currents of 4 milliamperes and slightly higher have been produced. Power output. The product of voltage and current, that is, the power out- put, dictates the total quantity of material that can be treated per unit of time. The manner of presentation of the material of the beam and the efficiency of utilization of the power are also controlling factors. These factors will be dis- cussed separately. A power output of 12 kilowatts (as represented by an ac- celerating voltage of 3 m.e.v. and a tube current of 4 ma.) represents a power equivalent of 12,000 joules per second. On the assumption that a dose of 2x10" rep has been determined experimentally to be the sterilizing dose, and as 1x10" rep is equivalent to an energy absorption of 8.3 joules per gram, 2xl06 rep = 16.6 joules/g. and 12,000 joules per second _ 723 g/sec 16.6 joules per gram ~ f The value of 723 g. represents the amount of material that can be processed per second with a power output of 12,000 watts, if 100% efficiency is assumed. FIGURE 1 lONIZATION IN DEPTH FOR MAXIMUM, MINIMUM, AND AVERAGE DOSES OF ION- IZING RADIATIONS. 04 08 12 ABSORBER THICKNESS 116

Efficiency. In the preceding paragraph, the efficiency of utiliza- tion of the electron beam energy was assumed to be 100 %. Such an efficiency cannot be achieved, however, because of the inherent scat- tering of electrons in matter. Figure 1 represents the well-known ionization-in-depth curve of cathode rays in matter. As has been shown by (4), utilization of the beam is dependent on the thickness of the sample chosen. For example, if a sample of 3/5 Rmax (at 3 m.e.v., Rm»x=1.5 cm. and 3/5 Rn,0x=0.9 cm.) is chosen, the ionization curve shows a minimum dose of 60% at entrance and exit levels of the radiations with the maximum or 100% dose at 1/3 Rnmx. In other words, a variation in dose of from 60'/ to 100% to 60% is present from top to bottom of the sample. In addition, the "tailing" of the ionization- in-depth curve is not utilized. This represents an energy loss of 15% of the total available energy not utilized at all. Of the available 85% of the total energy that is used, the efficiency of utilization is 75% , be- cause of the variation in dose through the sample (2). The 15% of the total energy that is not utilized by the one-di- rection bombardment can be utilized by "crossfiring" or bombarding through two portals of entry, e.g., the top and bottom of a can, when a sample thicker than Rmas is treated. This is advantageous from the viewpoint of product thickness. This can be done by splitting the electron beam and bending it with magnets or by making 2 passes with the cans filled with solid materials, turning the cans over before the second exposure. The efficiency of penetration of the electron beam energy when conventional sardine cans are crossfired is illustrated in Figure 2. It is to be noted that the can cover absorbs a great deal of the energy available as pointed out by (4). With 3 m.e.v. electrons, a steel sardine lOOr 6 8 1.0 1.2 1.4 PENETRATION (cm) FIGURE 2 IONIZATION IN DEPTH IN STEEL SARDINE CANS FILLED WITH MATERIAL OF UNIT DENSITY AND CROSSFIRED BY 3.0 M.E.V. CATHODE RAYS. 117

can filled with material of unit density can be sterilized by crossfiring, with a variation in dose of from only 78% (entrance dose) to 100% at 1/3 Rmai (Figure 2) from each surface to the center of the can. The same result can be accomplished with the same efficiency by 2.6 m.e.v. electrons, if aluminum cans are used, for aluminum has a density only one-third that of steel (Figure 3). The lower voltage requirement is a desirable attribute, because it will allow one to use a given accelerator at lower-than-rated voltage and hence should probably increase the reliability of operation of the machine or permit the use of an accelerator of lower voltage. As higher voltage accelerators for sterilization purposes are dif- ficult to produce without increased costs for development, it is desir- able to use as low a voltage as possible. In this connection, further progress may be expected if plastic films are utilized, because their density is almost unity — in contrast to rigid packages of much higher density. However, further investigation is required to ascertain whether the functional qualities of these films offer as nearly perfect protection for the sterilized products as do rigid containers. Meat packed in conventional cans, e.g., 12 Z oblong cans, would require 6 m.e.v. electrons for crossfiring as shown by (5). An ef- ficiency of beam utilization in depth of 75% should be obtained, espe- cially with means of reducing lateral variation in dose by scanning (6). For realistic purposes, a utilization efficiency of 507' might well be used. The design and development of particle accelerators of such energy levels, with a sufficient flux of electrons, are necessary for con- tainers of greater thickness. The linear electron accelerator may offer a means of achieving such voltages in the near future, if further de- N 100, 80 A H 0 V 2CE R 2.0 ~0 2 .4 .6 .8 1.0 12 1.4 16 PENETRATION (cm) FIGURE 3 lONIZATION IN DEPTH IN ALUMINUM SARDINE CANS FILLED WITH MA- TERIAL OF UNIT DENSITY AND CROSSFIRED BY 2.6 M.E.V. CATHODE RAYS. 118

velopmental research indicates that larger power outputs than are presently available can be perfected with a good degree of reliability. Reliability of operation. With any processing system one must ascertain the reliability of the process. In this particular method, the required reliability of maintaining accelerating voltage and current at needed rated levels is of a high order. A variation in 107' of either of these power components for a given unit of time would require re- processing of the quantity of material treated in that period of time, because a 10'/ diminution of one or the other components would re- duce the dose delivered to the sample by 10'/ and would result in some unsterile products. This factor of reliability is also of importance from another standpoint. The lower the reliability, the more the material required to be reprocessed; hence the greater the number of machines needed for the sterilization process and, therefore, the greater the initial investment as well as the higher the upkeep costs. Cost of sterilization. The cost of the sterilization process by any type of radiation is based on the initial investment required plus some other factors in addition to those previously discussed. The initial in- vestment required, as explained before, is partially determined by the reliability of operation. Other factors, which are common to radia- tion sterilization regardless of the source of the radiation, are as fol- lows : Shielding costs and building alterations Personnel costs Replacement cost of components of relatively short life Monitoring and safety costs Total quantity of material that can be processed per unit of time in the given installation In addition, the obvious factor of dose requirement is also involved in the cost picture. For instance, a dose of 2,000,000 rep for destruc- tion of spore-forming bacteria presents a cost picture much different from that presented by a dose of 100,000 rep for insect destruction. Time does not permit detailed discussion of each of the cost items mentioned above. Summary of equipment factors to be considered. One may sum- marize the equipment factors to be taken into consideration in the radiation sterilization of meat as follows: Particle accelerators for electron acceleration having a range in voltage of from 1 to 3 m.e.v. have been designed and fabricated. A power output of 12 kilowatts at 3 m.e.v. has been achieved. This represents sufficient power for commercial production rates and, therefore, allows a unit container of material to be processed in a fraction of a second. However, the limitations on depth of penetration are present. Higher voltages are possible but require considerable devel- opmental research. 119

Data concerning the reliability of operation of particle accelera- tors under conditions of commercial production, e. g., 8 to 16 hours of continuous operation per day, have not yet been obtained. Proper cost studies must await the solving of the reliability prob- lem. Until this is done, the cost figures should be considered only as rough estimates. The product. Sterilization of canned meat products by cathode rays, insofar as the product is concerned, involved most of the factors that are present in sterilization with isotopic sources of beta- or discussed in detail previously (4, 5), are summarized below. Inoculum. The resistance of a given species of microorganism is of greater importance than the numbers of that species present. For instance, a thousandfold increase in the concentration of bacteria results in only a small percentage increase in sterility dose require- ment, whereas a twofold increase in resistance results in a twofold increase (1007 increase) in the sterility dose requirement. These facts are independent of the source of radiation and apply to any source. Side-effects. Since the beginning of our studies in this field in 1943, it has been known that some undesirable side-effects may be produced in meat and meat products treated by sterilizing doses of ionizing radiations, regardless of the source of these radiations. With meat products, these undesirable side-effects are off-color, off-flavor, and undesirable odor production. A process of addition, in food prod- ucts, of free-radical acceptors prior to irradiation has been developed in these laboratories which has been successful in minimizing some of the undesirable side reactions. However, the results of long storage tests are necessary before any detailed specifications for the process can be set up. With fresh, chopped meats packaged in cellophane and irradiated, a darkening of color develops on storage at refrigerator temperature. Whether this is related to the radiation process or to the inadequacies of the type of package used remains to be investigated. Further fundamental research on the addition of other free- radical acceptors for obviating the undesirable side reactions produced by ionizing radiations is under way in these laboratories. Other meth- ods for preventing these side reactions have been reported recently by Huber, Brasch, and Waly (3), such as the use of different gases or the addition of spices, herbs, and seeds. Enzymes. In the preservation of meat (muscle tissue) by ionizing radiations, it is not considered that enzymes are of importance pro- vided they are not involved in color changes in the product or in ran- cidification of fats. Animal tests. Tests of a nutritional and toxicological nature must be performed with animals before the process can be accepted by the appropriate governmental agencies. These tests should be performed 120

in collaboration with the appropriate agency involved and should in- clude a long-term study of reproductivity effects as well. The package. Those aspects of the package that affect absorption of high-energy radiations have been discussed previously in this paper. There are other aspects that must be considered, however. These are the functional properties of the container and the manner in which these properties are affected by the radiations. The package must not only remain a barrier against microorganisms after irradiation but must also retain its functional properties such as moisture-vapor retention and gas permeability, which must not be adversely affected by the radiations. Under a contract with the Quartermaster Food and Container Institute for the Armed Forces, we are studying the various phases of the effects of high-energy radiations on packaging materials. When one is considering the use of films for the packaging of meat for radiation sterilization, retention of the color of the meat becomes a distinct problem and research is required to solve the problem of color retention. Meat products that can be treated with ionizing radiations loith some degree of success. Promising results indicating some degree of success in meat sterilization by ionizing radiations have been obtained in studies as follows: Surface sterilization of meats such as frankfurts, to increase the keeping time under refrigeration storage. Sterilization of chopped, canned meats in cans or packages. (Thickness limited at present to cans one-inch thick or less.) Pasteurization of fresh, chopped meats. Destruction of trichina in pork (4). Summary This paper has been written in accordance with the title that was indicated by the chairman of this symposium. An effort has been made to present factually the pros and cons of cathode ray sterilization in regard to meat at this time. In summary, it may be said that the sterilization of meat products by ionizing radiations offers a number of problems common to both accelerator and isotopic sources of radiation. It has been clearly in- dicated that there are numerous problems yet unsolved concerning this process and that, to provide equipment capable of wide utilization, developments not yet undertaken from a machine standpoint are neces- sary. It might also be said that the same factors apply to all other suggested means of radiation sterilization and the equipment neces- sary for commercial production of radiation-sterilized foods. Although greater penetration is available with isotopic sources of gamma radiations, beta-particle accelerators today offer a power availability approximating that required for commercial production rates. The reliability of operation of these accelerators has not yet been established, and until this is done, realistic cost figures for the 121

sterilization process will be difficult to calculate. Realistic cost figures for isotopic sources should be equally as difficult to calculate at the present time, because of the unknown cost of preparing and packaging these sources in the multimegacurie quantities necessary for handling even small plant outputs. The present status of radiation sterilization of meat and meat products, insofar as the product is concerned, has been discussed in detail. Although the data presented show that a great deal of research is yet to be done to make this process commercially feasible, a brief glance into the recent past shows that much has been accomplished in the few years that this method has been studied by the relatively small number of investigators in the field. Literature Cited 1. Glendenin, L. E. Determination of the energy of beta particles and photons by absorption. Nucleonics, 2 (1), 12-32 (1948). 2. Goldblith, S. A., and Proctor, B. E. Evaluation of food steriliza- tion efficiency. Nucleonics, 10 (9), 28-29 (1952). 3. Huber, W., Brasch, A., and Waly, A. Effect of processing condi- tions on organoleptic changes in foodstuffs sterilized with high intensity electrons. Food Technol, 7, 109-115 (1953). 4. Proctor, B. E., and Goldblith, S. A. A critical evaluation of the literature pertaining to the application of ionizing radiations to the food and pharmaceutical fields. Tech. Kept. 1, Contract No. AT (30-1) -1164 with U. S. Atomic Energy Commission, January 1, 1952. (NYO 3337). 5. Proctor, B. E., and Goldblith, S. A. Food processing with ionizing radiations. Food Technol, 5, 376-380 (1951). 6. Robinson, D. M. U. S. Patent No. 2,602,751 (1952). CHAIRMAN WIESMAN Thank you very much, Dr. Nickerson. 122

(.iHirliuliiiii Discussion CHAIRMAN WIESMAN I suppose you are all primed with questions. In order to start things off we have a gentleman here who is acknowledged to be an expert in the art of canning. Dr. Ball, will you summarize the high- lights of the meeting so far today? BALL It gives me great satisfaction to see the interest that has come within recent years in the improved methods of canning foods. If you have followed my interests at all during the period I have been active in this work, you know that through all the years, I have been looking forward to the things which may bring into effect the improve- ments in quality of canned food that are possible. The frozen food people are going to have to look to their laurels very diligently because there are qualities in canned foods which they are not able to obtain as yet in frozen food. I think particularly of the stability factors and if we can add to those, great improvements in organoleptic quality, we will have something hard to excel. As we look over the disclosures that we have had today, we can classify the processes in 2 principal categories; those dealing with heat and those that do not deal with heat in the sterilization of food. All of those that use heat are associated, you might say. We can use various methods of applying heat in almost any of the different meth- ods of processing. All we need is to make little modifications of equip- ment to go from one type of heating to another; the object is to produce as rapid heating as possible because fast operation, fast effect, is of prime importance in heat processing. In the methods in which heat does not play a part, those described in the last 2 papers, for ex- ample, time, from the standpoint of its effect on quality, is not im- portant; of course, it is important from an economic standpoint. We know that we can never think of a commercial operation which would require what Dr. Nickerson showed is required as to the inten- sity of radiation. It would not meet the requirements of commercial operation because of its not being economically feasible. In those types of treatment we have to think primarily from the standpoint of economics, whereas, in the heat and the heat methods, the economics are of less importance. To start off with a question, I would like to ask Dr. Doty, in con- nection with organoleptic qualities of food heated dielectrically and that heated by steam methods, what kinds of steam methods you were referring to—whether they were fast heating or not? DOTY In the case of the pork luncheon meat, comparison was made between dielectrically processed meat which we prepared and the pork luncheon meat as processed at the Food and Container Institute using 123

the standard procedure required for the product. I can't tell you the F0 value for it, but it was a sterilization sufficient to hold the product without refrigeration. It was a slow retorted sterilization. CHAIRMAN WIESMAN Thank you very much, Dr. Ball. We certainly appreciate your comments. May we have some questions from the floor? A. C. EDGAR (Wilson & Company) On sterilization of units—what was the largest size that you worked with, and if you had a large unit, for example, a 10-pound ham for commercial use, would chilling of that product be a problem ? DOTY On our work with hams, we were processing 11-pound boned ham units. Actually, with the oscillator capacity which we have, even larger units per run would be better because of increased resistance offered by a longer capacitance. Actually, since the ham only grows so big you would have to do it in multiple units or use a smaller oscillator to get more efficient processing. We do not have the figures on the cooked capacitance loss, Mr. Edgar. As a matter of observation, and perhaps Mr. Peterson can check me on this, I think we probably have no more loss and perhaps less than you would have under normal pasteurization procedures as carried out at present because of the speed with which the ham is heated. MANDELS I wonder whether one can actually take a complex material like meat which contains proteins and all kinds of other constituents and actually store it at 100°F. for a matter of a year or 2 without getting decomposition. Suppose you took a simple protein like gelatin or some- thing like that, would that be stable under such conditions? CHAIRMAN WIESMAN Who would like to answer that question ? STUKIS I presume it was directed at me. I can't answer the second part of that question with regard to gelatin because I haven't conducted such studies. But these comparisons that we did make, you see, were all relative. In other words, how good would a ham processed by this method be stored for one year at 100°F., say, compared to luncheon meat or chopped ham, processed in a conventional manner, stored for a like period of time at the same temperature. We would assume, and we have found, that conventional methods with pork luncheon meat or chopped ham give better results on color, flavor, texture, and slice- ability than we obtained on this particular study with this ham. 124

I don't know whether this answers your question or not. You see, it is all relative. It doesn't stand by itself. It stands by comparison with some other item. In other words, it didn't store quite as well as some of the other items we have looked at and examined. GARDNER I suspect that as we are able to lower our process and obtain a better product initially, there will still be certain chemical changes which are not inhibited, which are now inhibited by the severe process. HARRY SPECTOR (QMFCI) As a contribution to the over-all nutritional adequacy of the op- erational ration, canned meats have an important function. But we have observed a loss of thiamine, as high as 70% of the original con- tent, on processing, and we get an additional loss of 50% during high- temperature storage. In rations which are apparently adequate by calculation, we find that when we feed them to laboratory animals they are inadequate and require supplementation with proteins and vita- mins to promote normal growth. In listening to these papers, it seemed that Mr. Smith was the most optimistic about the commercial feasi- bility of'his process. I wonder whether any studies have been con- ducted on the effect of that particular process with regard to retention of nutrients. SMITH We hope to have some, but at the moment we do not. BALL There have been studies made on foods sterilized in similar fashion, and the results of those studies should apply to foods processed by our methods also. I refer to a comparison between -the short-time sterilized foods and the food sterilized by longer heat processes. CHAIRMAN WIESMAN I wonder, Dr. Morse, if you could tell us something about the effect of ordinary steam processing on nutritive value of meats. MORSE In addition to improvement of texture and taste quality, we should stress very heavily nutritive retention. I think we ought to hit it harder than we are doing at present. One of the reasons we may have dif- ficulty with acceptance is the old business of people being inclined toward food that "does them good." We may be missing that point altogether. They aren't getting the nutritive value in these long-stored meats they should be getting and therefore they are rejecting them and searching for something which will supply the nutritive value. That's not much of an answer, but it is the best I can give. 125

CHAIRMAN WIESMAN Dr. Brownell, has any kind of work been done on the effect of the fission product treatment on the wholesomeness of canned meats ? BROWNELL The wholesomeness of irradiated food is the problem that we are about to investigate under this animal feeding experiment. As I stated earlier, we have only run one short experiment of 6 weeks. We hope to conduct this next experiment for a period of at least 2 years with 4 generations of animals or more; we hope that that will establish the wholesomeness—the ability of irradiated food to support normal growth without any undesirable autotoxic effects. It will probably be at least 2 years before we have an answer. CHAIRMAN WIESMAN How do you feel about it, Dr. Nickerson? There has been a lot of work on ionizing radiation and vitamin retention. NICKERSON There has been work done, and there is apparently not a great deal of loss of vitamins, due to irradiation. EDGAR I would like to comment on storage of products processed rapidly with agitation cooking or end-over-end cooking. It has been found that although the flavor doesn't seem to change, particularly, the texture does. In other words, when a product like spaghetti and meat is considered the spaghetti gets rather soft after a period of one year or possibly sooner at elevated temperatures; thus, there is some change even though we have an advantage at the start. We do get some change after prolonged storage, and particularly at 100°F., which is a very severe temperature for storage of meat products. I might add that we do not have any nutritive data on the end-over-end material as yet. T. C. KMIECIAK (QMFCI) When material is sterilized by gamma radiation, do you have residual radiation from that particular product which in turn is effective in killing? With this cold type of sterilization, you have the possibility of mutant strains being developed as we have in antibiotics —what will the result be? BROWNELL In answer to your first question, there has been no evidence of any residual radioactivity using either gamma or beta radiation. To induce residual activity would require bombardment by neutrons. 12G

Regarding the development of mutant strains, Dr. Gaden at Columbia has done some work along these lines and has exposed micro- organisms to radiation, the dose sufficient to kill, say 99% of the organ- isms. He has then cultured the remainder and repeated his experiment until he has developed strains that have greater resistance. You would not expect, however, in the irradiation process as used with food to have conditions suited to propagating resistant strains. CHARLES NIVEN (American Meat Institute Foundation) What proportion of the canned hams used in the Institute experi- ment that were sto*red at the higher temperatures showed gross evi- dence of microbial spoilage as judged by gassiness or digestion of gelatin, foul odor, digestion of the meat, or perhaps a large number of bacteria showing up on direct smears? STUKIS To the best of my knowledge there was no gross evidence of spoil- age such as extremely foul odors or digestion of the meat. Hams stored at 100°F. evidenced an increase in count over the first 3 months. By the time the 10th month had arrived, evidently the growth cycle had been completed, and the counts were greatly reduced. Perhaps Dr. Rayman would care to add something to that. MORTON M. RAYMAN (QMFCI) Of all the cans we examined only one was slightly swollen. There was no evidence of spoilage in the can. The bacterial picture has been described. GEORGE F. STEWART (University of California) To go back to cold sterilization for a point of clarification—is it true that regardless of whether it is a beta or gamma radiation it requires the same amount of reps to achieve a kill of spores or vegeta- tive cells ? Also, what is the relationship with enzyme destruction ? BROWNELL Our data indicate the same order of magnitude of radiation re- quired using gamma rays in the destruction of microorganisms as that reported by those working with beta rays. As to enzyme destruction —enzymes apparently are much more resistant to radiation than are microorganisms; it takes perhaps 10 times the dosage or more to destroy certain enzymes than it takes to destroy the microorganisms. However, despite this fact, meat sterilized with radiation does not seem to undergo enzyme degradation as shown by the fact that the meat stored for several months is not liquid. It is still in about the original state. 127

STEWART There are many enzyme systems not involving liquidation of meat, however, which cannot be overlooked. NICKERSON That's true. The only thing I would add to what Dr. Brownell has said is this: If you have your enzymes in pure solution, you can destroy them very readily with ionization radiation, but in food prod- ucts they appear not to be affected to any great extent. GARDNER Would it be in order to ask what the mechanics are, that is, what does the radiation do to the bacteria? BROWNELL The process by which microorganisms are killed by radiation is not very well understood. Ionization radiation has the ability of knocking electrons off the molecule and apparently certain molecules or groups of molecules in the organism are sensitive to such an effect; there has been proposed a target theory that if a certain num- ber of these sensitive molecules are bombarded by radiation, the organism will die. Perhaps Dr. Nickerson could add more to that. NICKERSON I don't know that I can add much—it is all theory, anyway. It is something similar, perhaps, to Ryan's theory that some protein in the gene is necessary for reproduction. That's just theory, of course. A. M. SMOLELIS (Armour & Company) Have you tried cell-free solutions where you have the enzymes in suspension, for example, and tried to irradiate those? JOHN GRAIKOSKI (University of Michigan) Enzymes in diluted concentration are not very radio-resistant, but as you increase the concentration they are more resistant. Enzymes in tissue are very radio-resistant. The enzyme is in a bacterial cell. It will not reproduce and produce a colony, but Proctor and Goldblith have shown enzymatic activity in bacterial cells still continues even after exposure to sterilization dosage required to prevent their (the bacteria) forming colonies. The work was done with E. coli. SPECTOR With reference to the canned meat items in the C Ration, the chart shows some 10 canned meat items, but the menu is so arranged that the C Ration consists of 6 different menus and 3 different meat items in each menu. So we have only 10 meat items to use where we 128

need 18 meat items; within the existing 6 menus we have some repeti- tion. Also, some of the items that are used in the C Ration are used in the B Ration, the 5-in-l, and perhaps in the In-Flight. We have been asked on occasion to develop new rations, and we have done that, to meet new tactical situations, but the limiting factor in all of this is the number of available canned meat items. The danger that we run is that even though we may have something like 13 or 14 operational rations, from the standpoint of the soldier who is consuming them, no matter whether he is on the B Ration or C Ration or the Assault Pack or In- Flight—he is seeing the same meat item in just a different size can. From the menu-planning standpoint, therefore, there is a great need for a greater variety of meat items. We are very happy to see that there are some 17 or 18 items on the horizon that we can put into the rations, and that work is going on to increase the number even beyond that. LT. COLONEL GEORGE F. McANENY (QMFCI) I would like to accentuate one thing, if I may, and that is we can all sit down around the table in the Institute, and I think a lot of the people here have done so, and try these canned rations. We think they are pretty good, but when you have to subsist upon canned meat for days at a time, it can become pretty tiresome. I am sure you mem- bers of industry are well aware of the fact, even though your con- centration is primarily upon fresh and frozen meats, that fresh meat is what the American people want. I feel, and I think that all the Armed Forces feel, that a soldier, when he puts on the uniform, is still the American people. It doesn't make any difference. He still would like the frozen and fresh meat, but we must remember there are many times when he cannot get it, and what we would like to get from you people is better canned meats. That is the principal reason for asking for that advancement of canned meats. CHAIRMAN WIESMAN Thank you, Colonel. MEYER I didn't quite appreciate the advantage of the Smith-Ball process over, say, the standard, at least, the agitated retort process. If you have a piece of meat in a can and don't have it in a retort, but heat it in a room which is pressurized, is the rate of heat penetration in any way enhanced? SMITH You can heat the product up to sterilization value with any method that achieves the highest rate of heat penetration, and in the smallest particle size which is used in the product; the pressurized chamber raises the boiling point, raises it up to the sterilization point before 129

you put the product in the can. Then you put it in the can and seal it at that temperature. MEYER Would the intention then be, say in the case of meat chunks, to agitate them while they are being cooked so that you get a greater heat penetration? If you had a large vessel full of compact meat, I suspect the rate of heat penetration wouldn't be any more advantageous than it is in a No. 10 can or any large can in a steam retort. SMITH You could heat those meat chunks in an atmosphere of steam where the temperature of the surface would always be that of the steam. If you leave them in a can and you have 2 or 3 pieces in there, the inner face temperature would be lower than at the surface or the rate would be lower. R. A. LARSEN (QMFCI) It is my understanding that meat and other products deteriorate in storage for 2 reasons—the growth of microorganisms in the meat products and also because of the action of the enzymes which are in- herent in the meat. Yet, in recent years, I have been reading some publications which have made me wonder if the enzymes within a meat product really would cause deterioration. I would like to ask whether, if you prepared meat under absolutely aseptic conditions, it would be necessary to store it under refrigeration or could you store it at normal room temperatures without refrigeration? MORSE There is some work being done at Ohio State that hasn't been introduced in the meeting—that is, where animals immediately after slaughter are perfused with an antibiotic solution through the venous system, producing in effect a sterile carcass, internally, at any rate. This meat was hung at room temperature for 11 days without spoil- age, and the enzymatic processes do go forward. You can take a pretty tough critter and make a fairly reasonable piece of tasty meat out of it. This is not a direct answer to your question, but I think it gives some of the clues that we are seeking. Incidentally, in conjunction with that work, there was a tech- nique used that I think may be of some value to some of you. They reasoned that if there were to be microorganisms circulating through the animal tissue, a good logical place to be on the lookout would be the nodes of the lymph system. They developed a technique for iso- lating, under fairly sterile conditions, the nodes from the animal tissue, immersed this in 95'/ alcohol and set it aflame, and then went back at it again with sterile instruments. They developed what I think is probably a quite reasonable sterile technique for looking for bacteria 130

within the tissue and found a lot of them. The enzymatic processes do go forward and even under quite sterile conditions. Incidentally, you could take this meat at room temperature, and leave it on the table for a week, and the outside would turn jet black. If you cut it away, it was perfectly sweet smelling and could be eaten; I ate some and I am here to tell about it. LARSEN I would like to ask one other question. I was talking with Dr. Wilt Hachuger of Electronized Chemicals. He told me that with the capacitron and very slight penetration into the meat, he could take a thick piece of beef steak and sterilize it, essentially, just the surface, not penetrating the enzyme systems within the tissue, and that meat could be stored indefinitely at room temperature. Then there is the work they are doing at Notre Dame, growing animals under aseptic conditions. It is my understanding when those animals die, they do not decompose. If you produced meat under strictly aseptic conditions, would you have to worry about storage properties? CHAIRMAN WIESMAN Would anyone else like to comment on that? RAYMAN I was going to make the same comment that Dr. Larsen did a minute ago about the germ-free animals. I think there is a difference there. The enzyme reactions that Dr. Morse referred to as continuing and the enzyme reaction that Dr. Larsen refers to as not continuing are probably due to the question of the liberation of the enzyme from the tissue in the slaughtering and meat preparation as opposed to the natural death and the intact enzyme in the tissue. In one case you have it released and have a chance for it to work; in the other case, it just doesn't seem to do anything. I don't know if that is the ex- planation. BALL Have they determined anything at Ohio State as to the termina- tion of this enzyme action? How long is it going to continue? Under what conditions will it affect the meat? Do they know anything about that? MORSE Direct answer, no. I think what happens, though, is that eventually spoilage begins, and I don't know how long you would have to store it to determine what the enzymatic problem would be—maybe 6 months—in which case you couldn't very well have it sitting around that long. 131

STEWART I think there is ample evidence that enzyme systems continue to operate after death and in the absence of bacterial growth. You can go back to 1900 and prove this. You don't have to take this year's data to do that. The important thing is whether the changes that go on are important changes from the standpoint of eating quality. Cer- tainly, we know the glycolytic system comes to a halt in a few days with the establishment of the lactic acid, and so on; there is also evidence that the proteins are broken down, because some of those early studies, where they kept them under conditions where you did not get growth, eventually end up with essentially a very soft or almost a jelly condition in the meat. So I don't think there is any question about the matter of whether the enzymes act or not. The question is whether the time limit imposed there is important. This business of keeping them indefinitely is a little silly because indefinitely is an awfully long time. MORSE Fortunately, it looks as if just the right ones keep on growing a little bit. CHAIRMAN WIESMAN There is the problem—I heard the Food & Drug is not going to permit the use of antibiotics in food. What we may have here is a lot of good, fundamental information. MORSE The rest of that story—they are unable to detect any of the antibiotics within 48 hours after infusion. Whether that validates the use of antibiotics or not, I don't know. CHAIRMAN WIESMAN It is a legal problem, I guess. NIVEN I wonder if some factors more important than enzymatic or microbial may be concerned here as evidenced by the work of Stukis and co-workers, that is, of the browning reaction that goes on at elevated temperatures at storage, which would markedly affect the flavor as well as the appearance. STEWART I think that is an extremely good point. Dr. Ayres and I did some work on chicken meat at one time in which we inhibited bacterial growth quite effectively. One of the first things that showed up was rancid fat flavors which you never get ordinarily in chicken meat. So I think you do run into those things. 132

GARDNER It might be interesting to note that the same odor, though to a lesser degree, and the same flavor difficulties we encountered in Mr. Stukis' experiment are being encountered in experimental work on de- hydrated meat, indicating that regardless of how the meat is processed, you may have the same problem. MISS C. WALLIKER (QMFCI) We were talking about aseptic slaughtering. I was wondering if that doesn't raise a question. How is that going to affect the aging process ? MORSE That was the basis for this work, actually. It was an effort to do a round tenderizing. I think it will accomplish the same thing as tenderizing. You are able to elevate the temperature of storage and decrease the storage time used for tenderizing meat. Is that what you have in mind ? By raising storage temperature, the time required for aging is greatly decreased. Like any other chemical reaction, it proceeds at a more rapid rate. The aging time is greatly decreased. DOTY Actually, at least the assumed situation that occurs during aging, as far as tenderizing is concerned, is the result of the enzyme sys- tems, particularly the proteolytic system in the tissue, and not systems which are contained in the bacteria or yeast which contaminate the carcass. If you keep down the contamination and speed up the enzyma- tic processes by increasing the temperature, then you should get a more rapid and complete aging without the undesirable effects of bacterial and yeast contamination. MORSE As to solid chunks of meat, and the interesting part, the heat induced by the electrical resistance of such material—would you say that the same relationship would hold true on material that had fluid in it—for example a beef fluid? Would resistance be an important factor? DOTY Actually, the proportions of moisture in fat and in protein in- fluence the proportion of energy which heats by means of the capaci- tance of the material and resistance in the material, so if one were to increase the moisture content, one should increase the capacitance and decrease the resistance. With an increased moisture content you expect to get a higher proportion of capacitance through dielectric heating, if you please, and less and less resistance heating. If you use meats of different fat content, then because the fat and moisture 133

content are essentially inversely proportional to each other, you vary the moisture content in the same ratio. In the heating which we have done with ground beef at 2 different fat levels, at 12% and 25%, then, we have essentially used 2 different moisture contents, and we get essentially the same type of heating. In the process we use we are not able to distinguish in the process itself the difference between the heating due to capacitance and heating due to resistance, so I can't absolutely answer your ques- tion. I am giving you what I think theoretically should be the case. But I think you would get essentially effective heating in something like a beef stew where you had a mixture of moisture and particles. GARDNER Have you ever done any inoculating tests—actually inoculated P.A. 3679 to determine the recovery? BOLANOWSKI Yes, we have. We inoculate but let somebody else do the deter- mination. We are not staffed with that type of personnel. We do make inoculative tests. We go to the level below and above to make sure. We first test to make sure the inoculum is active. MEYER There has been a lot of concern about enzymes and the destruc- tion of them by the new methods of sterilization. What's the status of vitamins? CHAIRMAN WIESMAN Dr. Nickerson stated, from the standpoint of ionizing radiation, that they were not destroyed, but they have no storage studies. Dr. Brownell, I believe, said that that work is just under way now. BROWNELL There is some destruction of vitamins by radiation. Ascorbic acid in weak solution is readily destroyed by radiation. In the presence of other materials in food, it is protected. Ascorbic acid protects niacin. Niacin protects ascorbic acid, so in foods you would not expect to have perhaps serious vitamin loss as a result of radiation, but there will be some. We haven't investigated that phase of it to any extent, but we thought it not advisable to irradiate the vitamin supplement in the diet. Also, there is some formation of peroxides in the unsaturated fats as a result of irradiation, and in some feeding experiments it has been shown that there might be a vitamin E deficiency. Therefore, we decided not to irradiate the fats that were added to the diet. 134

KMIECIAK In the chamber used in the Smith-Ball process you duplicate conditions a submarine has gone through; the submarine command has set up a limit of 5 hours work per day. Now are you assuming your people can work a full 8-hour day under those pressures? SMITH We didn't mention submarines. We said divers. A submarine is essentially at atmospheric pressure. I think there are 6 states that have laws governing the operation of personnel at elevated pressures, and all of those states will permit a normal 8-hour working day at 20 pounds pressure. KMIECIAK In keeping with that, you have odors coming off some of these foods that do diffuse away from your blowers. What is the concentra- tion of that after, say, an 8-hour run? Overpowering? SMITH No. We are continually introducing air for ventilation purposes far in excess of normal ventilation. We are introducing about 150 cubic feet per minute in a chamber for 2 people, so I think the con- tinuous introduction of fresh air is far in excess of what would be required for normal ventilation. GARDNER Mr. Chairman, on behalf of the Quartermaster Food & Container Institute I would like to thank each of the individuals who prepared and presented papers; particularly, I would like to thank the National Research Council for making it possible for this symposium to be conducted. I would like to thank each one of you who attended for your contribution. The Quartermaster Food & Container Institute will do its utmost to utilize the information and advice that has been given in the last 2 days. Thank you, Mr. Chairman. CHAIRMAN WIESMAN Thank you very much, and thank you all for your kind attention. (The meeting adjourned at 4:15 o'clock.) 135

Armed Forces Food and Container Institute (U.S.) The quality and stability of canned meats

ADVISORY BOARD ON QUARTERMASTER RESEARCH AND DEVELOPMENT Chairman: GEORGE D. BEAL, Director of Research Mellon Institute of Industrial Research Executive Director: W. GEORGE PARKS COMMITTEE ON FOODS, 1952-53 Chairman: GAIL M. BACK, Director of Food Research Institute University of Chicago George S. Garnatz Emil M. Mrak Director, The Kroger Food Foundation Professor of Food Technology University of California W. F. Geddes Chief, Division of Elmer M' NelsOn Agricultural Biochemistry Chief, Division of Nutrition University of Minnesota Food and Drug Administration Wendell H. Griffith Chairman, Department of Physiological Chemistry School of Medicine University of California Guido E. Hilbert Chief, Bureau of Agricultural and Industrial Chemistry U. S. Department of Agriculture Reid T. Milner Director, Northern Regional Research Laboratory U. S. Department of Agriculture A. N. Prater Vice President, Gentry Division Consolidated Foods Corporation B. E. Proctor Director, Food Technology Laboratories Massachusetts Institute of Technology H. E. Robinson Assistant Director of Laboratories Swift and Company SUBCOMMITTEE ON ANIMAL PRODUCTS, 1952-53 Chairman: HERBERT E. ROBINSON, Assistant Director of Laboratories Swift and Company Daniel Brady Department of Animal Husbandry University of Missouri Carl S. Pederson New York State Agricultural Experiment Station A. R. Winters Poultry Department Ohio State University Clarence K. Wiesman Armour and Company

Quality and Stability of Canned Meats: A Symposium Sponsored by the Quartermaster Food and Container Institute for the Armed Forces, Quartermaster Research and Development Command, U.S. Army Quartermaster Corps, Palmer House, Chicago, March 31 - April 1, 1953 Get This Book
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