National Academies Press: OpenBook

Dehydration and Compression of Foods (1982)


Suggested Citation:"RAW MATERIALS AND PRODUCT PREPARATION." National Research Council. 1982. Dehydration and Compression of Foods. Washington, DC: The National Academies Press. doi: 10.17226/18526.
Page 17
Suggested Citation:"RAW MATERIALS AND PRODUCT PREPARATION." National Research Council. 1982. Dehydration and Compression of Foods. Washington, DC: The National Academies Press. doi: 10.17226/18526.
Page 18
Suggested Citation:"RAW MATERIALS AND PRODUCT PREPARATION." National Research Council. 1982. Dehydration and Compression of Foods. Washington, DC: The National Academies Press. doi: 10.17226/18526.
Page 19

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RAW MATERIALS AND PRODUCT PREPARATION The type of raw material selected will have some effect on the pro- cedures used for water removal and compression. Structural, chemical, and composition differences will add their individual unique require- ments. Because of their high sugar content, fruits present technical challenges that vegetables do not. Fat content and fiber orientation of meats will influence dehydration and the success of compression. The most appropriate methods for water removal—freeze-drying, air-drying, or other methods or combinations—have not been resolved. Finished product performance and acceptance exert the greatest influence on which raw material and preparation sequence is used. Although economics is also very important, if performance and acceptance are achieved and a definite military or consumer need demonstrated, economic issues can be resolved in favor of product quality and performance as measured under actual operational con- ditions. Frozen fruits and vegetables as starting materials for dehydrated and compressed foods can be selected from existing inventories of frozen commodities or from contracted crops that would be "tailored" specifically for freeze-dried and compressed products. Both sources have been used for the preparation of small quantities for the develop- ment stage. Frozen fruits and vegetables are generally available in bulk individually quick-frozen form at a reasonable cost. Availability and price, along with the qualities of the fresh form can be very sig- nificant advantages if not outweighed by limitations of commercial style or form, level of blanching, variety, and absence of sulfite treatment. Tailored raw materials can be used if one or more of the following constraints are met: The higher cost is justified by superior quality and performance. A reliable source of supply exists. The "new" variety has other uses. New or modified manufacturing operations are minimal. The market size remains significant. Freezing is used to ensure a supply of starting material because of: 17

18 Seasonality, Perishability, Geographic location, Production schedules, and Capital investment needed to prepare raw ingredients. Procurement methods may not allow sufficient lead time to obtain tailored seasonal plant products. Thus, even if research identifies a highly desirable variety it may not be used. Nonseasonal items are more susceptible to optimization by tailored procurement. Tailored nonseasonal raw materials can be purchased on a more rational cost- benefit basis throughout the year. Dehydration, compression, and subsequent reconstitution of a food item cannot be expected to improve its flavor, color, or texture. It must possess acceptable characteristics at the start. Some varieties of vegetables and fruits retain their flavor, color, and texture better than others during dehydration, compression, and reconstitution. The varieties of vegetables and fruits now being grown for the frozen food market are, unfortunately, not always the best varieties for freeze- drying. If they were, it would simplify the development of the market potential for freeze-dried and compressed foods. The size of the market at the present time does not justify an investment by a dehydration-compression company in costly varietal development and testing, and in preparation and freezing equipment that would remain idle during a large part of the year. A freezing company might be willing to freeze a special batch of vegetables or fruits for a freeze- drying concern but the order would have to be fairly large. A company that freezes half a million kilograms (a million pounds) of vegetables per day must make special provision to handle an order for the same quantity of a special variety used by a freeze-drying company. In principle it should be possible to work out an arrangement with food- freezing companies for the freezing of optimized varieties of vegetables and fruits given sufficient time. Such a step would not only make it possible to take advantage of the special characteristics of "tailored" varieties of vegetables and fruits (such as moisture, sugar, salt, starch, and fiber content, as well as color, flavor, and texture) but would also make it possible to take advantage of special prefreezing treatments (sulfiting and various types of blanching to control color, flavor, texture, and storage stability). Some vegetables rehydrate more easily if they are allowed to mature somewhat longer before harvesting but the increase in fiber that results may reduce their acceptability by the consumer. The trade-offs among the various characteristics of a food item to be dehydrated and compressed must ultimately be determined by the user. The military user may prefer a set of characteristics different from the civilian consumer's. The different types of civilian consumers (institutions, restaurants, survival groups, hikers, campers) may have requirements and preferences that call for different trade-offs among cost, flavor, texture, color, or storage life. In any case, military requirements based on actual operational conditions must be met.

19 Research is required to obtain fundamental understanding of the relation between rehydrated quality and structural and chemical com- position of food items being used or considered for the dehydrated and compressed food market. Structural and chemical composition determines not only the quality of an item (flavor, texture, color) but also the way it dehydrates and compresses. The high fructose and glucose contents of fruits, for example, make dehydration difficult and the product sticky. The development of varieties high in sucrose would simplify the dehydration process and improve the end product. Size, shape, and uniformity are important factors in the dehydration and compression of vegetables, fruits, meats, and other food items. Some items (potatoes, onions, meats, apples, strawberries, and mushrooms) that will not dehydrate and rehydrate satisfactorily when processed in large chunks will do so when they have been cut, sliced, diced, flaked, or granulated into thin enough or small enough pieces. A short diffusion path greatly enhances moisture uptake. It is important, however, that the item retain its identity. Some items (peas, beans, kernel corn, cherries, and blueberries) cannot be cut or sliced into small pieces without losing their acceptability. Meat and chicken can be ground or flaked and served in patties, soups, sauces, and rice dishes. Fish can be ground or flaked and served as fish balls. Potatoes can be diced or sliced, flaked for potato chips, or riced for hash-brown potatoes, potato pancakes, and mashed potatoes. Onions can be sliced and served as rings or granulated and served in patties and soups. Carrots can be sliced, diced, "shoe-stringed," and shredded, and green beans can be cut in various ways. Peas, beans, cherries, and blueberries are being left uncut to re- tain their identity but must have their skins pierced or slit to enable dehydration at a reasonable rate. Corn kernels have an end sliced off when cut from the cob, but care must be taken in the stripping process. If too deep a cut is made, some kernels will be whole and not dehydrate satisfactorily. It is important for both the dehydration and compression stage that the size of the pieces in a batch be uniform. A uniform size will enable a more rapid dehydration, better control of the compressed product, and a better rehydrated product. The opportunity to combine restructuring and reformulation of cut pieces with dehydration methods other than freeze-drying should be exploited. Specially formulated air-dried components may allow sat- isfactory compression and rehydration without freeze-drying.

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