Lactic acid fermentations are used worldwide to produce foods such as sour cream, yogurt, sauerkraut, kimchee, soy sauce, and pickled vegetables of all kinds. Except for making sourdough bread, it is so far not used widely to "sour" cereal products. But in Africa it is traditionally used to flavor and preserve porridges and to produce popular foods such as bogobe (sour sorghum porridge) in Botswana, nasha (sour sorghum and millet porridge) in the Sudan, and obusera (sour millet porridge) in Uganda. People in many parts of the continent prefer the sharp flavor of these fermented porridges.6
Despite its almost complete neglect by cereal science, acid fermentation is yet another process for upgrading a grain's taste and nutritive value. For the food supply of Africa, it is particularly promising. The lactic acid fermentation process is well known. It is generally inexpensive and requires little or no heating, making it fuel efficient. It yields highly acceptable and diversified flavors. And it usually improves nutritive value.
It is commonly used in households (at least throughout eastern and southern Africa) and remains one of the most practical ways to preserve food for hundreds of millions of hungry people who cannot obtain or afford canned or frozen foods.
Lactic acid fermentations make foods resistant to spoilage, thereby performing an essential role in preserving wholesomeness. The bacteria rapidly acidify the food to a pH so low that dangerous organisms are no longer able to grow. They also produce hydrogen peroxide, which kills organisms that cause food spoilage (the lactobacilli themselves are relatively resistant to hydrogen peroxide). Certain lactic bacteria (notably, Streptococcus lactis) produce the antibiotic nisin, active against gram-positive organisms. Others produce carbon dioxide, which also helps preserve foods, notably by displacing oxygen (if the substrate is properly protected).
The course of the fermentation can be controlled by adding salt. Salting limits the amount of pectinolytic and proteolytic hydrolysis that occurs, thereby controlling softening (as well as preventing putrefaction).
Although fermented porridges were once extremely popular in rural Africa and are still widely consumed, their popularity appears to be declining. Some consumers are turning to alien alternatives that are widely advertised, such as tea or carbonated drinks. In many districts, farmers (as we have noted earlier) are giving up sorghum and millet and are growing maize. And in others, people are said "to lack the will and the interest" to prepare traditional fermented porridges.
The use of such fermentations to make baby food is discussed in Appendix D.