food preservation, methods of preparing food so that it can be stored for future use. Because most foods remain edible for only a brief period of time, people since the earliest ages have experimented with methods for successful food preservation. Among the products of early food conservation were cheese and butter, raisins, pemmican, sausage, bacon, and grain.
As scientific investigations regarding the causes of food spoilage were undertaken, they pointed the way to a wider application of methods already in use and to the discovery of new ones. Before 1860 changes in food were explained on the theory of spontaneous generation. Pasteur demonstrated that ferments, molds, and some forms of putrefaction were caused by the presence of microorganisms widely distributed in the environment. Since these microorganisms are the main cause of food spoilage, food preservation depends on rendering conditions unfavorable for their growth. Processes of preservation may be generally classified as drying, heating, refrigeration (see also frozen foods), and the use of chemicals or other particular agencies.
Drying and Heating
The most ancient method is drying, and it was employed early for fruits, grains, vegetables, fish, and meat. It was sometimes combined with parching, as in the oatmeal of Scotland or the corn of the Native American. Modern applications of this ancient device are seen in dried or dehydrated fruits and vegetables, milk, meat, and eggs. A more recent variation, known as freeze-drying, is now being used on such foods as instant coffee, meat, orange juice, and soup. The early method of drying was by direct exposure to the sun's rays; in modern industry the process is hastened by complex apparatus and by chemical agencies. The use of sugar was early combined with drying. Smoking, a method used mainly for fish and meat, combines the drying action with chemicals produced from the smoke, which form a protective coating. The process of heating was used centuries before its action was understood (see canning). One of the most important modern applications of the heat principle is the pasteurization of milk.
In modern food preservation, preservatives function in two ways. One is by delaying the spoilage of the food, while the other is by ensuring that the food retains, as nearly as possible, its original quality. The first method includes the use of sugar (see jelly and jam), vinegar for pickling meats and vegetables, salt (one of the oldest preservatives), and alcohol. Good wine will keep almost indefinitely, and fruit placed in a 15% to 20% alcohol solution (brandying) is well preserved. The second method includes the use of ascorbic acid (which prevents color deterioration in canned fruits), benzoic acid, sulfur dioxide, and a variety of neutralizers, firming agents, and bleaching agents. The excessive or unacknowledged use of these chemical agencies has been legislated against by most governments.
Exclusion of Air
The exclusion of air, nowadays accomplished by hermetic sealing, is an old device, formerly practiced by pouring hot oil over potted meat or fish, by coating or mixing food with melted fat, as in pemmican, or by burying vegetables in the earth or in sand. The use of melted paraffin achieves the same result. Eggs may be preserved by preventing air from penetrating their porous shells, usually by coating them with an impervious substance.
Irradiation has also been used successfully to destroy many of the microorganisms that might cause spoilage in food. Irradiation has been declared safe by the Food and Drug Administration and World Health Organization. Thus, despite opposition from those who fear that health hazards from its use will be discovered later, this method is gradually gaining acceptance.
See G. Borgstrom, Principles of Food Science (2 vol., 1968); N. W. Desrosier, The Technology of Food Preservation (3d ed. 1970); S. Thorne, The History of Food Preservation (1986).