canning, process of hermetically sealing cooked food for future use. It is a preservation method, in which prepared food is put in glass jars or metal cans that are hermetically sealed to keep out air and then heated to a specific temperature for a specified time to destroy disease-causing microorganisms and prevent spoilage. Low-acid foods, such as meats, are heated to 240°–265°F (116°–129°C), while acidic foods, such as fruits, are heated to about 212°F (100°C). Canning was invented in 1809 by Nicholas Appert. The process proved moderately successful and was gradually put into practice in other European countries and in the United States. Glass containers were used at first, but they proved bulky, costly, and brittle. Early canmaking was slow and expensive; sheets of tin were cut with shears, bent around a block, and the seams heavily soldered. A good tinsmith could make only about 60 cans a day. The industry began to assume importance with the invention in 1847 of the stamped can. Because of the food requirements of soldiers during the U.S. Civil War, considerable amounts of canned meats and vegetables were produced. Salmon from the Columbia River was canned in 1866 and salmon from Alaska in 1872. A machine for shaping and soldering was exhibited in 1876 at the Centennial Exposition at Philadelphia. The open-top can of the 20th cent., with a soldered lock seam and double-seamed ends, permits easy cleaning and filling. Cans used for foods that react with metals, causing discoloration (usually harmless), may be coated with a lacquer film. Highly specialized machinery, knowledge of bacteriology and food chemistry, as well as more efficient processes of cooking, have combined to make the commercial canning of food an important feature of modern life. The range of products canned has increased enormously and includes meat and poultry; fruits and vegetables; seafood; milk; and preserves, jams, jellies, pickles, and sauces. The general principles of commercial and home canning are the same, but the factory more accurately controls procedures and has highly specialized machinery. The Mason jar, popular in home canning, was patented in 1858. Home canning grew in popularity during World War II, when the harvest of "victory gardens" was canned. Canning leads to a loss of nutrient value in foods, particularly of the water-soluble vitamins. The home-canning methods recommended today are much more specific than the old-fashioned methods, which are no longer considered safe.
See A. C. Hersom and E. D. Hulland, Canned Foods (1981); C. Walker, The Complete Book of Canning (1982).
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