Food is canned by heating what goes into the container and then sealing the container to keep out air and microbes. It is then reheated after the can/jar is sealed. Like cooked food, canned food is subject to changes in appearance and nutritional content. Heating food often changes its color and texture (see Chapter 20). It also destroys some vitamin C. But canning effectively destroys a variety of pathogens, and it deactivates enzymes that might otherwise cause continued deterioration of the food.
A modern variation on canning is the sealed plastic or aluminum bag known as the retort pouch. Food sealed in the pouch is heated but for a shorter period than that required for canning. As a result, the pouch method does a better job of preserving flavor, appearance, and heat-sensitive vitamin C.
The sealed can or pouch also protects food from deterioration caused by light or air, so the seal must remain intact. When the seal is broken, air seeps into the can or pouch, spoiling the food.
The technique of canning food in glass containers was discovered (depending on your source) either in 1809 or 1810 by Nicholas Appert, a Frenchman who noted that if he sealed food in a container while it was heating, the food stayed edible longer — much longer—than fresh food. According to Harold McGee, author of On Food and Cooking: The Science and Lore of the Kitchen, a wonderful guide to food technology, a tin of 114-year-old canned meat once was eaten without making anyone sick. To be fair, I must note that nobody cried, "Oh, wow, this is good," either.
According to Joseph Nathan Kane's Famous First Facts (H. W. Wilson Company), the first food canned in tin — salmon, oysters, and lobsters — was introduced in 1819 by New Yorkers Ezra Daggett and Thomas Kensett. Four years later, Daggett and Kensett took out a patent to "preserve animal substances in tin." New York inventor J. Osterhoudt later patented the first can with a key opener on October 2, 1866. (For the most part, keys have been replaced by pull tabs.) The first beer in cans (from the Gottfried Krueger Brewing Company of Newark, New Jersey) went on sale on January 24, 1935, in Richmond, Virginia. Pop!
A more serious hazard associated with canned food is botulism, a potentially fatal form of food poisoning caused by the failure to heat the food to high-enough temperatures or for a long-enough time to kill all Clostridium botu-linum (or C. botulinum) bacteria. Canning is based on temperatures and times necessary to destroy C. bot spores. C. botulinum is an anaerobic (an = without; aerobic = air) organism that thrives in the absence of oxygen, a condition nicely fulfilled by a sealed can. Botulinum spores not destroyed by high heat during the canning process may produce a toxin that can kill by paralyzing your heart muscles and the muscles that enable you to breathe.
To avoid potentially hazardous canned food do not buy, store, or use any can that is
II Swollen, which indicates that bacteria are growing inside and producing gas
i Damaged, rusted, or deeply dented along the seam, because a break in the can permits air to enter and may promote the growth of organisms (other than botulinum)
Consumer alert: Never, never, never taste any food from a swollen or damaged can "just to see if it's all right." Remember: When in doubt, throw it out.
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