Among such foods are meat, fish, peas, corn,
beans, and meat soups. On the other hand, some foods contain acids that
prevent the growth of bacteria, and these keep easily. Among these are
rhubarb, cranberries, and green gooseberries. However, foods that keep
easily are few, and in most cases extreme care in the process of canning
must be exercised.
12. While warmth is necessary for bacterial growth, very high
temperatures will destroy or retard it. In canning, a temperature as
high as 212 degrees Fahrenheit, or boiling point, retards the growth of
active bacteria, but retarding their growth is not sufficient. They must
be rendered inactive. To do this requires either a higher temperature
than boiling point or long continued cooking at 212 degrees. _Spores_
are a protective form that many kinds of bacteria assume under
unfavorable conditions. They are very difficult to kill, and unless they
are completely destroyed in the canning process, they will develop into
active bacteria when conditions again become favorable. The result of
the spore development is the spoiling of the food.
13. Other things besides the application of heat assist in the keeping
of canned food, as, for example, the acids of the fruits and vegetables
themselves, as has been mentioned.
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