micro-organisms that cause fermentation, putrefaction, and molding. The
reasons for the spoiling of food are thoroughly discussed in _Essentials
of Cookery_, Part 2, and in that discussion canning is mentioned as one
of the means of preserving food or preventing it from spoiling. However,
when canning does not prove effective, it is because undesirable
bacteria are present in the food. Either they have not been destroyed by
the canning process or they have been allowed to enter before the jar
was closed, and have then developed to such an extent as to cause the
food to spoil. Odors, flavors, and gases result from the putrefaction,
fermentation, or molding caused by these bacteria, and these make the
foods offensive or harmful, or perhaps both.

11. PREVENTING CANNED FOODS FROM SPOILING.--From what has just been
said, it will be seen that the success of canning depends entirely on
destroying harmful micro-organisms that are present in the food and
preventing those present in the air from entering the jars in which the
food is placed.

Some foods are more difficult to keep than others, because bacteria act
on them more readily and the foods themselves contain nothing that
prevents their growth. 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