With warmth, water, and food all living things flourish and grow; most organisms require air, but some of the microorganisms do not. Where these conditions are best met, the organism is most active and multiplies most rapidly. To retard growth or to destroy life, the conditions must be the reverse of favorable. While warmth, say a temperature from 70° to 90° F., promotes the life of most microorganisms, intense heat destroys it. The boiling temperature, 212° F., will kill these lower organisms, although this heat has to be continued for some length of time, particularly in the case of spores. The spores of certain bacteria are quite resistant. A temperature of 32° F. and lower retards growth, but it requires extreme cold to destroy bacteria. Since moisture is necessary to all the lower organisms, they do not develop in a dry material or dry place.
We cannot destroy these lower forms of life by removing food from them, since they are ever present, but we can make the food unavailable to them through the introduction in the material of certain substances called preservatives which prevent their growth. The preservatives long familiar are salt, sugar, wood-smoke, spices, vinegar, and alcohol. While a small amount of sugar is necessary in the fermentation process, a large amount acts as a preservative, as in candied fruit. It is an interesting fact that alcohol and vinegar, products of fermentation processes, tend (when sufficiently concentrated) to stop the growth of the fermentation organisms.
To the reader who desires a fuller account of the bacteria, yeast, and molds, especially as related to household affairs, Buchanan's "Household Bacteriology" is recommended as the most recent and satisfactory book in this field.
When canned goods are put up in large quantities at the factory, abuses are likely to exist. Poor, even decayed, fruit may be used, the whole process may be unclean from beginning to end, and undesirable preservatives or an excess of sugar or spice may be introduced to cover the use of poor materials or methods. The condition of the worker in the cannery is one of the important industrial problems at the present time. Unhappily, poor conditions do often exist in canneries that turn out a cheap product. On the other hand, there are firms that may well take pride in their system from beginning to end.
All canned food should be exposed to the air for a short time before serving, and stirred that the material may be aerated. This partially removes a certain flatness of taste. Canned fruit is improved by reheating, even.
When possible, vegetables bought in a tin can should be washed in the colander before they are heated. This greatly improves the flavor.