_by Frances Reasonover_[4]
Canning is probably the most economical and practical method of
preserving food at home. Among other things it is a way to save food
that otherwise might be wasted.
Cost of home canning depends on the kinds and sources of food canned as
well as the processing methods, containers, and equipment used. Other
cost factors--labor, energy, water and added ingredients--make exact
cost figures impossible to apply generally, but studies are reporting
averages that show canning to be economical.
The wise homemaker will can only the amount to be used within a year.
Food held longer will be safe to eat if it has a good seal and no signs
of spoilage, but there may be nutrient or quality loss, especially if
stored at temperatures above 70° F.
As a beginner canner you need to know something about micro-organisms,
including yeasts, molds and bacteria, on the food, in water, air and
soil, as causes of spoilage in foods. Knowing about these minute forms
of life, which are so abundant everywhere, will help make the work safer
as well as more interesting.
In addition to the action of these minute organisms, the spoiling of
fruits and vegetables is hastened by natural changes in color, flavor
and texture of the food. These changes result from the action of enzymes
or micro-organisms found in nature which break down and decompose
foodstuffs.
Bacteria are the most serious foes to combat in canning because they are
more difficult to kill by heat than either molds or yeasts.
Acid in canned food is expressed as pH value. Foods having a pH of 4.5
or lower are called high-acid foods and those with a value of 4.6 or
higher are termed low-acid foods.
Since few bacteria thrive in acids, their destruction is less difficult
in fruits than in vegetables (with the exception of tomatoes).
Botulism is a deadly poison caused by a toxin from the growth of spores
(seeds) of the bacteria, _Clostridium botulinum_. These spores will
produce a deadly toxin in low-acid foods in the absence of air (oxygen)
inside a sealed jar. Therefore, the spores must be destroyed by
processing under pressure at 240° F. The length of time has been
determined by scientists for each individual food.
_Clostridium botulinum_ will not grow in foods with a pH of 4.5 or
lower, so high-acid foods may be processed safely in boiling water at
212° F.