_by Carole Davis_[7]
Canning in the home is increasing in popularity as a method of food
preservation. Economic considerations are causing consumers to look for
ways to stretch their food dollars. By having their own gardens and
canning the harvested produce, they often can save money. Eating quality
of home-canned products encourages some individuals to can. The activity
of growing or obtaining produce and preserving it in the home sometimes
gives people a sense of personal achievement and satisfaction.
In canning, food is preserved by applying heat to prepared food in
containers so that micro-organisms that cause spoilage or food poisoning
are destroyed and enzymes that cause undesirable quality changes in the
flavor, color, and texture of food are inactivated. Preservation of food
by canning also depends on sealing the food in sterile, airtight
containers to prevent it from coming in contact with micro-organisms in
the environment.
Canning is not a difficult technique, but it must be done properly to
avoid spoilage and food poisoning, such as the often fatal botulism. It
is extremely important that only tested reliable instructions are used,
such as those found in U.S. Department of Agriculture publications.
Based on scientific research, specific instructions have been developed
for preparing, packing, and processing each food. Instructions should be
followed exactly from beginning to end--without taking any shortcuts or
altering any recipes.
Acidity of the food is the chief factor in influencing the time and
temperatures necessary for processing. The more acid the products, the
easier spoilage organisms are destroyed by heat. Acid foods--such as
tomatoes, fruits, and pickled vegetables--can be safely processed at the
temperature of boiling water in a boiling-water-bath canner. If spoilage
organisms are not killed by adequate processing, they will continue to
grow and could reduce the acid in the canned product, thus encouraging
the growth of more dangerous organisms, such as _Clostridium botulinum_.
Low-acid foods--all vegetables, except for tomatoes--require a more
severe heat treatment than acid foods to kill the organisms. The only
safe way to can these foods is with a steam-pressure canner, one with a
weighted or dial gage, to obtain temperatures above boiling.
_Clostridium botulinum_ is extremely dangerous in these low-acid foods
because if it is present, and the heat treatment has been insufficient,
it can grow and produce a deadly toxin in the sealed containers.
Processing times are based on sea level conditions where water boils at
212° F or, when under 10 pounds of pressure, at 240°. As the altitude
increases, the temperature at which water boils decreases. Therefore, at
altitudes above sea level you need to make adjustments in canning
instructions to insure that foods are adequately processed.
When using a boiling-water-bath canner you must add more time in
processing, as given in the table.
At altitudes above sea level it takes more than 10 pounds of pressure
for the temperature of boiling water to reach 240° F.
When using the steam-pressure canner, the pressure must be increased
although the time remains the same as that recommended for sea level. At
altitudes above 2,000 feet, process as follows: