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PRessuRe CanninG
The United States Department of Agriculture recommends the
pressure canner as being the only safe method for canning low
acid foods—vegetables, meats, and poultry.
There are invisible microorganisms present all around us. Fruits,
vegetables, and meat contain these microorganisms naturally, and
yet, they are not a problem unless food is left to sit for extended
periods of time, causing food spoilage. This is nature’s way of
telling us when food is no longer fit to eat.
There are four basic agents of food spoilage—enzymes, mold,
yeast, and bacteria. Canning interrupts the natural spoilage cycle
so food can be preserved safely. Molds, yeast, and enzymes are
destroyed at temperatures below 212°F, the temperature at which
water boils (except in mountainous regions). Therefore, boiling
water processing is sufficient to destroy those agents.
Bacteria, however, are not as easily destroyed. The bacteria,
Clostridium botulinum produces a spore that makes a poisonous
toxin which causes botulism. This spore is not destroyed at 212°F.
In addition, the bacteria thrive on low acid foods in the absence of
air. For a safe food product, low acid foods need to be processed
at 240°F, which can be achieved only with a pressure canner.
In pressure canning, some of the water in the pressure canner is
converted to steam, which creates pressure within the canner. As
pressure increases, temperature increases, 5 pounds pressure—
228°F, 10 pounds pressure—240°F, 15 pounds pressure—250°F.
This pressurized heat destroys the potentially harmful bacterial
spores. As the jars cool, a vacuum is formed, sealing the food
within and preventing any new microorganisms from entering
and spoiling the food.
As a safeguard against using canned foods which may be affected
with spoilage that is not readily detected, boil all low acid foods
and tomatoes for 10 minutes at altitudes below 1,000 feet. Extend
the boiling time by 1 minute for each 1,000 foot increase in
altitude.
Many times odors that cannot be detected in the cold product will
become evident by this method. If, after boiling, food does not
smell or look right,
discard it without tasting .
MASON JARS:
While there are many styles and shapes of
glass jars on the market, only Mason jars are recommended for
home canning. Mason jars are available in ½ pint, pint, and quart
capacities with threads on which a cap may be screwed. See
the chart below for the jar capacity of your canner. Additional
information may be obtained from the manufacturers of Mason
jars.
CLOSURES FOR MASON JARS:
The two-piece vacuum cap
consists of a flat metal lid held in place with a screw band. A
rubber compound on the underside of the lid forms a seal during
processing. Follow the closure manufacturer’s directions for using
the two-piece cap and for testing for a proper seal. If the closure
has not sealed, completely reprocess or use the food immediately.
Refer to the closure manufacturer’s directions for additional
information.
MAxIMUM JAR CAPACITIES
(For Model Numbers beginning with 0175)
(For Model Numbers beginning with 0178)
Regular jars
Wide mouth jars
Regular jars
Wide mouth jars
12 half-pints
8 half-pints
24 half-pints
16 half-pints
10 pints
8 pints
20 pints
16 pints
7 quarts*
7 quarts*
7 quarts
7 quarts
*Do not use the boiling water method
with quart jars.
To achieve the maximum jar capacity
when pressure canning, it will be neces-
sary to double deck pint and ½ pint jars,
see page 42.
For boiling water method, do not double
deck jars.
