Temperature is one determining
factor in the safety of home preserved foods.
Most bacteria, molds, and yeasts grow best at room temperature. As temperature is decreased, the activity of
bacteria is slowed down. As temperature is increased, an increasing
number of bacteria are killed.
Processing foods in a boiling water bath will
kill most bacteria, molds and yeasts. However,
in an attempt to survive under stressful conditions, some bacteria will produce
spores, a seed-like product, that can survive the temperature of boiling water. When temperature and growing conditions
improve, these spores can germinate producing a toxin. This is especially dangerous in the case of Clostridium botulinum which produces a
toxin that affects the central nervous system and may cause death. Besides its need for room temperature, Clostridium botulinum needs a low acid
environment in the absence of oxygen in order for its spores to produce this
deadly toxin. Canned vegetables and
meats provide that environment. That is
the reason for using a pressure canner to process low acid foods. Pressure will increase the temperature inside
a canner to above the boiling point of water.
Note
that the temperatures described below are based at sea level. As altitudes increase, it is necessary to
increase the length of processing time to process foods in a boiling water bath
and to increase the pounds pressure in a pressure canner. Below are important temperatures and temperature ranges to be aware of.
240ºF. — Bacterial spores are
destroyed in low-acid foods
240ºF. — Low acid foods processed
in pressure canner at or below 1,000 feet
212ºF. — Boiling point of
water. Processing temperature for high acid
foods in boiling-water bath at or below 1,000 feet
180-212ºF. — Temperature at which molds, yeasts, and some
bacteria are destroyed in acid foods
140-180ºF. — Growth of bacteria,
molds, and yeasts slowed, but may allow survival of some microorganisms
40-140ºF. — Active growing range
of molds, yeasts, and bacteria
50-70ºF. —Storage temperature for
home canned and dehydrated foods
32ºF. — Growth of some bacteria,
yeasts, and mold slowed
0 to -10°F. — Ideal freezer temperature
