Ensuring Safe Canned Foods(Part 1 Of 2)

* Exported from MasterCook *

ENSURING SAFE CANNED FOODS (PART 1 OF 2)

Recipe By :
Serving Size : 1 Preparation Time :0:00
Categories : Canning Information

Amount Measure Ingredient -- Preparation Method
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***** NONE *****

Growth of the bacterium Clostridium botulinum in
canned food may cause botulism--a deadly form of food
poisoning. These bacteria exist either as spores or as
vegetative cells. The spores, which are comparable to
plant seeds, can survive harmlessly in soil and water
for many years. When ideal conditions exist for
growth, the spores produce vegetative cells which
multiply rapidly and may produce a deadly toxin within
3 to 4 days of growth in an environment consisting of:

* a moist, low-acid food
* a temperature between 40 degrees F and 120 degrees F
* less than 2 percent oxygen

Botulinum spores are on most fresh food surfaces.
Because they grow only in the absence of air, they are
harmless on fresh foods.

Most bacteria, yeasts, and molds are difficult to
remove from food surfaces. Washing fresh food reduces
their numbers only slightly. Peeling root crops,
underground stem crops, and tomatoes reduces their
numbers greatly. Blanching also helps, but the vital
controls are the method of canning and making sure the
recommended research-based process times, found in
these guides, are used.

The processing times in these guides ensure
destruction of the largest expected number of
heat-resistant microorganisms in home-canned foods.
Properly sterilized canned food will be free of
spoilage if lids seal and jars are stored below 95
degrees F. Storing jars at 50 degrees F to 70 degrees
F enhances retention of quality.

FOOD ACIDITY AND PROCESSING METHODS

Whether food should be processed in a pressure canner
or boiling-water canner to control botulinum bacteria
depends on the acidity in the food. Acidity may be
natural, as in most fruits, or added, as in pickled
food. Low-acid canned foods contain too little acidity
to prevent the growth of these bacteria. Acid foods
contain enough acidity to block their growth, or
destroy them more rapidly when heated The term "pH" is
a measure of acidity; the lower its value, the more
acid the food. The acidity level in foods can be
increased by adding lemon juice, citric acid, or
vinegar.

Low-acid foods have pH values higher than 4.6. They
include red meats, seafood, poultry, milk, and all
fresh vegetables except for most tomatoes. Most
mixtures of low-acid and acid foods also have pH
values above 4.6 unless their recipes include enough
lemon juice, citric acid, or vinegar to make them acid
foods. Acid foods have a pH of 4.6 or lower. They
include fruits, pickles, sauerkraut, jams, jellies,
marmalades, and fruit butters.

Although tomatoes usually are considered an acid food,
some are now known to have pH values slightly above
4.6. Figs also have pH values slightly above 4.6.
Therefore, if they are to be canned as acid foods,
these products must be acidified to a pH of 4.6 or
lower with lemon juice or citric acid. Properly
acidified tomatoes and figs are acid foods and can be
safely processed in a boiling-water canner.

Botulinum spores are very hard to destroy at
boiling-water temperatures; the higher the canner
temperature, the more easily they are destroyed.
Therefore, all low-acid foods should be sterilized at
temperatures of 240 degrees to 250 degrees F,
attainable with pressure canners operated at 10 to 15
PSIG. PSIG means pounds per square inch of pressure as
measured by gauge. The more familiar "PSIG"
designation is used hereafter in this publication. At
temperatures of 240 degrees to 250 degrees F, the time
needed to destroy bacteria in low-acid canned food
ranges from 20 to 100 minutes. The exact time depends
on the kind of food being canned, the way it is packed
into jars, and the size of jars. The time needed to
safely process low-acid foods in a boiling-water
canner ranges from 7 to 11 hours; the time needed to
process acid foods in boiling water varies from 5 to
85 minutes.

PROCESS ADJUSTMENTS AT HIGH ALTITUDES

Using the process time for canning food at sea level
may result in spoilage if you live at altitudes of
1,000 feet or more (Plate 2). Water boils at lower
temperatures as altitude increases. Lower boiling
temperatures are less effective for killing bacteria.
Increasing the process time or canner pressure
compensates for lower boiling temperatures.

Therefore, when following canning directions in this
series, select the proper processing time or canner
pressure for the altitude where you live. If you do
not know the altitude, contact your local county
Extension agent. An alternative source of information
would be the local district conservationist with the
Soil Conservation Service.

ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ ÿ * USDA Agriculture Information Bulletin No. 539
(rev. 1994) * Meal-Master format courtesy of Karen
Mintzias



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