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Ensuring Safe Canned Foods (Part 1 Of 2)

Category: Misc

Author: The Savvybearcat

Date: 1/1/2007

Rating:

(3.0) by 1 users

Ingredients:

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Instructions:

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.

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