*  Exported from  MasterCook  *
                  ENSURING SAFE CANNED FOODS (PART 1 OF 2)
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 Serving Size  : 1    Preparation Time :0:00
 Categories    : Canning                          Information
   Amount  Measure       Ingredient -- Preparation Method
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   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.
   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
   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.
   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
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