The United States Department of Agriculture recommends the pressure cooker as being the only safe method for canning low acid foods; vegetables, meat and poultry.
There are invisible micro-organisms present all around us. Fruits, vegetables and meat contain these micro-organisms 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 basics agents of food spoilage; enzymes, mold, yeast and bacteria. Canning disrupts the natural spoiling process so the food can be preserved safely. Molds, yeast and enzymes are destroyed at temperatures below 212 degrees Fahrenheit; the temperature at which water boils (except in mountainous regions). Therefore the boiling water process is sufficient to destroy those agents.
Bacteria however, are not as easily destroyed. The bacteria, clostridium botulinium, produces a spore that makes a poisonous toxin which causes botulism. The spore is not destroyed at 212 degrees Fahrenheit. In addition, the bacteria thrives on low acid foods in the absent of air. For a safe food product, low acid foods need to be processed at 240 degrees, which can be achieved only with a pressure cooker.
In pressure canning, some of the water in the pressure cooker is converted to steam, which creates pressure within the cooker. As pressure increases, temperatures increases; 5 pound increments at 228 degrees Fahrenheit, 10 pounds pressure at 240 degrees Fahrenheit and 15 pounds of pressure at 250 degrees Fahrenheit. This pressurized heat destroys the potentially harmful spores. As the jars cool, a vacuum is formed, sealing the food within and preventing any new micro-organisms 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 ten minutes at altitudes below a thousand feet. Extend the boiling time 1 minute for each thousand-foot increase in altitude.
Many times odors that cannot be detected in the cold 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 half pints, pints and quarts; with threads on the cap which may be screwed on. See the owners manual of your pressure cooker for the correct size of mason jars to be used.
Closure of Mason Jars: The two-piece vacuum cap consist of a flat metal lid held in place by a screw band. A rubber compound on the underside of the lid forms a seal during the process. Follow the closure process of the manufacturer to be certain there is a good seal. If the closure has not sealed, completely reprocess or use the food immediately. Refer to the closure directions for additional information.
Maximum Jar Capacity: An example of a 16 quart pressure cooker and it's equivalent jar capacity.
- 12 half-pint jars
- 10 pint jars
- 7 quart jars
