Why is it necessary to use a pressure canner for certain types of food?
A. Canning destroys the enzymes, molds, yeasts, and bacteria that cause food spoilage. Most of these microorganisms are killed by processing food at boiling temperature (212°F) for a specified time period. The temperature and time required to destroy bacteria is determined in part by the acidity of the food being canned. Along with heat, the natural acid in fruits and tomatoes retards bacteria growth. Some bacteria, such as Clostridium botulinum, can be more difficult to destroy, so canning at a higher temperature is absolutely necessary. Low-acid foods (vegetables, meats, poultry, and seafood) must be canned at a temperature of 240°F or higher and held there for the time specified in the recipe in order to destroy the bacterial spores present in these foods. Pressure canning utilizes pressurized steam to reach this superheated temperature. Therefore, the United States Department of Agriculture recommends pressure canning as the only safe method of preserving low-acid foods. Low-acid f
