Canning is the process in which foods are placed in jars or cans and heated to a temperature that destroys microorganisms and inactivates enzymes. This heating and later cooling forms a vacuum seal. The vacuum seal prevents other microorganisms from recontaminating the food within the jar or can. High acid foods such as fruits and tomatoes can be processed or "canned" in boiling water, while low acid vegetables and meats must be processed in a pressure canner at 240 degrees Fahrenheit (10 pounds pressure at sea level).

Jams and jellies have a very high sugar content. The sugar binds with the liquid present making it difficult for microorganisms to grow. To prevent surface contamination after the product is made and thus possible yeast or mold growth, these are either canned, frozen or refrigerated.

A pressure cooker cooks foods (with some added liquid) in a tightly sealed pot at a temperature higher than the standard boiling point. When the cooker is set over high heat, steam pressure builds and the internal temperature rises, increasing the boiling point from the standard 212 degrees to 254 degrees Fahrenheit. Under high pressure, the fiber in food is tenderized and flavors mingle in record time. As a result, the cooking time is usually reduced by 2/3.

The DUROMATIC pressure cooker is the highest quality stainless steel pressure cooker on the world market. It features an automatic lid locking system and a spring-loaded stationary safety valve. When the first red ring appears on the valve, the internal pressure has been raised to 8 pounds per square inch above the external pressure (235 degrees Fahrenheit); when the second red ring on the valve appears, the internal pressure has been raised to 15 pounds per square inch above the external pressure (254 degrees Fahrenheit).

A pressure canner is a specially made heavy pot that has a lid that can be closed steam tight. The lid is fitted with a vent (or petcock), a dial or weighted pressure gauge and a safety fuse. Newer models have an extra coverlock as an added precaution. It may or may not have a gasket. The pressure canner also has a rack to keep jars from bumping into each other causing possible breakage. Because each type of canner is different, be sure to read the directions for operating your canner. Kuhn Rikon does not manufacture a pressure canner.

The following are recommended Web sites for additional information on canning and preserving:

• The National Food Safety Database
• NDSU Extension Service - FAQs on canning

RECOMMENDED BOOKS ON PRESERVING:

• Putting Food By
  by Ruth Hertzberg, Janet Greene and Beatrice Vaughan
• So Easy To Preserve, Bulletin 989
  by Cooperative Extension Service
  The University of Georgia, College of Agricultural and Environmental Sciences
  Athens
  Call (706) 542-8999 to order.