New to Canning? Extension Can Help.

— Written By Ann Simmons and last updated by
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Canning involves placing food in jars and heating them to a temperature that is high enough to inactivate enzymes and destroy harmful pathogens that cause foodborne illness. When a jar of food is heated and cools, the result is a vacuum seal that prevents pathogens from entering the jar and contaminating the food. There are two methods of canning–one is the boiling water (water-bath) method, and the other is pressure canning.

The boiling water method is used for canning acid foods like fruit, tomatoes, pickles, jams and jellies. Due to the presence of acid, heating these products to boiling temperatures (at least 212°F) for a specified amount of time is sufficient. However, because of the risk of Clostridium botulinum, the bacteria that causes botulism, low-acid foods like green beans, corn, okra, and meats must be processed in a pressure canner.

When low-acid foods are improperly processed, Clostridium botulinum can grow in jars of canned foods and produce the botulinum toxin. Persons exposed to the botulinum toxin can experience nausea, blurred vision, dizziness, difficulty swallowing and speaking, paralysis and death. Destroying Clostridium botulinum requires heating foods to a temperature of at least 240°F, which is achieved in a pressure canner operated at the correct pressure and time for specific foods. For example, at altitudes up to 2000 feet above sea-level, processing green beans properly in a dial-gauge canner requires 11 pounds of pressure for 25 minutes.

There are some low-acid foods for which there are no approved or recommended canning processes. These include pumpkin puree, sweet potato puree and yellow squash. These foods cannot be processed safely in a pressure canner, but there are instructions available for freezing them.

You can contact a County Extension office if you have specific questions about canning. Extension Agents provide canning guidance from research-based resources. They want to you to learn how to can safely and understand the science behind the process.

You can also find research-based canning information at the National Center for Home Food Preservation website ( This site, maintained by the University of Georgia Cooperative Extension, is a highly-regarded, go-to resource used by Extension Agents for answering food preservation questions.

It is good to have a current research-based canning guide in your home cooking library. “So Easy to Preserve” published by the University of Georgia Cooperative Extension, “The USDA Complete Guide to Home Canning,” and the “Ball Blue Book” are all resources that can help you can food safely.

A pressure canner lid’s dial-gauge should be checked at least once a year to ensure that it works properly. Some Extension offices provide dial-gauge pressure canner lid testing by appointment or at community sites. The gasket should also be checked to ensure that the lid seals properly. After checking your gauge and gasket, the Agent will recommend repairs if needed.

If you have any questions about food preservation, please call the Catawba County Extension office at 828-465-8240. Be sure to check our website and monthly newsletter to see all of the great gardening and cooking classes, 4-H summer fun activities, farm tours, and local food events that are happening in Catawba County.