Methods for canning foods at home have changed greatly since the procedure was first introduced almost two centuries ago. Since then, research has enabled home canners to simplify and safely preserve higher quality foods. Knowing why canning works and what causes food to spoil underscores the importance of following directions carefully.
How Canning Preserves Foods
Invisible microorganisms are all around us. Many are beneficial; others are harmful. All foods contain microorganisms, the major cause of food spoilage. Proper canning techniques stop this spoilage by using heat to destroy microorganisms. During the canning process, air is driven from the jar and a vacuum is formed as the jar cools and seals, preventing microorganisms from entering and recontaminating the food. It does not take long at 212 degrees Fahrenheit (F), the temperature at which water boils, to force air out, create a vacuum, and seal a jar. It does, however, take a specific amount of heat for a specific amount of time to kill certain bacteria. Although a jar is “sealed,” all bacteria are not necessarily killed. Adequate acid (as in pickled products and fruits) or sugar (as in jams and jellies) protects against the growth of some microorganisms. In low-acid foods, however, some microorganisms are not destroyed at 212 degrees F. Low-acid foods, therefore, must be heated to higher temperatures that can be reached only with a pressure canner. Low-acid foods, such as vegetables, meat, poultry, and fish, must be pressure canned at the recommended time and temperature to destroy Clostridium botulinum, the bacterium that causes botulism food poisoning. Canning low-acid foods in boiling water canners is absolutely unsafe
To read the full article on Canning Basics, including step by step instructions, click here.
Information compiled by Ruth Anne Foote, Extension Agent, Home Economics, Mercer County.
Updated by Marcia Jess, Extension Educator, Family and Consumer Sciences, Ottawa County.
Reviewed by Dan Remley, Extension Educator, Family and Consumer Sciences/Community Development, Butler County.