Canning basics

July 24, 2003

Canning must be done correctly to avoid contamination by bacteria, mold and yeasts, says Lynn F. Little, family and consumer sciences educator for the University of Maryland Cooperative Extension in Washington County.

Little, who writes a weekly column for The Herald-Mail, recommends the Penn State Food Safety Web site at and the National Center for Home Food Preservation's Web site at for the most up-to-date canning information. That site includes how-to guides for canning pickles and preserving many other foods.

There are two basic canning approaches: the boiling-water bath method for such higher-acid foods as preserves, pickles, tomatoes and most fruits; and the pressure method for low-acid foods, including most vegetables, meats and poultry that need to be processed above the boiling point to ensure killing bacteria that can cause deadly botulism or other food poisoning.

Steam pressure canners can be borrowed from the local extension service.

Some basic canning tips include:

  • Use the right containers. The U.S. Department of Agriculture recommends glass Mason-type threaded home-canning jars with self-sealing lids. The jars may be reused but must be washed and carefully rinsed before each use. New lids are required for each use.

  • Remove air bubbles by putting a flat, plastic spatula between the food and the jar, turning the jar and moving the spatula up and down.

  • Adjust the "headspace," the unfilled space above the food in the jar: 1/2 to 1 inch for vegetables; 1/4 to 1/2 inch for fruits.

  • Make sure the food is processed long enough at high enough temperatures. U.S. Department of Agriculture recommendations are available on the Penn State Food Safety Web site.

  • Cool canned jars for 12 to 24 hours. Place jars on racks or towels to protect counters.

  • Test the jar's seal by pressing the middle of the lid with your finger. If the lid springs up when you release your finger, the jar is not sealed.

  • Remove the metal rings when jars are cooled and safely sealed.

  • Wash off the lid and jar to remove any food residue. Rinse, dry, label and date.

  • Store your canned foods in a clean, cool, dark, dry place.
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