What Does pH Have to Do With Canning Foods?

Pamela Schmtz,
Home & Garden Information Center

The acidity or pH of a food is critical to determining the right and safe way to can foods. You do not need to know the actual pH of a food, but you must use a tested canning recipe based on the pH value of a food and other factors. Acid foods such as fruits and pickles with a pH of 4.6 or lower may be canned in a water bath canner. Low-acid foods such as vegetables and meats with a pH above 4.6 must be processed in a pressure canner. Clostridium botulinum bacteria are the main reason why low-acid foods must be pressure canned to be safe. Clostridium botulinum spores can survive boiling water temperature (212 °F) and grow in a sealed jar of low-acid food. The spores can change into the vegetative cells that produce the deadly botulinum toxin. You must use a pressure canner to raise the temperature to the desired 240–250 °F to destroy the spores during the canning of low-acid foods. Some foods, such as figs and tomatoes, may be processed as acid foods, but because they may have pH values slightly above 4.6, lemon juice or citric acid must be added before canning.

For more information see HGIC 3030, Canning Foods—the pH Factor.

Page maintained by: Home & Garden Information Center

This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.