Canning Reminders

Removing air bubbles and measuring headspace on jars of tomatoes before canning.

Removing air bubbles and measuring headspace on jars of tomatoes before canning. 
Rebecca Baxley, ©2019, Clemson Extension

  • Remember that vegetables, meat, fish, and poultry (low-acid foods) should be pressure canned for safety. Fermented vegetables and fruits (acid foods) can be canned in a boiling water bath. Note: Figs and tomatoes should be acidified.
  • Always start with a tested recipe before canning. Tested recipes can be found in the So Easy to Preserve book. For reliable resources, see HGIC 3001, Finding Reliable Recipes for Safe Food Preservation.
  • If no tested canning recipe exists for a product, freeze it for extended storage!!! Another option is to dry it.
  • If low-acid foods are being combined with high-acid foods, pressure canning is the correct and safe method to can. For example, pressure canning is required when combining ingredients such as lima beans and corn (both low-acid foods) with tomatoes (which, when canned by themselves, can be acidified and canned using a boiling water bath process). Use the process for the vegetable that requires the longest pressure canning time.
  • Remember that tested canning recipes are developed for altitudes of 0 to 1,000 feet. Adjust canning processes for altitudes above 1000 feet by following the recommendations in So Easy to Preserve or other reliable resources.
  • Jam and jelly recipes should never be doubled. Always make jelly or jam in quantities stated in the recipe. Doubling or tripling a recipe increases the boiling time of the fruit juice, resulting in loss of flavor and darkening and toughening of the product. Longer boiling also adversely affects pectin’s ability to form a gel.
  • A deep pressure canner can be used as a boiling water bath canner.  Just be sure there is enough space above the jars to allow for them to be covered by 1 inch of briskly boiling water.  Place the lid loosely on the canner – don’t fasten it. Leave the vent wide open so that steam escapes and pressure does not build up inside.  (Source: So Easy to Preserve)
  • Keep in mind that if the boiling water process time for a recipe is less than 10 minutes, jars need to be sterilized. (Boil jars for 10 minutes to sterilize. Keep jars hot.) Check the tested recipe for the correct processing time.
  • One of the most important things canners and cooks can do to prevent the spread of germs is to wash their hands. The kitchen is no exception!  Wash hands often under hot water with lots of suds for ~20 seconds when handling food.

If this document didn’t answer your questions, please contact HGIC at or 1-888-656-9988.

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