Do’s and Don’ts of Canning

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Our Virtual Food Preservation Series is officially underway. Our three classes offer different canning techniques such as water-bath canning, when you need to pressure can, and how to can fermented and pickled foods. To go along with our series, I wanted to offer a list of ‘Do’s and Don’ts’ when preserving foods. This information came from The University of Georgia’s Cooperative Extension and their resource called “So Easy to Preserve.”

  1. Can food be re-canned if the lid does not seal?

Canned food can safely be recanned if the unsealed jar is discovered within 24 hours. To re-can, remove the lid and check the jar sealing surface for tiny nicks. Change the jar; if necessary, add a new treated lid and reprocess using the same processing time.

  1. If my recipe doesn’t call for processing, do I need to do so?

Many recipes passed down through the years or found in older cookbooks do not include instructions for processing. The foods are usually canned by the open kettle method, sealed and stored. Foods prepared in this manner present a serious health risk – particularly low acid foods. To minimize the risk of food spoilage, all high acid foods should be processed in a water bath canner or pressure canner and all low acid foods in a pressure canner.

  1. Do I really need to leave a certain amount of headspace in the jar?

Yes, leaving the specified amount of headspace in a jar is important to assure a vacuum seal. If too little headspace is allowed the food may expand and bubble out when air is being forced out from under the lid during processing. The bubbling food may leave a deposit on the rim of the jar or the seal of the lid and prevent the jar from sealing properly. If too much headspace is allowed, the food at the top is likely to discolor. Also, the jar may not seal properly because there will not be enough processing time to drive all the air out of the jar.

  1. How long will canned food keep?

Properly canned food stored in a cool, dry place will retain optimum eating quality for at least 1 year. Canned food stored in a warm place near hot pipes, a range, a furnace, or in indirect sunlight may lose some of its eating quality in a few weeks or months, depending on the temperature. Dampness may corrode cans or metal lids and cause leakage so the food will spoil.

  1. Is it necessary to sterilize jars before canning?

Jars do not need to be sterilized before canning if they will be filled with food and processed in a boiling water bath canner for 10 minutes or more or if they will be processed in a pressure canner. Jars that will be processed in a boiling water bath canner for less than 10 minutes, once filled, need to be sterilized first by boiling them in hot water for 10 minutes before they’re filled.

  1. Can two layers of jars be processed in a canner at one time?

Yes, in either the boiling water bath or pressure canner. Place a small wire rack between the layers so water or steam will circulate around each jar. Make certain that the water covers the tops of all jars by 1 inch in a boiling water bath canner. The pressure canner should have 2 to 3 inches of water in the bottom.

  1. Is it necessary to exhaust a pressure canner?

Yes, it is very important to allow steam to escape for 10 minutes before closing the valve, or placing the weight on the vent. If the canner is not exhausted, the inside-temperature may not correspond to the pressure on the gauge.

  1. Is it safe to can green beans in a boiling water bath if vinegar is used?

No. Recommended processing methods must be used to assure safety. Recommended processing times cannot be shortened if vinegar is used in canning fresh vegetables (this does not refer to pickled vegetables). Green beans should be canned in a pressure canner.

  1. What vegetables expand instead of shrink during processing?

Corn, peas and lima beans are starchy and expand during processing. They should be packed loosely.

  1. Can I can my own salsa recipe?

Salsas are usually mixtures of acid and low-acid ingredients; they are an example of an acidified food. The specific recipe, and sometime preparation method, will determine if a salsa can be processed in a boiling water canner of a pressure canner. A process must be scientifically determined for each recipe. Your county Extension agent will have tested recipes for salsas.

  1. How do I can oil with herbs? Can I can pesto?

Herbs and oils are both low-acid and together could support the growth of disease-causing Clostridium Botulinum bacteria. Oils may be flavored with herbs if they are made up for fresh use, stored in the refrigerator and used within 2 to 3 days. There are no canning recommendations. Fresh herbs must be washed well and dried completely before storing in the oil. The very best sanitation and personal hygiene practices must be used. Pesto is an uncooked seasoned mixture of herbs, usually including fresh basil, and some oil. It may be frozen for long term storage; there are no home canning recommendations.

You still have time to sign-up for some of our virtual food preservation workshops! Visit to read about and sign-up for our upcoming workshops.