Homemakers Column: Frequently Asked Canning Questions

Christine J. Patrick, County Extension Agent – EFNEP

As a novice or experienced home canner, you may have questions about safely preserving and storing high-quality foods. The following list of answers to frequently asked questions can give you the skills and confidence to make your canning experience successful.

1. Can food be re-canned if the lid does not seal? Canned food be re-canned if the unsealed jar is discovered within 24 hours. Remove the cover and check the jar sealing surface for tiny nicks to re-can. Change the pot; if necessary, add a new treated lid and reprocess using the same processing time.
2. 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, sealed, and stored by the open kettle method. 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.
3. Do I need to leave a certain amount of headspace in the jar? Going the specified amount of headspace in a pot is essential to ensure a vacuum seal. If too little headspace is allowed, the food may expand and bubble out when air is forced out from under the lid during processing. The bubbling food may leave a deposit on the jar’s rim or the cover’s seal, preventing the pot from sealing correctly. If too much headspace is allowed, the food at the top will likely discolor. Also, the jar may not seal properly because there will not be enough processing time to drive all the air out of the pot.
4. How long will canned food keep? Properly canned food stored in a cool, dry place will retain optimum eating quality for at least one 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 that the food will spoil. As long as the seal remains intact, properly canned food will remain microbiologically safe indefinitely; however, eating quality will decline over time.
5.  Is it necessary to sterilize jars before canning? Pots do not need to be fixed 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. Once filled, jars that will be processed in a boiling water bath canner for less than 10 minutes must be sterilized first by boiling them in hot water for 10 minutes before they’re filled.
6.  Can two layers of jars be processed in a canner at one time? Yes, two layers can be processed at one time in either the boiling water bath or pressure canner. Place a small wire rack between the layers so water or steam will circulate in each jar. Make sure 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.
7. Is it necessary to exhaust a pressure canner? Yes, allowing steam to escape for 10 minutes is imperative 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 due to air in the canner.
8. Should liquid lost during processing be replaced? No, never replace liquid lost during processing. Loss of beverage does not cause food to spoil, though the food above the liquid may darken. If, however, the loss is excessive (for example, if at least half of the liquid is lost), refrigerate the jar(s) and use it within 2 to 3 days.
9. Is it all right to reuse jar fittings (lids and bands)? Covers should not be used a second time since the sealing compound becomes indented by the first use, preventing another airtight seal. Screw bands may be reused unless they are badly rusted, or the top edge is pried up, preventing a proper seal.
10. What causes jars to break in a canner? Breakage can occur for several reasons:
    1. Using commercial food jars rather than jars manufactured for home canning,
    2. Using pots that have hairline cracks,
    3. Putting jars directly on the bottom of the canner instead of on a rack,
    4. Placing hot food in cold jars, or
    5. I am putting jars of raw or unheated food directly into boiling water in the canner rather than into hot water (breakage occurs due to the sudden change in temperature-too wide a margin between the filled jars and water in the canner before processing).
11. If I find mold growing inside a jar of canned food, can I scrape it off and eat the food? Mold growth in foods can raise the pH of the food. In-home canned products, mold growth, could mean that the high acid products could become low acid and therefore run the risk of botulism or other bacterial spoilage. Thus, any home canned product showing mold growth should be discarded. USDA and microbiologists now recommend against even scooping out the mold on jams and jelly products and using the remaining jam or jelly, even though that used to be suggested. Sources: The National Center for Home Food Preservation “Frequently Asked Canning Questions” at https://nchfp.uga.edu

For more information, visit the Clemson Home and Garden Information Center website.

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