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( Frequently Asked Questions )


Most Frequently Asked Questions -- General

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

  2. If canned foods have been frozen during storage, are they safe to eat?
    Freezing does not cause food spoilage unless the seal is damaged or the jar is broken. This often happens as the food expands during freezing. However, frozen foods may be less palatable than properly stored canned food. In an unheated storage place, protect canned foods by wrapping the jars in paper or covering them with a blanket.

  3. 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.

  4. Do I really need to leave a certain amount of head space in the jar?
    Yes, leaving the specified amount of head space in a jar is important to assure a vacuum seal. If too little head space 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 head space 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.

  5. 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.

  6. 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 need to be sterilized by boiling them in hot water for 10 minutes before they're filled.

  7. Is it safe to process food in the oven?
    No. This can be dangerous because the temperature will vary according to the accuracy of oven regulators and circulation of heat. Dry heat is very slow in penetrating into jars of food. Also, jars explode easily in the oven.

  8. 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 around each jar. Make certain that the water covers the top of the jars by 1 inch in a boiling water bath canner. The pressure canner should have 2 to 3 inches of water in the bottom.

  9. 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.

  10. Should liquid lost during processing be replaced?
    No. Loss of liquid does not cause food to spoil, though the food above the liquid may darken.

  11. Is it all right to reuse jar fittings (lids and bands)?
    Lids 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 which would prevent a proper seal.

  12. Why is open kettle canning not recommended?
    In open kettle canning, food is cooked in an ordinary kettle, then packed into hot jars and sealed without processing. The temperatures obtained in open kettle canning are not high enough to destroy all spoilage and food poisoning organisms that may be in the food. Also, microorganisms can enter the food when it is transferred from the kettle to jar and cause spoilage.

  13. Why do the undersides of metal lids sometimes discolor?
    Natural compounds in some foods, particularly acids, corrode metal and make a dark deposit on the underside of jar lids. This deposit on lids of sealed, properly processed canned foods is harmless.

  14. 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 jars that have hairline cracks, 3. Putting jars directly on bottom of canner instead of on a rack, 4. Putting hot food in cold jars, or 5. Putting jars of raw or unheated food directly into boiling water in the canner, rather than into hot water (sudden change in temperature-too wide a margin between temperature of filled jars and water in canner before processing).

  15. If I find mold growing inside a jar of canned food, can I just scrape it off and eat the food?
    Mold growth in foods can alter the pH of the food. In home canned products, this 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 that shows signs of mold growth should be discarded. The exception to this is jellied products. In these the high sugar content would prevent the growth of Clostridium botulinum. In jellied products, remove any surface mold plus inch of the good product underneath and then use the rest immediately. Jellied products with extensive mold should be discarded.

  16. How can I remove scale or hard-water film from canning jars?
    Soak jars for several hours in a solution containing 1 cup of vinegar and 1 gallon of water.

    Vegetables and Fruits

  17. Is it safe to can food without salt?
    Yes. Salt is used for flavor only and is not necessary to prevent spoilage.

  18. Is it safe to can fruits without sugar?
    Yes. Sugar is added to improve flavor, help stabilize color, and retain the shape of the fruit. It is not added as a preservative.

  19. Can fruits and vegetables be canned without heating if aspirin is used?
    No. Aspirin should not be used in canning. It cannot be relied on to prevent spoilage or to give satisfactory products. Adequate heat treatment is the only safe procedure.

  20. 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).

  21. Should all vegetables be precooked before canning?
    For best quality, yes. However, some vegetables can be packed raw or cold into jars before being processed in the pressure canner.

  22. What vegetables expand instead of shrink during processing?
    Corn, peas and lima beans are starchy and expand during processing. They should be packed loosely.

  23. What causes corn to turn brown during processing?
    This occurs most often when too high a temperature is used causing caramelization of the sugar in the corn. It may also be caused by some minerals in the water used in canning.


  24. Should giblets of chicken be canned in the same jar with chicken?
    No. Their flavor may permeate other pieces of chicken in the jar.

  25. Is it safe to can meat and poultry without salt?
    Yes. Salt is used for flavor only and is not necessary for safe processing.

  26. Why is it necessary to remove as much fat from meats as possible before canning?
    Any fat that gets on the rim of the canning jar can prevent an airtight seal. Excess fat in jars makes it easier for the fat to climb the sides of the jar and contaminate the seal.


All information Courtesy the "University of Georgia - So easy to Preserve Guide ".

CanninAfrica compiled and maintained

 by Rosalie Acornley Webmaster.