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Canning FAQs

Q. Does altitude affect canning?

A. Yes, it does. Here are the guidelines for making Altitude Adjustments. View the Altitude Chart for Wyoming Communities.

  • Water bath canning:
    • If recipe calls for 20 minutes or less processing, increase the processing time by 1 minute for each 1,000 ft above sea level
    • If recipe calls for greater than 20 minutes processing, increase the processing time by 2 minutes for each 1,000 feet above sea level
  • Pressure canning:
    • At sea level use 10 psi
    • Increase psi by 1/2 lb for every 1,000 feet above sea level
    • If using a weighted gauge canner use the 15 lb. weight for all altitudes above 1,000 feet

Q. What is wrong with the open kettle method?
A. In this method, food is cooked in an ordinary kettle, then packed into hot jars and sealed without processing. Temperatures in open kettle canning may not be high enough to destroy spoilage organisms that may be in food. Spoilage bacteria may also enter the food while being transferred from kettle to jar. This method is not recommended.


Q. Is steam canning as effective as water bath canning?

A. Research shows that steam canners do not heat as evenly as water bath canning and thus do not heat to as high of a temperature. This results in less bacteria being killed in the processing. The use of steam canners for home canning is not recommended.


Q. If the jar seals, am I assured the food will be safe to eat?

A. No. It takes a lot less heat to seal the lid than to properly process the contents of the jar. If you followed directions correctly, you can be sure the food will keep and be safe to eat. That is why it is very important to select the correct method and carefully follow directions.


Q. Why is it necessary to process jellies, conserves, preserves, and marmalades?

A. Mold and other spoilage microorganisms can grow if the jar is not properly processed and sealed tightly to exclude air. Water bath processing produces a strong vacuum seal.

Q. Can low-acid food be reprocessed if it was incorrectly processed or if lids failed to seal?
A. If less than 24 hours have gone by since the food was processed, do one of the following:

  1. Refrigerate the food and use it in the next day or two.
  2. Freeze the food. Drain vegetables before freezing.
  3. Reprocess the food. Use the same jars (check jar rim and headspace) or put in a clean hot jar. Use new lids and process again for the full time. The quality of twice-processed food will be poor.


Q. How long may canned foods be stored?

A. The recommended storage time for home-canned foods is one year. However, a period of two to three years is considered a reasonable storage time. With longer storage, the eating quality and nutrient content of the food will drop.


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Issued in furtherance of extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kelly Crane, Director, University of Wyoming Extension, College of Agriculture and Natural Resources, University of Wyoming Extension, University of Wyoming, Laramie, Wyoming 82071.

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