Food Safety Feature Articles
Pressure canning FAQ’s and expert advice
Janet Hackert, Nutrition and Health Education Specialist, Harrison County, University of Missouri Extension
After testing many pressure canner gauges over the years, I have seen some that were spot on for accuracy. I have also seen some where the needle was stuck; the gauge was separate from the lid yet still reading 2 pounds; and there are those that have tested 2, 3, 5 or even 8 pounds off. I recently attended a local farmers market to do the annual pressure canner gauges testing and to answer questions. Here are some of the common questions that came up.
Q: I have a weighted gauge canner. Do I need to have the gauge
A: No. The weight is calibrated and unless it chips or breaks, it stays accurate.
Q: What about my pressure gauge – how do I know if it is in good
A: Sometimes a gauge’s appearance can give an indication of how well it works, or doesn’t. If the needle is not on zero when the canner’s pressure is zero, it is very likely that the gauge is too inaccurate to safely can food. Or if the gauge only shows pressure in increments of 5 with no markings in between, it is next to impossible to accurately keep the pressure at 11 psi, the most commonly used pressure for canning. Gauges without the unit markings are often so old that, when tested, they are inaccurate anyway.
Q: So how do I know if it is accurate?
A: Accuracy can be determined by testing it against a calibrated gauge. University of Missouri Extension offices in the northwest region have a tester that takes only minutes to determine whether or not the gauge on a canner is accurate. If the pressure is within 2 psi, it is okay to adjust for the difference. If it is more than 2 psi off, it is too inaccurate to use. The spring in the gauge that makes the needle move can get old and worn enough that it will not give a consistent reading. It is moving away from accuracy and should be replaced to avoid improper and unsafe canning.
Q: I have used my canner for years and I never had a problem. So
what if it is off?
A: If the canner is not at the recommended pressure during processing, the food inside the jars will either be cooked too much and will be of poor quality, or the product will not be thoroughly safe before storing on the shelf. The microorganism most likely to contaminate canned produce is Clostridium Botulinum. This botulism-causing germ thrives in a sealed, airless environment at room temperature, so a canning jar would be a veritable breeding ground. And the potentially deadly bacteria colony could grow huge without being able to be seen, smelled or tasted.
Q: Where can I get my gauge tested?
A: Gauges should be tested annually for accuracy. This can be done at the University of Missouri Extension county offices across northwest Missouri and at many other Extension offices across the state.
These are just a few of the more common questions that come up. If you have any other questions about food preservation, you can contact your local University of Missouri Extension office or contact Janet Hackert directly at 660-425-6434 or HackertJ@missouri.edu.
Last update: Monday, July 28, 2014