Over the years, I have seen pressure canner gauges that were spot on for accuracy. I have also seen some where the needle was stuck, or separate from the lid but reading 2 pounds, or tested 2, 3, 5 or even 8 pounds off. This summer I had the opportunity to spend time with people at a local farmers market, answering their questions and doing the annual pressure canner gauges testing. Some common questions came up so here they are with their answers.
Q: I have a weighted gauge canner. Do I need to have the gauge tested?
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 working order?
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. This is 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 make sure that the gauge on a canner is accurate or to know if it is off. 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 is old and worn enough so as to 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 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 – the 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 many of those 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 are welcome to contact me at 660-425-6434 or HackertJ@missouri.edu. My regular office hours are 8-4:30 Monday-Friday.
Since not everyone is available at those hours, I will be available at off-hours throughout the summer. Contact me by phone, email or other electronic communications on the second Tuesdays (July 9, Aug 13, Sept 10) 8-10 at night Saturdays (July 13, Aug 10, Sept 14) 9-11 in the morning, and second.
For more information on where the nearest University of Missouri Extension office is located, or for any other questions, contact me or check online at http://extension.missouri.edu/.
Janet M. Hackert
Regional Nutrition and Health Education Specialist
University of Missouri Extension