By Cassidy Hobbs Hall
Area Agent, Family and Consumer Sciences
Johnston County Cooperative Extension
This is the 5th in a series of 6 Food Preservation articles that will publish each Friday
Participants in my food programming activities often mention how they are terrified of anything device building pressure- both pressure cookers, like an InstantPot, as well as pressure canners. Everyone knows someone who had a terrible experience with a pressure canner (prior to safety features) which has instilled fear. I am incredibly accident-prone, yet I am confident in using a pressure canner. If you are interested in pressure canning and looking to purchase equipment, a pressure cooker and pressure canner are not the same. You may even hear people use the terms interchangeably, but be sure to read the box for yourself. You can cook in a pressure canner, but you can not home-can in a pressure cooker. You also can not use an InstantPot (a pressure cooker) to safely home-can foods.
Some generations may suggest you should home-can based on their practices, however, those practices may be outdated and often risky. You wouldn’t use medical technologies from 1920 to treat an illness knowing better data and science is available today. Likewise, we now know much more about safety of canning recommendations- or lack thereof. Foods that lack their own or added acidity must be pressure canned in order for the foods inside the jar to heat to 240 degrees. This significant temperature ensures that Clostridium botulinum pathogens are “deactivated” and will not result in the foodborne illness of Botulism which is often fatal. You can’t see, smell, or taste these pathogens which is why choosing the correct canner method is absolutely crucial.
An additional component of properly canning involves achieving a vacuum seal. You’ll see a recommendation for the proper amount of headspace per recipe. Headspace is the space in the jar between the top of the liquid or food and the lid. Having too little headspace results in contents being forced out of the jars during processing which may also prevent the jar from sealing. If there is too much headspace left, the processing time may not be long enough to fully drive out the oxygen. This would mean a vacuum seal has not been created, leaving oxygen in the jar for microorganisms to use, resulting in spoiled or discolored foods. Boiling lid pieces prior to use also results in seal failures.
Processing time is important to creating a safe and quality product. Prior to starting your processing time, you’ll need to “vent” the canner. This means allowing steam to build inside the canner and escape through the vent prior to adding on the petcock or weighted gauge, depending on the pressure canner. You’ll want to be sure there is a strong, steady stream of steam before adding your petcock or weighted gauge. This allows the pressure inside the canner to equalize for a quality product. Once your canner builds the proper pressure, begin your processing time. The length of time recommended to process each food depends on the density of food, packing liquid, and pH. Do not guess at the processing time if you can’t find one. Call the Johnston County Cooperative Extension office (919-989-5380) for help.
There are various pressure canner methods to indicating how much pressure has built inside. You may use a dial gauge or a weighted gauge. Dial gauges work well for people like myself who want exact measurements at all times. Weighted gauges have five, ten, and fifteen pound settings indicated by placement or the number of rings placed on the weight. Weighted gauges make a nice “jiggling” noise and work well for folks who may walk away from the canner and want the confirmation from the sound of the weights steadily moving. It is important to note that loss of pressure may happen at any time. If this is the case, you must start over. Loss of pressure results in underprocessed foods deeming them unsafe.
Once the processing time ends, turn off the heat and let the canner cool naturally. You may remove the canner from the burner if possible, but do not force cooling. Forced cooling results in lost liquid and seal failures. Forced cooling includes using cold water, opening the vent port, or removing a weighted gauge before the canner is fully depressurized. After the canner has depressurized, remove the weight or petcock and wait ten minutes. Pressure canners manufactured after 1970 have safety locks, so do not attempt to force the canner open. Follow recommendations to let jars cool on a towel 12-24 hours.
If you want to pressure can on a glass-top stove, call the manufacturer to confirm it is possible. If the manufacturer does not confirm, you run the risk of the glass cracking due to the combination of heat and weight from a loaded canner. If you are interested in food preservation workshops, please visit https://johnston.ces.ncsu.edu/2020/06/home-food-preservation-online-series/
May 15th Article: Gearing Up to Preserve Local Foods
May 22nd Article: Dos and Don’ts of Freezing Produce
May 29th Article: Handling & Freezing Meats, Eggs, & Dairy
June 5th Article: Water Bath Canning Explained