Canning basics: Always vent the canner prior to bringing it to pressure.
When pressure canning, it’s very important to vent the canner prior to bringing it to the proper pressure for the food/recipe you are processing. Always. Even if your pressure canner manual does not include instructions for venting, always vent the pressure canner for 10 minutes prior to closing the petcock or applying the weighted gauge/counterweight to the vent pipe to bring the canner to pressure.
Why is this step so important? During the pressure canning process, it’s actually the temperature that matters, not the pressure per se. Pressure is used to achieve the high temperatures needed to destroy Clostridium botulinum spores in low acid foods. Without proper processing, these spores can germinate and produce a toxin that causes botulism, a potentially fatal disease.
If air is trapped in the canner during processing, the temperature obtained at a given pressure can be lowered, resulting in underprocessing. Thus, to ensure food safety, pressure canners should be vented to release all air before being pressurized.
Briefly, here’s how to vent a pressure canner
Fill the canner and lock the lid in place. Leave the vent pipe uncovered or manually open the petcock. Heat the canner on high, and when a full funnel of steam continuously exits the vent or petcock, set a timer for 10 minutes. Make sure the canner continuously exhausts for the entire 10 minutes. Once the time is up, place the counterweight or weighted gauge on the vent pipe or close the petcock to begin pressurizing the canner. Continue with the pressure canning process, referring to your canner’s manual and a research-based recipe for specific processing requirements.
For further information, visit the National Center for Home Food Preservation (NCHFP) or contact your local Cooperative Extension office.
Brought to you by the UCCE Master Food Preservers of El Dorado County
Last updated July 2025