This article was written collaboratively by Lavonne Meyer and Jessica Becker.
Before the 1970’s pressure canners were heavy-walled kettles with clamp-on or turn-on lids. These pressure canners were fitted with a dial gauge, a vent pipe covered with a counterweight, and a safety fuse. Today, most pressure canners are light, thin-walled kettles with turn-on lids fitted with gaskets. The only canners that should be used are canners with the Underwriter’s Laboratory (UL) approval.
A high temperature for an extended period of time is what kills microorganisms, not pressure. Pressure canners allow temperatures to reach above boiling. For example, a pressure canner reading 10.5 lbs. of pressure will reach a temperature of 240° F.
Problems that may arise in pressure canners are:
- Lower temperatures at higher altitudes. At higher altitudes air becomes thinner allowing the boiling point to be lower. Lower boiling points will not destroy all of the microorganisms.
- Trapped air in the canner. To prevent this every pressure canner must be vented 10 minutes before processing.
When using a pressure canner it’s important to follow all of these steps:
- Put 2-3 inches of hot water into the canner. Place the jars in the canner and then fasten the lid. Turn on the heat to highest setting.
- The weight should be left off of the vent or the petcock opened. The steam should be allowed to flow out at the highest heat setting for 10 minutes. After 10 minutes place the weight or close the petcock. The canner will begin to pressurize in the next 3-10 minutes.
- Begin timing the process when the dial gauge reads the recommended pressure. When using a pressure canner without a dial gauge begin timing when gauge begins to jiggle.
- Regulate heat to maintain constant pressure.
- Allow canner to cool naturally after the correct amount of processing time. Cooling allows depressurizing.
- Once the canner is depressurized completely remove the weight or open the petcock. After 10 minutes has passed remove the lid and use a jar lifter to remove the jars.
- Let the jars cool for 12-24 hours, and then remove the ring bands.
- Clean pressure canner according to manufacturer’s instructions.
If pressure falls below recommended at any point during processing bring pressure back up and start the timing process again from the beginning. This ensures the safety of the product.
- Andress, E. Preserving Food: Using Pressure Canners. National Center for Home Food Preservation. University of Georgia Cooperative Extension, Accessed July 7, 2014.
- General Canning Information. National Center for Home Food Preservation. USDA, 2009. Accessed July 7, 2014.