If pressure canning seems intimidating to you, take some time to learn about the process and how it can be a safe method for preserving food at home.
Still learning about canning? Please visit this page to learn about the various canning equipment and how the process works.
What is pressure canning?
A pressure canner is a specialized piece of equipment that can reach in excess of 240ºF inside. That temperature cannot be achieved in a simple boiling water bath; water boils at 212ºF which is not hot enough to kill botulism spores.
Canners like this have a lock-on lid that retains steam when heated. As part of the process, all air is pushed out of the canner and steam is trapped inside. This causes pressure to build, allowing the temperature in the pressure canner to rise above normal boiling point.
Why is this important? Pressure canning is the only safe way to make low acid foods shelf stable.
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What are low acid foods?
Food items that have a pH above 4.6 are classified as low acid foods. These include beans, meats, seafood, broth, and most garden vegetables. Figs, banana, and papaya are fruits that fall into the low acid category.
Tomatoes are right on the line and can be pressure canned or acidified to create a safe product for water bath canning.
These low acid foods have the potential to harbor a dangerous bacterium called clostridium botulinum, so they need to be processed with that in mind.
A temperature high enough to kill toxic spores can only be achieved with a pressure canner operated at 10.5 psi at sea level.
If you live at higher elevations, you will need to adjust accordingly. See chart below for recommended adjustments based on your altitude.
It’s important to note that it’s not the pressure that kills bacteria. It’s the heat. And as already mentioned, that kind of heat can only be achieved under pressure.
Pressure canner safety
While this may all sound like a bit much, modern day pressure canners are much safer than your grandma’s canner. Be sure to follow the manufacturer’s directions, though.
I use an All American canner. Its lid is locked in place, tightened down with strong wing nuts. If excessive pressure ever built up, steam would dislodge the weight and dissipate through the vent pipe.
Carefully watching the pressure gauge and monitoring the heat while processing will prevent excessive steam from building up.
Maintaining your equipment
A pressure canner is different than a regular cooking pot and needs extra care. Dial gauge canners need to be calibrated annually for safety. Contact your local cooperative extension office or the manufacturer to find out where you can have this done.
Avoid immersing the lids of dial gauge canners in water, as water can get into the gauge and cause damage.
Processing jars for food preservation
You’ll fill and seal jars for pressure canning much the same way you would for water bath canning. The difference is that you’ll need a bigger headspace between the product and the jar rim.
Transfer full jars to the canner and process according to recipe instructions.
Follow the full step-by-step instructions below.
- Ingredients for making the recipe of choice
- Pressure canner
- Canning jars, lids, and rings
- Jar lifter
Take the time to read the manufacturer’s guidelines before beginning. There will be some variations between manufacturers so you need to understand your particular model.
Preparing the product
- Wash and rinse jars and rings in hot water. Inspect each jar for chips on the rim, which can impair sealing. Set jars upside down on a clean towel or keep warm in the oven.
- Follow manufacturer’s instructions for preparing lids. If instructions are not available, heat a pot of water to 180ºF and drop flat lids into the hot water; remove from heat. Do not let the water get hotter than this, as this can damage the sealing compound.
- Pack the food according to the recipe. With pressure canning a one-inch headspace is pretty standard.
- Slip a plastic knife or tool between the jar and the contents of the jar to displace any bubbles. As bubbles are dispersed, the level of liquid may drop; add more to maintain the appropriate headspace.
- Wipe the rims and threads of the filled jars with a damp cloth to remove residue that may impair sealing.
- Set a flat lid on the jar and screw on a ring. Tighten the band firmly, but not so that it’s forced on.
Processing jars in a pressure canner
- Set the rack on the bottom of the pressure canner and add 2”-3” of water. Begin warming over medium heat with the lid off.
- Use canning tongs to set filled jars into the canner. You may stack the jars. Set a second rack on top of the first layer and add more jars, begin sure to stagger their location. Avoid overcrowding the jars.
- Following manufacturer’s instructions, lock the lid in place securely.
- If you’re using an All American canner (as I do) remember to add a thin layer of olive oil to the beveled edge of the rim where the cover touches. You can also (optionally) add some to the threads of each wing nut to keep them lubricated and easy to turn.
- Turn heat to high. Do not leave the pressure canner unattended while it’s heating or during the entire cooking process.
- Allow steam to escape from the vent for ten minutes. Air trapped inside the canner can lower the internal temperature of the canner and cause under processing.
- Set weight on the vent or close the petcock. (This will depend on your model.)
- For dial gauge canners: When the dial reaches the desired pressure, adjust the heat to hold it at that pressure. Begin timing (according to recipe) when the correct pressure is reached.
- For weighted gauge canners: Watch for the weight to begin jiggling or rocking when 10-15 pounds of pressure is achieved. Adjust the heat so that the gauge continues a slow and steady rocking motion. Begin timing when the correct pressure is reached.
- SEE CHART BELOW FOR ADJUSTING PROCESSING TIME FOR ALTITUDE
- Maintain steady pressure. This is critical. If the pressure drops below the recommended level, begin timing all over again. To avoid having to restart the timing, do not leave the area where you’re processing and check the pressure often.
- Once processing time is complete, turn off the heat. Don’t move the canner unless you absolutely must, as in the case of cooking over a coal or wood heated stove.
- Allow the pressure in the canner to drop to zero. Do not try to hurry the process. Once the gauge reaches zero, wait an additional 5 minutes.
- Lean the weight gently or slightly open the petcock. If pressure is audible or steam visible, let the weight remain in place or close the petcock as the pressure is not yet down far enough.
- Remove the cover of the canner, tilting it away from you to avoid burns.
- Use a jar lifter to carefully remove jars from the canner to a cooling rack or towel covered surface where there are no drafts.
- The jar’s contents may continue to boil once removed from the canner.
- Allow jars to sit undisturbed for several hours (ideally overnight) or until cool to touch. Remove the screw bands and check for a good seal. The lid should feel solid, be somewhat indented, and inflexible. Store any unsealed jars in the refrigerator and use quickly.
- Wash jars in soapy water to remove residue, rinse, dry, and label. Store without the screw on bands in a cool, dry, dark place.
Pressure Canner Instruction Manuals
When processing food in a pressure canner, follow the manufacturer’s instructions for your pressure canner. If you purchase a used pressure canner and didn’t get an instruction manual, one of these might help. Older owner’s manuals can sometimes be ordered from these companies as well.
Presto Pressure Canner Instruction Manuals
You can order older manuals from the Presto Company at no charge, through their online store. You will need to know the model number of your canner.
All American Pressure Canner Instruction Manual
Mirro Pressure Canner Instruction Manual
Granite Ware Pressure Canner Instruction Manual
Canning is an excellent way to preserve food for the pantry, but there are some important safety considerations to keep in mind.
- Know the difference between water bath canning and pressure canning. Low acid items must be pressure canned for safety.
- Altering ingredients may change the recipe’s pH, posing a safety issue. I highly recommend investing in pH paper to test your products for acidity level when canning.
- Use the proper jars and lids. Never reuse lids, with the exception of the Tattler lids that are intended for such a purpose.
- For more on canning equipment, please go here.
- The recipes on this site have been made following safe canning procedures by a certified Master Food Preserver.
Originally published February 2016; this post has been updated.