What Is a Pressure Canner? A Plain Explanation

If the word "pressure" makes this equipment sound a bit scary, you're in good company. Once you know what the pot is doing, and why, it's a lot less mysterious.

What does it do?

Water in an open pot stops getting hotter once it boils. A pressure canner locks steam in, and that lets the inside get well above boiling. The USDA is careful about why this matters: pressure doesn't kill germs, but high heat held long enough does.

So pressure is a means to an end. Heat does the work. That's why the method exists: the spores behind botulism are hard to kill at boiling temperature. Our botulism page explains.

The USDA names two things that can spoil the math. They explain much of what you do with a canner:

• Altitude. Temperatures inside a canner are lower at higher altitudes, so canners must run at higher pressure for your altitude range. Our altitude page explains and links to the official tables.
• Trapped air. Air left in the canner lowers the temperature at a given pressure and leads to under-heating. So the USDA says all types of pressure canners must have the air let out before they're pressurized.

What are the parts for?

The USDA describes today's home pressure canners as lightweight, thin-walled kettles, most with turn-on lids. You'll find these parts:

• Jar rack: holds jars off the bottom of the pot (Presto).
• Gasket or sealing ring: makes a pressure-tight seal between lid and pot (Presto). At least one style seals with the metal surfaces touching instead, says University of Georgia Extension.
• Dial or weighted gauge: shows the pressure. A weighted gauge also controls it (USDA, University of Georgia Extension).
• Vent pipe or vent port: lets air and steam out before pressurizing, and lets excess pressure out (USDA, Presto).
• Vent and cover lock: keeps the lid from opening while there is pressure inside (USDA, Presto).
• Safety fuse or overpressure plug: lets excess pressure out if the vent pipe clogs (USDA, Presto).

Our gauge comparison sorts out the two kinds of gauge. The USDA also says to use only canners with Underwriter's Laboratory (UL) approval. University of Georgia Extension adds that the mark may appear only in the manual. That is an electrical and product safety mark. It says nothing about food.

What makes it a pressure canner, not just a big pot?

Listings use the name loosely, so it helps to know the test. For USDA instructions, Penn State says a pot must do three things:

1. Hold at least four quart jars upright with the lid on.
2. Let air out while it comes up to pressure.
3. Have a dial or weighted gauge, so you can confirm it stays at the right pressure the whole time.

The National Center for Home Food Preservation (the US canning experts at the University of Georgia, "the National Center" from here on) explains why a small pot falls short even if it builds pressure. The heat from coming up to pressure and cooling down counts toward the total. Small cookers go through both too quickly. The canner vs. cooker page compares them.

Holding four quart jars is one condition among several. It doesn't prove the heat-up, hold and cool-down match the tested process. Temperature decides.

What do you use one for?

Low-acid foods have a pH above 4.6. They include red meat, seafood, chicken, milk and all fresh vegetables except most tomatoes. The USDA says they must be canned in a pressure canner. The CDC says pressure canning is the only recommended method, and a boiling water canner does not protect against botulism in these foods.

The steps come from your tested recipe and your machine's manual. We publish no times, pressures or water amounts. The tested recipes page shows where to find them. Your canner's manual speaks for your exact model. How to use a pressure canner gives the order of the steps.

Are plug-in machines the same?

No. The description above is of a stovetop pot, the type the National Center says its instructions were written for. Plug-in machines get lumped in with it, and they shouldn't.

• Plug-in canner made just for canning. It is an appliance sold for pressure canning jars of food, with its own heating element and automatic controls. It's not the same as an electric pressure cooker or an electric water bath canner. Neither the USDA nor the National Center certifies or approves any canner.
• Cooker-canner combo. Penn State says these can't be recommended because research on their safety is missing. It names no brand. Putting the NESCO NPC-9 in that group is our own reading. Are electric pressure canners safe reports who says what.
• Electric multi-cooker. The National Center does not support USDA canning instructions in them, even with canning buttons. The CDC says not to use them for canning low-acid food.

A statement about one of these doesn't carry over to the others. Our guide to machine types puts them side by side.

What about an old canner?

The USDA says canners made before the 1970s were heavy-walled kettles with clamp-on or turn-on lids. University of Georgia Extension says old or possibly unsafe canners should not be used. It says to make sure an old pot really is a pressure canner and not an old sterilizer or steamer, and to inspect all parts first.

Where to go from here

Our stovetop canner guide compares the options. This is the pot we'd start with:

Our pick for stovetopAd

Presto

Presto 23-Quart Stovetop (01781)

A pot for your stove, the kind the USDA's canning steps were written for.

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Type

Stovetop pressure canner with dial gauge

Pressure canning

Yes

Water bath

Yes, quarts and smaller, per Presto

Liquid capacity

23 quarts

Jars per load

7 quarts, or 20 regular-mouth pints stacked

Altitude

You raise the pressure by altitude from the USDA tables. Water bath times also change with altitude.

Price class

Mid-range

Stated in: Presto Canner Comparison Guide (2025), read 2 November 2026

Why here: A stovetop pot with a dial gauge and a documented jar chart, in the type the National Center says its instructions were written for.

Best for: You want to pressure can low-acid foods (vegetables, meat, chicken, fish) and can stay near the stove.

• The National Center's advice was written for stovetop canners
• Seven quart jars, or up to 20 regular-mouth pints stacked, says Presto
• Also works as a water bath canner for quarts and smaller, says Presto
• Works on gas and on electric coil and smooth-top ranges, says Presto

• You watch the gauge and adjust the heat yourself
• The dial gauge needs an accuracy test every year, says Presto
• Presto does not list induction for this pot. The 01784 is its induction version

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If a word here was new to you, the glossary has short explanations. Learning what the pot does before you buy one is a very good place to begin.