How do you determine if canning is safe?

Canning is safe when the method matches the acidity of the food: a boiling water bath for high-acid foods such as fruits, jams, jellies, pickles and salsa, and a pressure canner for low-acid foods such as vegetables, meats, poultry and seafood. The pressure canner is the only method the USDA recommends for those low-acid foods, because only pressure reaches the temperature that destroys the spores behind botulism in a low-acid jar.

Everything else on this page follows from that split and from what the makers of the canners in our two guides publish about their machines. Nobody at Lush has used these products. The figures below are the makers’ own published specifications, and where a maker publishes nothing, we say so.

Start with the acidity of the food

The single decision that makes a batch safe or unsafe is whether the food is high-acid or low-acid. Fruits, jams, jellies, pickles and most salsas carry enough acid that a boiling water bath at around the boil is sufficient. Vegetables, meats, poultry, fish, broths and sauces do not, and they need the higher temperature that pressure delivers. A recipe that puts a low-acid food through a water bath is the classic unsafe jar, no matter how long it boils.

Our guide to Best Electric Canners for Pressure and Water Bath Preserving compares machines that handle both sides of that line. The Presto 02144 12-Quart Digital Pressure Canner is described by its maker as the first digital canner that automates both pressure canning and water bath canning, and Presto states that it meets USDA guidelines for low-acid foods such as meat, poultry, fish and vegetables, with no adjustments needed for high altitudes. That last point matters: altitude changes the pressure needed, and a canner that states it handles the adjustment removes a step where home canners commonly go wrong.

NESCO describes its NPC-9 as a dedicated electric pressure canner with built-in safety controls that automatically regulate pressure and temperature, and lists pressure cook, slow cook, steam and water bath among its modes. The maker’s published capacity for that model is 9.5 quarts in the product title and 9 quarts in the size field, so the two figures do not agree; we report both rather than pick one.

Match the canner to the method

A water bath canner is a large pot of boiling water with a rack that keeps jars off the bottom. It cannot exceed the temperature of boiling water, which is why it is limited to high-acid foods. Our electric canner guide includes several machines built for that job. The WantJoin water bath canner is listed at 33 quarts in its title and 30 quarts in its feature text, holds up to 11 one-quart jars according to the maker, and offers adjustable temperature from 86 to 212 degrees Fahrenheit with a timer from 30 to 180 minutes. The McSunley Prep-N-Cook is a 21.5 quart stainless steel pot whose rack, per the maker, holds 7 one-quart, 9 one-pint or 12 half-pint jars.

A pressure canner is a different instrument. It seals, builds pressure and reaches temperatures above boiling, and it carries safety hardware for that reason. Our guide to Best Pressure Canners for Large-Batch Home Canning compares five of them. The Presto 01784 23-Quart Induction Compatible Pressure Canner is described by Presto as the only method recommended by the USDA for preserving vegetables, meats, poultry and seafood, and the maker lists space for 7 quarts, 20 pints or 26 half-pints of regular Mason jars. It also states an air vent and cover lock that lets pressure build only when the cover is properly closed and prevents opening until pressure is safely reduced.

The All American 921 is a 21.5 quart pressure cooker and canner that the maker says holds approximately 19 pint jars or 7 quart jars, and it uses a machined metal-to-metal seal with no gasket, plus a steam gauge and a regulator weight. The Siftary 24 QT canner is listed with a gauge calibrated to 14.5 PSI and dual over-pressure relief valves. The RVGMBO 12 quart cooker lists adjustable settings from 15 PSI at high to 10 PSI at low.

Read the safety features the maker lists

Safe canning depends on the vessel holding pressure and refusing to open while it does. Every maker in our pressure canner guide publishes something on this. Presto lists the air vent and cover lock described above. All American lists its clamping locks and metal-to-metal seal. RVGMBO lists a secure-lock lid, safety valve, lid window and pressure release valve, and states that the lid stays locked if internal pressure increases. Siftary lists a secure locking lid and dual over-pressure relief valves. Hestroney describes a six-part protection system with pressure release valves, safety valves and self-locking valves.

On the electric side, Presto states that its digital canner has ten built-in safety features, including a cover-locking system and a sensor that automatically holds the correct temperature. NESCO lists a safety lock lid, an automatic float valve and a pressure regulation system that prevent opening under pressure. Those are the maker’s claims, not our observations. What follows from them is simple: a canner with a lock that is tied to internal pressure is doing part of the safety work for you, and a pot with no such mechanism, such as a plain water bath pot, is not under pressure in the first place and does not need it.

Check capacity against your batch

Capacity does not make a batch safe or unsafe, but it changes how you load and process. The makers publish jar counts for most of these models. Presto’s 01784 takes 7 quarts, 20 pints or 26 half-pints. All American’s 921 takes about 19 pints or 7 quarts. McSunley’s rack holds 7 quarts, 9 pints or 12 half-pints. WantJoin states 11 one-quart jars. The NESCO NPC-9 is listed at 9.5 quarts with canning and steam racks included, and Presto’s 02144 is a 12 quart model. The Siftary is 24 quarts and the RVGMBO is 12 quarts; the Hestroney is listed at 10.6 quarts.

Two of the pressure canner picks publish no dimensions at all: Siftary and Hestroney give no width, depth, height or weight. The makers do not publish those figures, and this site has not compared them. Where a maker publishes a jar count, use it to plan a single even layer or a stack, and keep the load within what the maker states rather than packing to the rim.

What the published figures cannot tell you

No specification sheet can certify that a particular jar of food is safe. The maker’s pressure rating, lock design and stated USDA compliance describe the machine, not your process. The parts that decide safety are the acidity of the recipe, the processing time and pressure for your altitude, and a clean seal on the jar. Presto states that its 02144 needs no adjustment for high altitudes, which is unusual and worth noting; for other models, follow the maker’s instructions on altitude rather than assuming.

This site has not tested any of these canners, has not timed a batch, and has not measured pressure. We report what the makers publish. Where a figure is missing, such as the dimensions of the Siftary and Hestroney models, we say the maker does not publish it. A canner that lists its safety hardware and its USDA position gives you more to check against your recipe than one that lists neither, and that is the most a published specification can do.