A Guide to Using Steam Canners

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Steam canners have been around since at least the early 1900s, but for many years the United States Department of Agriculture maintained that steam canning is unsafe. Last year, the USDA finally published guidelines for safely processing high-acid foods in a steam canner. Here’s the latest scoop on steam canners and how to use one.

Atmospheric Steam

A steam canner, also called a steamer, is a vessel that processes food in jars by surrounding them with steam, which has the same temperature (212ºF) as boiling water. Steam canning differs from pressure canning in occurring at ambient atmospheric pressure, rather than under increased pressure. To differentiate steam canning from pressure canning (which will be discussed in the May/June 2017 issue), the former is sometimes called atmospheric steam canning.

In a steam canner, the bottom is filled with a few inches of water, the jars are placed on a rack or a platform that elevates the jars to the water line, and a cover with one or more vent holes is placed on top of the canner. When the water in the canner comes to a boil, it evaporates as steam that surrounds and thoroughly heats the jars at a safe temperature for processing home canned foods.

Compared to water bath canning (described in the January/February 2017 issue), steam canning uses considerably less water — only 2 to 3 quarts versus up to 4 gallons in a water bath canner. The water, therefore, heats up faster than in a water bath canner, requiring less energy, as well as less of your time waiting for water to boil.

Because it uses less water and energy, a steam canner reduces expenses for water and fuel, and won’t heat up your kitchen as much, which can be a big plus on a hot summer day. Proponents of steam canning like to point out as another advantage that the water won’t boil over onto your stovetop. On the other hand, a steam canner may run dry if you fail to precisely follow prescribed procedures.

Any foods that may be safely processed in a water bath canner may be safely processed in a steam canner. These are high-acid foods — having a pH of less than 4.6, such as most fruits, jams, and pie fillings — for which tested recipes have been approved by such reliable sources as The National Center for Home Food Preservation (nchfp.uga.edu) and Ball (freshpreservingstore.com). Processing times are the same for steam canning as for water bath canning.

The one restriction for the type of high-acid foods that may be steam canned is that the required processing time cannot be greater than 45 minutes, including any necessary adjustment for elevation. Otherwise, the steam canner may run dry, in which case the food will not be properly processed, the canner could be ruined, and even your cooktop may be damaged.

Most high-acid products that require more than 45 minutes for processing involve tomatoes, and for those you would need to use a water bath canner. One steamer, the Victorio multi-purpose canner, doubles as a water bath canner. It comes with a reversible rack that looks like a regular water bath jar rack, but when flipped upside down becomes a steamer rack. The boiling water feature lets you process recipes requiring more than 45 minutes, while the steam feature is suitable for all others.

Steamer Construction

Steam canners come in two basic styles, both of which will process seven one-quart jars at a time. One style is offered by both Victorio (victorio.info) and Back to Basics (westbend.com/steam-canner.html). It is an aluminum unit consisting of a shallow base, or water pan, coupled with a tall cover, or steam dome. In the side of the dome, one small hole (Victorio) or two (Back to Basics) serve as vents to release steam. A rack in the water pan elevates the jars above a few inches of water.

The second style is Victorio’s multi-use canner, which comes in either aluminum or stainless steel. It looks much like a stock pot, except it has steam vents in a glass lid, and comes with a reversible jar rack that may be used for both steam canning and water bath canning.

With their flat bottoms, multi-use canners may be used on a smooth radiant heat cooktop, but only the stainless steel version is suitable for use on an induction cooktop. Dome-top steamers, being aluminum, are not suitable for induction cooktops. And, since they have ridged bottoms, they won’t work efficiently on a radiant heat cooktop but may be used with any standard electric coil or gas range.

To monitor temperature during processing, all Victorio models have a built-in thermal sensor in the cover, which provides assurance that steam is maintaining the correct processing temperature. With the Back to Basics canner you must either rely on seeing steam coming from the vents or purchase a thermometer to periodically insert into a vent hole. For this purpose, Professor of Food Science Barbara Ingham, of the University of Wisconsin, recommends using a tip-sensitive digital thermometer, not a dial stem thermometer, because the latter must be inserted farther into the canner and the jars inside would interfere.

Among tip-sensitive digital thermometers, a thermocouple thermometer will give you the fastest reading and may be calibrated for accuracy. A thermistor-style thermometer is slightly slower and some brands cannot be calibrated. Unless you have other uses for one, a quality thermometer of either style will run you more than a canner with a built-in thermal sensor. An alternative to using a thermometer is to put a nickel in the water pan.

Boiling water will cause the nickel to bounce. As long as you hear the coin rattle steadily, the water is boiling.

Steamer Procedure

Using a steam canner involves these basic steps:

1. Keep your washed canning jars warm until they are filled for processing.

2. Put the rack in the canner and add the amount of water recommended for your model, typically 2 to 3 quarts.

3. Heat the water in the canner, but don’t bring it to a boil yet.

4. Fill the hot, clean jars according to the recipe you are following for the specific type of food you are canning. You may use any reliable recipe intended for water bath canning, provided the processing time is not greater than 45 minutes. Reliable recipes may be found online at official sites such as nchfp.uga.edu and freshpreservingstore.com.

5. Regardless of whether the recipe you are following calls for hot pack (in which the food is preheated) or raw pack, cover the food in the jars with hot liquid.

6. To keep jars from cooling until processing starts, place the jars on the rack in the warming water pan as they are filled and fitted with lids and bands.

7. Put the cover on the canner, turn the heat to the highest setting, bring the water to a vigorous boil, and watch for steam to stream through the canner’s vent(s). Use either the canner’s built-in thermal sensor or a tip-sensitive digital thermometer to monitor temperature.

8. Start your timer when the temperature reaches 212°F and a steady column of steam flows freely from the canner vent(s). Processing times for steam canning are the same as those published for water bath canning. If your elevation is above 1,000 feet, adjust the processing time according to the Elevation Table on this page.

9. Gradually reduce the heat to maintain a steady 6- to 8-inch column of steam without letting the water boil vigorously, which may cause your jars to leak liquid (called siphoning) or break, and may also cause the canner to run dry. Do not open the canner at any time during processing.

10. When the time is up, turn off the heat, remove the lid from the canner (open the lid away from you to avoid being burned by steam), and leave the jars in the canner for 5 minutes more.

11. Using your jar lifter, remove the jars, one by one and place them, one inch apart, on a rack or thick towel away from drafts.

12. Let the jars cool for at least 12 hours before removing the bands and testing the seals.

Dr. Barbara Ingham and her team at the University of Wisconsin developed guidelines for safe steam canning. Dr. Ingham invites anyone with questions about steam canning to contact her at bhingham@wisc.edu.

Canning Code

HOT PACK. Cooked or preheated food used to fill canning jars for processing.

HIGH-ACID FOODS. Pickles, fruits, jams, jellies, juices, and other foods with a pH less than 4.6.

JAR LIFTER. A device for safely putting jars into or removing them from a hot canner.

MULTI-USE CANNER. A vessel that may be used for both steam and water bath canning.

RAW PACK. Fresh produce that has not been cooked or preheated before being placed in jars for processing; also called cold pack.

SIPHONING. The leaking of liquid from jars during processing, usually resulting from a too-rapid change in temperature.

STEAM CANNER. A large vessel in which jars of food are processed surrounded by atmospheric steam.

STEAM CANNER RACK. A platform that holds jars above boiling water so steam can circulate around them during processing.

VENT. A hole in the side or top of a steam canner through which excess steam is released.

Keep It Steaming

During steam processing, the jars in the canner must be continuously surrounded by steam throughout the entire time in order to maintain an adequate temperature for safe food storage. Three things can reduce the flow of steam: turning the heat too low, lifting the canner’s cover while jars are being processed, or boiling the canner dry.

Water that boils too hard during processing may evaporate before the processing time is up. Total evaporation can occur in as little as 20 minutes. Once a vigorous boil has been reached, indicating that the steamer has reached the proper temperature, gradually turn the heat down until the water reaches a slow rolling boil — enough to maintain a steady, unbroken column of steam emitted through the vent hole(s). Use either your canner’s thermal sensor or a tip-sensitive digital thermometer periodically inserted into a vent hole to verify that the temperature is correct.

As long as you see steam steadily coming through the vent(s), you should have no reason to open the canner until the processing time is over. If you are the sort who can’t resisting looking to see what’s going on inside, consider using a steamer with a glass lid. For an audible clue, put a nickel in the bottom of the canner; it will bounce and rattle as long as the canner contains water and the water is boiling.

If the water stops boiling at any time during processing, the correct temperature will not be maintained and the jars will not process properly. Increase the heat until venting resumes, then reset your timer to the full processing time. If the canner runs dry before the time is up, stop, replenish the water, and start over again. When using a steam canner to process one batch after another, always check the water level and replenish it as needed between batches.