How to Use an Atmospheric Steam Canner

Research by the University of Wisconsin-Madison indicates that an Atmospheric Steam canner may be safely used for home canning of high-acid foods.

What Is an Atmospheric Steam Canner?

• The atmospheric steam canner consists of three major pieces—a base, a rack, and a cover. The traditional steam canner base is only three inches high. Inserted in the base is a rack to keep the jars above the water. The cover is a high dome and includes one or two holes through which steam vents. Some models include a temperature gauge.

Differences between a Steam Canner and a Pressure Canner

• Are you confused as to how an atmospheric steam canner differs from a steam pressure canner? Seems as if a lot of people are.
• Generally, these canners are simply referred to as a steam canner or a pressure canner. However, a pressure canner is a sealed unit that produces temperatures higher than the boiling point of water.  When the pressure canner is vented for ten minutes, air is driven from the canner and the jars are surrounded by steam. Applying a weight or pressure regulator builds up pressure, and the temperature inside the canner reaches 240°F at 10 pounds pressure in a weighted gauge canner or 11 pounds pressure in a dial gauge canner. This is adequate to inactivate C. botulinum spores that can cause the serious illness, botulism. A pressure canner is absolutely essential to process low-acid foods, including all meats and vegetables (except acidified tomatoes or pickled products).
• A steam canner operates in the surrounding atmosphere. When the canner has been vented as described below, the remaining steam inside the canner will be 212°F, which is the same temperature as boiling water.

Safety Criteria

To safely use an atmospheric steam canner, certain criteria must be met.

Select High Acid Foods.

• Foods must be high in acid with a pH of 4.6 or below.  These include fruits such as peaches, pears, and apples, as well as acidified foods such as salsa or pickles. Fruit-based jams and jellies can also be processed in an atmospheric steam canner.
• Acidified tomato products with a process time under 45 minutes may be canned in an atmospheric steam canner.
• All the above foods can also be safely processed in a boiling water canner.

Use only research-tested recipes developed for a boiling water canner.

• Approved recipes are available from sources such as the National Center for Home Food Preservation or from Penn State Extension. Sources of hard copy recipes include the books So Easy to Preserve, (Andress, E. and Harrison, A.; University of Georgia, Bulletin 989, 2014) and Preserving Food at Home Resource Guide (Penn State Extension, 2022).
• Follow a research-tested recipe using the steam canner instead of a boiling water canner at the processing step.
• Avoid using recipes in the instruction guide that comes with the atmospheric steam canner because some guides include untested recipes.

Process in pure steam at 212°F.

• Option 1: Check the temperature inside the canner with a thermometer placed in the vent hole. The placement of jars in the canner may make this difficult.
• Option 2: Watch for venting prior to starting the processing time. Turn the heat to medium high under the canner, and watch for a full column of steam at least 8 inches long to flow from the vent hole(s).
• Begin timing the process after a full column of steam forms.
• Steam has to flow freely from the canner vent(s) during the entire processing time, or the food is considered underprocessed (and possibly unsafe).
• Some atmospheric steam canners come with a built-in temperature sensor in the lid that indicates when the internal temperature is safe for processing at a given altitude. See instructions for testing these sensors at the end of the article.

Adjust processing time for altitude. 

• Elevations above 1,000 feet require longer processing times because water boils at a lower temperature as elevation increases. 
• An easy method of finding the elevation where you live is to search "elevation" and your address on your computer or cell phone.

Use standard canning procedures, jars, and lids.

• Fill the base with about two quarts of water—just below the level of the rack. One manufacturer recommends starting with cold water to avoid softened water that may contain salts, which may eventually cause corrosion of the metal. You can add a tablespoon of white vinegar to the water.
• Use standard canning jars and two-piece lids.
• Half-pint, pint, or quart jars may be used as specified in tested recipes. Half-gallon jars cannot be used.
• Heat jars prior to filling. Either heat jars in another pot of hot water or partially fill jars with hot water and place in the steam canner until ready to use. Drain and fill.
• Pre-heating the canner helps to keep the jars hot after filling.  Pre-heat the water to 140°F for raw-packed foods and to 180°F for hot-packed jars.
• Use either a raw or hot pack as appropriate and fill jars with hot liquid, allowing correct headspace.

Time Limit is 45 minutes

• Processing time is limited to 45 minutes or less, including any adjustments for elevation.
• Because water evaporates when boiling, the processing time is limited by the amount of water in the canner base.
• A canner that boils too vigorously can boil dry within 20 minutes. Food in a canner that boils dry is considered under-processed and potentially unsafe.
• Do not open the canner to add water during processing because steam will escape and the temperature will drop.
• Regulate heat so that the canner maintains a temperature of 212°F. Bring the canner to that temperature at medium-high, then adjust the temperature to maintain that temperature. The lid should not jiggle, and the vents should not whistle.

After Processing

• When processing is complete, turn the heat off the burner and allow the jars to sit in the covered canner 5 minutes. (This 5-minute wait time reduces siphoning.)
• Remove the cover and place jars on a cloth-covered counter or wooden board or rack away from drafts.
• Caution:  the steam and water will be hot!

Temperature Sensor Test

• If your canner has a temperature sensor, you should test it yearly and when you change the elevation of its use according to VKP Brands.
• Place 4 quart jars filled with water in prepared canner—no need to place lids on jars.
• Bring to canning temperature.
• When the lid starts lifting, rattling, or spitting water from around the edges, the temperature is almost up to the desired level.  Slowly turn the heat down until these actions stop.
• Continue watching the sensor until the needle stops rising.  The needle should reach the green area for your zone, but it can vary from just reaching the green area to going far inside it.
• Mark this maximum point on the sensor or make a note of its position. This is the boiling point at which it is safe to start the processing time.

References

1. Fruitsaver Steam Canner Instruction Manual, VKP Brands, Kitchen Crop, c. 2021.

2. Hirneisen, A., LaBorde, L., McDonald, S., McGeehan, N., & Reed, S. (2022). Preserving Food at Home. Penn State Extension.

3. Williams, K., (Consumer Consultant, VKP Brands,) phone interview September 13, 2021.

4. Willmore, P., Etzel, M.,  Andress, E., & Ingham, B. 2015.  Home Process of Acid Foods in Atmospheric Steam and Boiling Water Canners.  Food Protection Trends. 35:150-160.