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Equipment · Atmospheric steam canners
steam canner
A shallow rack base and tall vented cover process jars in atmospheric steam. NCHFP limits the method to tested high-acid or acidified recipes requiring no more than 45 minutes, including altitude adjustment; this is not pressure canning.
An atmospheric steam canner is a separate cooking vessel for heat-processing jars. In the documented dome-style form, a shallow base holds a rack above a small amount of water; a tall cover encloses the jars, and vent holes let air and then steam leave the canner. Some models have a temperature gauge in the lid. Penn State Extension describes this base–rack–cover construction, while the University of Minnesota Extension describes lightweight aluminum as a typical material. Those are common features, not a specification for every model.
The heat medium matters. Water boils in the base and produces steam that surrounds the jars. NCHFP distinguishes this atmospheric device from pressure canners: it is not a pressurized vessel and must not be substituted for pressure canning low-acid foods. An ordinary lidded pot is not equivalent to the vented equipment described in the research.
NCHFP says atmospheric steam canners may be used for naturally acidic or properly acidified foods with an equilibrium pH of 4.6 or below, provided that users follow research-tested recipes and the required controls. This includes appropriate tested processes for foods such as fruit, jams, jellies, pickles and salsa. The device does not make an untested recipe safe, and its convenience does not broaden the foods that may be processed in it.
Processing time is capped at 45 minutes after any altitude adjustment. The limit comes from the finite water held in the base. If a tested recipe requires a longer total process, the steam canner does not meet that condition. The recipe, jar size, preparation and processing time belong together; a seal on a cooled jar does not replace the required tested process.
Before timing begins, air must be driven out so the jars are exposed to pure steam. NCHFP's current statement adds a direct temperature check at the side vent: wait for a steady column of steam and confirm that it is 210–212°F, with the exact reading dependent on elevation. Maintain the proper steam conditions throughout the timed process and follow the instructions supplied for the exact model.
The canner stays closed during processing. The water reservoir cannot be topped up by opening the cover mid-process; the limited reservoir is part of the method's time constraint. After the processing interval, NCHFP's updated guidance says to turn off the heat and leave the lid in place for five minutes. Remove the jars carefully and let them cool in still room air; forcing faster cooling changes the validated procedure.
The National Center for Home Food Preservation reports that the University of Wisconsin, working with NCHFP, studied steam temperature distribution, jar-heating patterns and standardized cooling. The results were published in a peer-reviewed paper in 2015. This is a date for the modern evidence base, not an origin date for steam canners. The sources reviewed here do not identify one inventor, a single manufacturing origin or a universal design.
The linked Penn State Extension photograph, credited to Martha Zepp, shows one real example with a shallow rack base and a tall cover. It is a reference for visible equipment form, not a claim that every photographed jar or model is suitable for every recipe. The generated illustration separates the parts for clarity and leaves out food; it is editorial art, not a product specification or a safety test.
National Center for Home Food Preservation summary of Wisconsin/NCHFP research and 2015 peer-reviewed publication.
Use only an up-to-date research-tested recipe for naturally acid or properly acidified foods at pH 4.6 or below; low-acid foods require a pressure canner.
Source →Total processing time, including altitude adjustment, must be 45 minutes or less; follow the tested recipe and the specific canner manufacturer's instructions.
Source →The canner must be vented and maintain pure steam at the temperature of boiling water; do not open it during processing. Cool jars in still ambient air.
Source →NCHFP's updated guidance calls for checking vent steam at 210–212°F, depending on elevation, before timing, and leaving the closed canner undisturbed for five minutes after processing.
Source →The location records documented research and home-preservation guidance in the United States; it does not claim an exclusive place of invention or use.
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National Center for Home Food Preservation, University of GeorgiaEquipment · History · Safety
National Center Burning Issue: Using Atmospheric Steam CannersThe atmospheric steam canner is used for naturally acid or properly acidified foods with pH 4.6 or below, not for low-acid foods.
NCHFP describes a dome-style steam environment and key controls: vent air, maintain pure steam at boiling temperature, use preheated jars, adjust for altitude and limit total processing to 45 minutes.
The canner's limited base-water volume means it must not be opened during processing to add water; jars cool in still ambient air.
NCHFP says the University of Wisconsin/NCHFP research was published in 2015.
Cited in: A canner that uses steam without pressure; What the research supports; Venting, temperature and cooling; A research-tested modern tool
National Center for Home Food Preservation, University of GeorgiaSafety · Current guidance
Atmospheric Steam Canning StatementNCHFP identifies atmospheric steam canning as a method for high-acid foods when tested recipes and current guidelines are followed.
NCHFP's updated statement asks users to confirm vent-steam temperature at 210–212°F (depending on elevation) before timing and leave the lid in place for five minutes after processing.
Cited in: Venting, temperature and cooling
Penn State ExtensionEquipment · Image reference
How to Use an Atmospheric Steam CannerPenn State describes the apparatus as a base, rack and cover; the shallow base holds the rack above water and the tall domed cover has one or two vent holes; some models have a temperature gauge.
The source page's photograph is credited to Martha Zepp, Penn State University, and shows a dome-style canner, shallow rack base and jars.
Cited in: A canner that uses steam without pressure; A research-tested modern tool
University of Minnesota ExtensionEquipment · Safety
Preserving food at home: CanningUMN describes a typical canner as lightweight aluminum with a shallow base and rack, a tall dome cover with side vent ports and a lid temperature sensor or gauge.
Atmospheric steam canning is for naturally acidic and acidified foods; low-acid foods require pressure canning.
The canner's steam vents and adequate pure-steam heating distinguish it from an ordinary pot.
Cited in: A canner that uses steam without pressure