Many home preservers love steam canners (such as the Victorio), because they use less water and less energy and take less time to preheat than boiling-water canners. For at least two decades, however, the USDA and its Extension employees have warned that steam canners may be dangerous. This has kept a lot of people from buying steam canners and has made the people who swear by the devices at least a tad nervous.
A 2003 position paper published by Oregon State University detailed the concerns: Cold spots might occur between the jars or under the dome; steam might lift the lid of the canner, which would allow cold air to enter; jars might break or heat unevenly; the user might mistake cool vapor for steam and so might underprocess the jars; the user might be burned by steam.
The fears of breaking jars and uneven heating always seemed bogus to me. The supposed problem was that the jars weren’t separated by a rack. Racks that come in boiling-water canners are usually divided into sections, one per jar, but many people do their boiling-water processing with unsectioned cake racks or pressure-canner racks or even with towels instead of racks. Most home preservers know better than to jam their jars tightly together in a canner.
I’ve never used a steam canner myself, but I’m pretty sure that the vent holes in the side must keep the lid from lifting off like an umbrella in the wind.
Steam burns seem like a true risk with steam canners, but you get a faceful of steam if you’re careless in opening a boiling-water canner, too.
Now Dr. Barbara Ingham, of the University Wisconsin-Madison, has actually done some research on steam canners, and she has found they work pretty well. She has convinced the National Center for Home Food Preservation, the USDA division that oversees home canning, to approve the use of steam canners.
Dr. Ingham, however, identified one important limitation of steam canners: They hold too little water to allow for processing times of more than 45 minutes. This presents no problem for pickles and jams, but the USDA recommends processing tomatoes for long periods, from 35 to 85 minutes (or even longer at high altitudes), depending on how the tomatoes are prepared. You could use a steam canner for tomato sauce or juice, but a boiling-water canner or even a pressure canner is probably a better choice. If the boiling is too vigorous in a steam canner, Dr. Ingham found, the pan can boil dry in twenty minutes.
Dr. Ingham suggests some guidelines to follow with steam canners:
- Use USDA recipes; don’t rely on the instructions that come with the canner.
- Fill the jars with hot liquid, and put them into the canner while they are still hot.
- Make sure that a 6- to 8-inch jet of steam streams from the vent holes throughout the processing period.
- If possible, check the temperature of the steam—it should measure 212 degrees F—by inserting a thermometer through a vent hole. (Actually, if you live above sea level the temperature will be somewhat lower.)
- If you’re canning at an altitude of 1,000 feet or higher, you should process your jars longer, just as you would in a boiling-water bath.
- Let the jars cool at room temperature, as usual.
According to Jeanne Brandt, Family and Community Health director for Oregon State University Extension, OSU still doesn’t like steam canners. But I think I might give one a try.