Updated May 2021. This post was originally written ten years ago, to warn people away from choosing a steam canner for their heat processing. However, new research shows that steam canners are safe and effective. Read for more!
What is a Steam Canner?
A steam canner is a piece of cookware that most often looks like an old fashioned cake carrier. It consists of a shallow pan, a fitted rack and a high domed cover and is designed to trap steam and release it in a very controlled fashion. You’ll sometimes see steam canners labeled as atmospheric steam canner, to differentiate them from pressure canners, which also use steam.
Occasionally, you also find boiling water bath canners that can also be used as steam canners. This only works with pots that have enough height to accommodate a high rack so that there’s enough water to create enough steam to keep the jars hot for the entire processing time.
Canning high acid foods is a process in which jars of food are exposed to heat for a prescribed amount of time. This does two things. It kills off any living microorganisms. And it forces the oxygen present in the jar to vent out, creating a situation in which a vacuum seal can form as the jars cool.
Traditionally, this heat processing is done in a boiling water bath canner, in which the jars are fully submerged in boiling water for 10 to 85 minutes (the processing time depends on the kind of food you are preserving). Boiling water is a highly effective method for transferring heat, and so this method of food preservation has long been considered the gold standard for home use.
How Does a Steam Canner Work?
Steam canners have long been a popular alternative to boiling water bath canners. Instead of requiring a full pot of boiling water, they use just a quart of two. That water is brought to a boil and the pot is allowed to fill with piping hot steam (a pure steam environment reaches the same temperature as boiling water, which is why it’s equally effective). The steam transmits the heat into the jars. This has the same effect as boiling water bath canning, as the heat from the steam also kills the microorganisms and forces the oxygen to vent.
However, until very recently, most canning safety experts advised home canners to skip steam canners. This is because there hadn’t been enough research done to prove its efficacy. However, in 2015, the University of Wisconsin released the results of a study, which found that steam canning can be used interchangeably with boiling water bath canning, provided the proper steps are taken.
How to Use a Steam Canner
Preparing jars for steam canning works just the same as boiling water bath canning (click here to read my instructions on how to process jars in a boiling water bath canner). You can even use your steam canner to heat the jars prior to filling.
- Fill the tray of the steam canner with the amount of water required by the manufacturer.
- Fit it with a rack and place your jars on top.
- Turn the burner on and start warming the jars.
- Remove one jar, fill it with your product, wipe the rim, fit it with a new lid and clean ring, and set it upright on the rack inside the canner.
- When all jars are filled, place the lid on the canner and bring it to a boil. Once the steam has reached the appropriate temperature (consult the manufacturer instructions to learn how to judge this for your particular pot).
- Once the pot is at temperature, set your timer for the amount of time required for your recipe (if you are above 1,000 feet in elevation, make the same processing adjustments that you would for boiling water bath canning).
- You may need to reduce the heat during the processing time. Too much steam can sometimes interfere with the jars’ ability to seal, so you want a controlled amount of steam, not wild bellows.
- When the time is up, turn off the heat and remove the lid. Let the jars cool in the pot for an additional five minutes to help prevent siphoning and to allow the seals additional time to set.
- Set the jars on a wooden board or folded kitchen towel to cool. When jars are fully cooled, remove the rings and test the seals. Wipe jars down if any sticky liquid leaked out during cooling. Sealed jars are shelf stable for the length of time recommended by the recipe. Any unsealed jars should be refrigerated and used promptly.
How to Choose a Steam Canner
If you’re shopping for a steam canner, I recommend getting one that can double as a boiling water bath canner. Steam canners are not recommended for products that need more than 45 minutes of processing, because they risk boiling dry at that point. If you plan on preserving tomato products (which have a longer processing period), getting a pot that can serve double duty will mean that your single pot can perform all tasks (and it will also triple as a stock pot).
I like the pots that have temperature gauges in the handle, so that you can easily monitor the temperature in the interior of the pot. This ensure that you will always have properly processed food.
Do you use a steam canner? Share your experience in the comments below!