Water Bath & Steam Canning
A boiling water canner or steam canner will safely can high-acid foods. Acidity may be natural, as in most fruits, or added, as in pickled food. High-acid foods contain enough acid to block the growth of botulinum bacteria, or destroy them more rapidly when heated. The term "pH" is a measure of acidity; the lower its value, the more acid the food. The acidity level in foods can be increased by adding lemon juice, citric acid, or vinegar. The temperature reached in a water bath canner or steam canner is effective for destroying yeast and mold organisms.
Recommended Canners for High-Acid Foods
Boiling Water Bath Canner
Most boiling water canners are made of aluminum or porcelain-covered steel; at least one stainless steel model is also available. Boiling water canners have fitted lids and removable perforated or shaped-wire racks. The canner must be deep enough that at least 1 to 2 inches of briskly boiling water covers the tops of jars during processing.
You may use a flat-bottomed stockpot with a bottom rack inserted for water bath canning. The pot used as a canner must be large enough to have lots of water boiling freely around the jars, and at least 1 to 2 inches over the tops of jars.
Steam Canner
The University of Wisconsin-Madison has published research indicating that an atmospheric steam canner may be used for canning naturally acid foods such as fruits, sweet spreads such as jam and jelly, some tomato products, or acidified foods such as salsa or pickles, as long as all the following criteria are met:
- Foods must be high in acid, with a pH of 4.6 or below.
- A research-based recipe developed for a boiling water canner must be used in conjunction with the atmospheric steam canner. The booklet accompanying an atmospheric steam canner can't be relied on to provide safe canning instructions.
- Jars must be heated before filling, and filled with hot liquid (raw or hot pack).
- Jars must be processed in pure steam at boiling water temperature. the canner must be vented before processing until a full column of steam appears.
- Processing time must be modified for elevation as required by a tested recipe.
- Processing time must be limited to 45 minutes or less, including any modification for elevation. The processing time is limited by the amount of water in the canner base. When processing food, do not open the canner to add water. Regulate heat so the canner maintains a temperature of boiling water.
