A pressure canner is the essential piece of equipment for safely canning low acid foods such as soup stocks and un-pickled vegetables. But did you know that it can double as a boiling water batch for fruits, pickles, jams and jellies? The instructions are different than those for pressure canning or standard boiling water bath processing. Here's how to do it.
Place the pressure canner on the stove. Put a rack in the bottom of the pressure canner (most pressure canners come with one). Place your jars of food on the rack, leaving space between the jars. Pour in hot water just until it comes up to the shoulders of the jars (about 1 1/2 inches below the lids of the jars)
Notice that the last instruction above is different from the usual boiling water bath instructions. For regular boiling water bath canning in an open pot you must cover the jars completely with 1 - 2 inches of water above the lids. When you use a pressure canner as a boiling water bath, the water only comes up to the shoulders of the jars.
Screw or clamp on the lid of the pressure canner and leave the vent, or petcock, open. Turn on the stove to high heat. When steam starts coming out of the vent vigorously, start timing your boiling water bath processing time according to the instructions in the recipe for whatever you are canning.
This is the other instruction that varies from business-as-usual canning. If you were pressure canning, you would leave the vent open for 10 minutes, then close it to start building up pressure in the canner. When you use a pressure canner as a boiling water bath, leave the vent open for the entire processing time.
Remember that the processing time doesn't start when you turn on the heat, but rather when steam starts blasting through the vent. So for example, if a canning recipe ends with the instruction to "process in a boiling water bath for 20 minutes," you don't start timing that 20 minutes until you see and hear steam escaping.
Wait until the hissing sound of escaping steam ceases before taking off the pressure canner lid and removing the jars.
Important: remember that even though you are using a pressure canner, with this method you are processing the food in a boiling water bath. This cannot be used in lieu of pressure canning. The same safety rules apply as with regular boiling water bath canning, i.e. you can only use this method for fruits, sweet preserves, tomatoes with added acid and pickles (including vinegar-containing chutneys). All un-pickled vegetables and animal products must be processed using your pressure canner as, well, a pressure canner.
I find it most useful to use my pressure canner as a boiling water bath when I've got more jars to process than will fit in the pot I normally use for boiling water bath canning. It's also convenient if I'm going from a boiling water bath project to a pressure canning project. I just leave the canner on the stove, ready to go from one method to the next.