This is a question we get asked often and I totally understand why; they essentially look the same and, even according to the National Center for Home Food Preservation, the difference can be as simple as their size.
The National Center recommends pressure canning in canners that fit a minimum of 4 quart (liter) jars. There are two significant reasons for this:
- The larger containers use more water, therefore take longer to heat (and extend total canning time)
- The metal in larger canners is generally thicker (this also extends canning times)
Most tested recipes (including all of them from the National Center for Home Food Preservation which we, and many others, believe to be the leading experts in safety) base their timing and tests on the longer heating and cooling periods of pressure canners.
As you’ll see in the link, they don’t recommend adapting the recipes for smaller cookers.
Thank you to Mary who asked this question most recently; it’s one we struggled with for a long time and I can’t believe I hadn’t written about sooner!