Adjusting pressure setting and processing time when modifying pressure canning recipe


When it comes to pressure canning, is there a "golden rule" or standard for modifying recipe pressure settings or processing times when you want to change the quantity of jars used?

For instance, I am interested in cooking and canning this Split Pea and Ham Soup recipe.

Unfortunately, the recipe only makes 2 quart jars. I have a Presto 23-quart canner that can fit more than 2, and so — if possible — I would like to scale the recipe up to cook enough soup for 4 or maybe 5 quart jars worth.

But if I stuff 4 or 5 quart jars into the canner, does the pressure setting for this recipe (10 PSI) or the cook time (90 minutes) change? If so, what's the general rule for figuring these types of modifications out?

Best Answer

No modifications are necessary.

The pressure of the canner entirely determines the temperature of the water around the jar, and you don’t start timing until the canner is at that temperature/pressure, so regardless of the scale you’re assured of processing for long enough. In a larger canner and/or a weaker stove the contents of the jars will end up being slightly more cooked because of the longer lag time before you start the timer, but there’s not much you can safely do about that, and for pea soup it will make literally zero difference.