Yes, you can double or triple a Pomona’s cooked recipe. Be sure to double or triple all of the ingredients in the recipe.
Potential Limits and Pitfalls when doubling or tripling a recipe:
You must have a water-bath canner that is large enough to hold ALL of the jars you are filling. It is not safe canning practice to let some of the filled jars sit on the counter while you water bath others. As soon as all the jars are filled and have their lids on, they should ALL go into the boiling water in the canner.
You must have a pot that is large enough to hold all of the fruit in the recipe plus the added ingredients, with enough extra room to stir vigorously while the mixture is boiling and not have the contents spill over.
You must have a stove that is powerful enough to bring the fruit mixture to a full boil and to bring it back to a full boil in a few minutes after you stir in the pectin-sweetener mix. If the fruit mixture with the pectin in it takes too long to return to a full boil, the pectin can be de-activated and you will get runny jam.
You must have a stove that is powerful enough to bring a large water bath canner with all of the filled jars in it back to a rolling boil in a few minutes so as not to de-activate the pectin by extended exposure to heat while waiting for the boil to come back.
We do not recommend quadrupling a recipe unless you are specifically set up for it.