How does Ball mason jar size affect canning processing time?

Question

I'm new to canning and food preserving and bought a basic starter kit including a water bath canner (I'll get into pressure canners later if I have success with this method).
One thing that is often cautioned is that the size of the container (pint or quart Ball mason jar) affects the cooking/processing (boiling) time, as well as the altitude!
Interestingly enough, in most recipes I see specific values given to adjust the processing time based on altitude (for example: if between 3000 and 6000 ft above sea level, add 5 mins to the processing time, etc.).
However, I have never seen anything that tells me how the jar size affects the processing time! Does anybody know if there is a rule of thumb here?

rumtscho · Accepted Answer

As pretty much always in canning, there are no rules of thumb for calculations/changes (the altitude thing is an exception, admittedly).
Each recipe has been developed and tested for a given jar size, and the institution which developed it should give you the size of jar you have to use. You cannot change the size to a larger one and add some number of minutes.
In general, you can change the recipe to a smaller jar size, but without reducing the time. This ensures that you don't run into problems with food safety, but you will likely end up with an overcooked product.
Bottom line, don't change jar sizes on your own, use the ones in the recipe.

How does Ball mason jar size affect canning processing time?

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