I've made blueberry jam many times with great success. This year I decided to try a new recipe (Alton Brown's) that called for using vinegar. Because I had purchased some low sugar pectin, I used less sugar than in the recipe. Not surprising in retrospect, the jam turned out too tart.
Question: Although it has been several weeks since I processed the jam, can I empty the jars in a pot, add more sugar to reduce the tartness and then reprocess in a hot water bath?
I really hate to throw out the jam, but it is just too tart to gift and the quantity is too great for me to keep.