The next morning, craving toast with jam, I opened a jar that hadn't sealed. It wasn't jam, it was syrup. Delicious syrup, but decidedly messy on a piece of toast. As were the rest of the jars. Back to the internet (where I had learned to make it in the first place) where most of the suggestions for this problem were.... use it for ice cream syrup.
I don't want ice cream syrup. This is my freezer.
Ice cream is not an option. Ice cubes aren't even an option.
So today I opened every jar, emptied them, rewashed, resterilized, and recooked the jam with a little additional pectin. This time it set. It might be golden, plum flavored cement by tomorrow....but by golly it won't be syrup.
Have a wonderful week!