hmmm it should not burn to coal ;-)
I burn in it a way that a spoon could still free it from the jar/pan/pot without too much hassle.
At least it is not "bitter" (while the orange jam I do is a bit bitter as I keep a bit of the white from the peel).
BTW I also prefer if the plums are still not too ripe (so they are kind of "stiff" instead of "soft"). So they keep a bit of soureness instead of being sweet all over the place.
PS: seems regardless of how we cook our jam we agree to one thing: it tastes ;-)
PPS: Do you now add a plum monster to your game?

bye
Ron