Plum juice

I have a plum tree in my backyard. I think it needs to be trimmed down a bit, it has a lot of plums, and they are real small and very tart. They really aren't edible unless you leave them on the tree to ripen and they're still very small and if they get ripe the birds get them.

I don't really know how much sugar they have in them. So, I've started picking them way before they ripe, just as they turn color, and throw a handful in a pot of water to boil for while, then drain off the water, mixing it with some lemon juice/artificial sweetener mix I drink a lot.

It actually comes out pretty good. The plums are tart but they still soften the lemon.

I just wonder about the sugar levels.