[rowlandwells]

we usually put some of our plumbs in the freezer for winter use but we  found them to be very sour to eat after they came out the freezer although we did put sugar with the plumbs prior freezing but we found the plumbs sour after cooking

the same has happened when  freezing strawberries they where sweet tasting before we put them in the freezer but yet again needed sugar because they where sour after they came out the freezer

any advise on this topic would be most helpful

[New shoot]

Is the fruit leaking a lot of juice when you defrost it?  That could be taking the sweetness out and putting sugar in with the fruit would encourage even more juice to leak.

I always freeze fruit in a single layer, then bag it up and I don't put sugar in.  It prevents damage to the fruit and makes sure you can spread it out to defrost quickly.  I sweeten it when it has defrosted and I am ready to use it 

[MrsPea]

Have you tried stewing your plumbs first then freezing them, that's how i do mine, it might depend on which plumbs they are mine are Victoria.

[TonyB.]

Old fashioned I know but I remember my mom (our fridge was a marble slab in the pantry and did not have a freezer - it was a long time ago). She used to do pears and plums in kilner? jars for winter use.