Martin wrote:
You could try tasting one? That's pretty much how we did it. They looked
kind of done a week or two back, but they were still very very sour. Left
them for the extra 10-12 days and they were lovely.
If we leave them too long the birds eat them.

Odd, I don't think we've had any bird damage on the grapes. The buggers
nicked nearly all the cherries, and the wasps got a lot of the grapes that
went over, but I haven't seen any birds near the grapes.