I noticed plenty of old black grapes hanging from this vineyard as I walked along the perimeter. Many were shriveled as if the moisture had been sucked out of them, but this little bunch was still fairly red, and young-looking.
I decided to try one of the black and one of the red ones - just to compare. The black, slightly deflated, grapes were fairly sweet while these red ones were pretty much the opposite - a little tart. So, i had another slightly deflated black grape. :)
I'd never actually walked along a vineyard, eating grapes, and while I only had about 5 in total, I have to say that it was a somewhat pleasant experience. You should try it some day.