Oops, I forgot to post a picture of the grapes and the discoloration!

What does the foliage look like? Grapes are prone to a good number of fungal issues, most of which will affect the leaves as well as the fruit and often the stems too. If you see signs of discoloration (whitish/gray spotting) on the leaves as well, you could be experiencing powdery mildew. Too late to do anything about it now although you may want to consider a dormant spray this winter to take care of any overwintering spores.

The fruit formation doesn't look very good either but that may well be due to youth (Did they not tell you NOT to let your vine fruit this first season?).