hazard a guess?
On August 12th I looked at my grape arbor and noted that my grapes were ripening and would be ready to pick in 4 or 5 days. On August 15th I was dismayed to discover that the entire crop was gone! Since you are too far away to offer a tissue to dab my eyes, can you hazard a guess as to what might have happened? We have deer, squirrels, raccoons, fox. Might they have eaten them? The clusters were stripped with the central stem still hanging on the vines. Some grapes, but not many, were on the ground, some of which were punctured. Might our heat wave ripened them so fast that they fell off the vines in a thunderstorm? Or might the culprit have been black rot which I have been fighting in the vineyard? This year for the first time I have followed completely the recommendation for spraying with captan, having done spraying sporadically the last few years. The black rot was still in about 20% of the vines. All this verbiage is to ask for your guess as to what I could/should do to have grapes to enjoy next year. The vines (mostly Concord and Fredonia) are 50 years old and very vigorous.
Sounds like the damage was a type of wildlife. We cannot say for sure but you may be dealing with deer and/or birds. Next season you will have to consider fencing and/or netting. Netting should be in August and September.
Here is a FAQ page on wildlife and grapes