Answer: Unfortunately it is difficult to grow healthy grapes at home without a routine spray program in addition to good care and a good planting site. Since you are seeing fruit your vine must be doing well. The drying up could be due to a fungal infection, possibly black rot also called mummy grape to which Concord is very susceptible. I would suggest you work with your county extension to develop an annual care program for your grapes. You may also find the following information helpful.
In the meantime, remove any of the bad grapes and dispose of them in the trash, and this fall remove any fallen leaves or other debris and put that in the trash as well. This can help limit the sources of reinfection next year. Good luck with your grapes!
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