Typically you will find that grapes can last as long as two weeks if they are properly stored and refrigerated. You will need to take the time to wash your grapes off before putting them in the fridge though, just to make sure that all of the pesticides are completely gone.

Since you do not know which chemicals if any were used in the growing process, it will be crucial to do this. As long as you keep your grapes in a proper place inside your refrigerator (the crisper is best), you shouldn’t have any problems with keeping them from rotting for a week to two weeks.