Continue tasting a grape daily or every other day until the grapes develop the sweet flavor you want. They don't continue to ripen after they're picked, so let them stay on the vine until the taste is right. For some varieties, this could mean tasting the grapes for several weeks, through September and into October.

Grapes picked early in the day, for example, may taste different than those picked in the afternoon. Unlike some other fruits, grapes won't ripen further after you pick them. Monitoring grapes closely is the only way to determine the best time to harvest. As grapes reach maturity, and the cells swell, the fruit gets larger and softer.

Once they have reached the last stage of development, your grapes are ready to be picked and processed. This is the time where you can make your grapes into wine! On average, most grape varieties would ripen 10-20 days after picking them, though this depends on how dry the grapes were after picking them.