Does rinsing grapes before storing them cause them to spoil more quickly?
To find out, we took bunches of red and white grapes and removed any on-the-verge or obviously rotten ones. Then we rinsed and dried half of each bunch, leaving the other half unrinsed. We also wondered if leaving the fruit on the stem hastens or delays spoilage, so we plucked some of the grapes from their stems and left the remaining clusters intact. Then we refrigerated all the samples in the perforated bags that we bought them in.
All of the rinsed grapes spoiled within just a couple of days. Why? Even though we had dried them as much as possible, moisture exposure encouraged bacterial growth. The unrinsed loose grapes were the next to rot, as the now-exposed stem attachment point became an entryway for bacteria. Unrinsed stem-on grapes fared best, lasting nearly two weeks before starting to decay. In fact, as long as we periodically inspected the bunches and removed any decaying grapes, most of them—both red and white samples—kept for an entire month.
In sum: Don’t pull grapes from their stems before refrigeration. Simply discard any that show signs of rotting and hold off on rinsing until just before serving.