Grapes do not ripen after harvesting, so look for grapes that are well colored, plump, firmly attached to the stem, and wrinkle-free. After purchase, grapes should be stored in the refrigerator, where they will maintain their freshness for several days.
While freezing detracts from their flavor, frozen grapes are a wonderful snack that kids really enjoy. To freeze grapes, wash and pat them dry, then arrange them in a single layer on a cookie sheet and place in the freezer. Once frozen, transfer them to a heavy plastic bag and return them to the freezer, where they will store for up to six months.