Like natural seedless raisins, these are Thompson Seedless grapes, but are oven-dried to avoid the darkening effect of sunlight. They are also treated with sulfur dioxide to preserve the light color. The best seedless green grapes quickly dried to keep their golden color and fine flavor. Storage: Unopened packages of raisins will keep almost indefinitely in the refrigerator. Once opened, reseal the package, excluding as much air as possible, or transfer the raisins to an airtight jar or bag. Proper storage will deter the fruit from drying out and will prevent the sugar from crystallizing on the surface. If refrigerated, the raisins will keep for up to a year; they will stay even longer in the freezer and they will thaw quickly at room temperature.