Remove grapes from stems and place in a colander. Wash thoroughly.
Place grapes in a gallon-size resealable bag.
Pour sugar into the bag and seal. Gently shake the bag to evenly coat grapes with sugar.
Arrange grapes on a paper towel to air-dry any remaining water, about 15 minutes.
Place grapes in a single layer on a shallow pan or baking sheet. Freeze for at least 2 hours.
