Wash the grapes thoroughly and pat them dry with a paper towel. Remove them from the stems and place them in a bowl.
Drizzle the lemon or lime juice over the grapes, tossing them gently to ensure they are evenly coated. This helps the gelatin or sugar stick.
Pour the flavored gelatin powder or powdered sugar into a separate bowl. Roll the damp grapes in the powder until fully coated.
Place the coated grapes on a parchment-lined baking sheet in a single layer. Freeze for at least 2 hours or until firm. Serve immediately for a refreshing, candy-like treat.