Frozen grapes coated in a real sour-and-sweet candy shell, made with citric acid so the sour actually hits.
Citric acid is sold as ‘sour salt’ near canning supplies or spices, and online — don’t substitute lemon juice, it adds moisture and ruins the shell. Sugar-free gelatin powder works fine if you want a lighter version. These are best eaten within 30-45 minutes of coating; the shell softens as the grapes thaw, so keep them frozen until serving.