Place grapes and champagne into a bowl to cover the grapes.
Soak the grapes for at least 12 hours.
Drain grapes.
Place sugar in a bowl or bag and toss grapes with the sugar until fully coated.
Transfer to an airtight container and freeze for two hours.
Notes
These grapes are best served frozen.
In an airtight container, you can store the grapes at room temperature for 24 hours, in the fridge for up to 4 days, or in the freezer for up to a month.