Detach all grapes from their stems and rinse thoroughly under cool water using a colander. Allow excess water to drain completely.
Transfer the cleaned grapes into a low, wide container. Pour the sparkling wine and vodka over the grapes, ensuring they are fully submerged in the liquid.
Cover the container with a lid or plastic wrap and place it in the refrigerator. Let the grapes soak for a minimum of 8 hours, or preferably overnight, to absorb the flavors thoroughly.
After soaking, pour the sugar into a flat bowl or plate. Drain the grapes well, but leave them slightly moist so the sugar will adhere.
Working in batches, roll a portion of the damp grapes in the sugar until each grape is evenly coated with a sparkling layer.
Serve right away, or for enhanced texture and flavor, place the sugared grapes back in the fridge for a couple of hours before presentation. These grapes are delightful served in elegant glasses, on party platters, or skewered for stylish snacking.