Arrange the grapes in a single layer on a tray or in a freezer-safe container, then freeze overnight until completely solid.

When ready to serve, place the frozen grapes, mint leaves, and lemon juice in a food processor. Blend until the mixture becomes crumbly, then continue processing until it forms a smooth, sorbet-like texture. Scrape down the sides of the bowl as needed for even blending.

Serve immediately for a soft consistency, or transfer to a freezer-safe container and freeze for at least 1 hour for a firmer scoopable texture.