3/4 cup thawed frozen unsweetened tamarind purée
2 cups water
3/4 cup sugar, or to taste
2 1/2 cups diced fresh mangoes (from 2 large)
1 (750-ml) bottle chilled dry white wine
1/3 cup tequila (preferably reposado)
1 cup halved green and red seedless grapes
Purée tamarind, water, sugar, and 1 1/2 cups mangoes in a blender until mixture is smooth.
Pour through a medium-mesh sieve into a pitcher and stir in wine, tequila, grapes, and remaining cup mangoes.
Chill, covered, until ready to serve, up to 24 hours. Serve over ice.
Makes 10 to 12 drinks.