This delightful tangy and strong-tasting drink is very popular during hot Indian summers. You can also prepare it a few hours before serving. Chill it and then serve over crushed ice.
Place a shallow pan over medium heat, add the cumin, ajwain, and fennel, and roast for 2 minutes or until fragrant. Let cool and transfer to a spice grinder. Add the black salt and grind to a fine powder.
Pour the black grape juice into a jug; add the ground spices and tamarind pulp and stir well.