Rinse kokum with water and soak it in 2 cups of water for 2 hours.
Transfer the soaked kokum along with the water to a blender and blend to make a smooth paste.
Add the kokum paste to a pan along with sugar, the remaining 2 cups of water, cumin powder, ground cardamom, black salt, and black pepper powder. Mix well to combine.
Cook this mixture on medium-low heat for 25-30 minutes, stirring a few times.
Remove the pan from heat and let the mixture cool down to room temperature.
Pass the mixture through a fine-mesh strainer. Press with the back of a spoon to get as much extract as possible. Discard the leftovers.
Store the kokum concentrate in the refrigerator for up to 6 months in a glass bottle. It is also freezer-friendly! You can freeze it for about a year in a freezer-safe zip lock bag or container. Thaw and use whenever required.
To make the sherbet, pour 3 tablespoons of kokum concentrate into a glass and top up with chilled water or club soda.
Note - Shake the concentrate well before using.
Add a few ice cubes to the glass. Garnish with a mint sprig and serve chilled.