Take 1 cup of raisins Rinse the dry grapes in running water well to get rid of the traces of chemicals if any. Soak the raisins in water for 4-5 hours at least or overnight. Alternatively, you can also soak the raisins in hot water for 30 minutes to one hour.
When the raisins are soft enough to mash/grind, transfer to a blender along with soaked water. Grind it to a smooth paste.
Transfer the ground raisins mixture to a strainer over a wide bowl. Press it with a spoon to collect the juice as much as possible. Discard the leftover mix or add it while preparing porridge/jam. But make sure to use the leftovers immediately.
Boil the raisins water in a saucepan until it becomes thick. Keep the flame low to medium and stir it occasionally to avoid burning at the bottom.
Boil until it becomes quite dark, thick, and reached a sauce-like consistency. It may take 15 to 30 minutes at least. Switch off the flame once done.