Chop tomatoes discarding stems and pressure cook upto 2 whistles with little water and salt.Cool and blend in a blender.Strain the pulp in a strainer.Discard seeds and residue.

Boil the pulp with food colour, sodium benzoate and 1 tsp vinegar. Food colour may be replaced with a slice of boiled beetroot while boiling tomatoes. Cool and store in a bottle and refrigerate.