To check watermelon adulteration with erythrosine, a synthetic red food dye, FSSAI recommends performing a test. "Cut the watermelon in half, take a cotton ball and rub it in the inner succulent parts of the watermelon," says FSSAI. The cotton ball rubbed on the unadulterated watermelon does not change colour while the cotton ball rubbed on adulterated watermelon turns red.