Cola and Mentos experiment. Computer illustration showing the fountain of foam that is produced when mint Mentos sweets are dropped into a bottle of cola. The potassium benzoate, aspartame, and CO2 gas contained in the cola, in combination with the gelatin and gum arabic ingredients of the Mentos, all contribute to the formation of the foam. However, the rough texture of the sweets' outer surface helps speed the reaction and the sudden increase in pressure pushes the foam out the top of the bottle, producing a foam fountain.