Mentos surface structure. Computer illustration showing the rough structure of the outer surface of a mint Mentos sweet. When mint Mentos are dropped into a bottle of cola a fountain of foam is produced. 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, it is this rough texture of the sweets' outer surface that helps speed the reaction, leading to a sudden increase in pressure, which pushes the foam out the top of the bottle, producing a foam fountain.