The scientific mystery behind the explosive reaction produced by adding Mentos to Diet Coke appears to have been solved by students at Appalachian State University.

Through a series of experiments, the students found that a reaction between the rough surface of the Mentos, and the potassium benzoate and aspartame contained in Diet Coke were responsible for the famous geyser reaction, in which the liquid can spew up to 10 feet.

"If you drop a pack of Mentos into a bottle of Diet Coke, you get this huge fountain of spray and Diet Coke foam coming out. This was a good project for my students to study because there was still some mystery to it," New Scientist quoted Tonya Coffey, a physicist at Appalachian State University in Boone, North Carolina, as saying.

There were many theories put forth for explaining the reaction and some bloggers speculated that it is an acid-base reaction because Coke is acidic. In fact, experiments in a 2006 edition of the Discovery Channel programme Mythbusters suggested the chemicals responsible for the reaction are gum arabic and gelatine in the sweets, and caffeine, potassium benzoate and aspartame in the Coke.

However, there were no rigorous scientific studies of the reaction until now. But, Coffey and a team of students tested the reactions between Diet Coke and fruit Mentos, mint Mentos, and various ingredients such as other mints, dish-washing detergent, table salt and sand. They also used other fizzy liquids such as caffeine-free and sugary colas, as well as soda water and tonic water, to compare the reactions.