A Soda and Candy eruption (also known as a Coke and Mentos eruption or a geyser) is a reaction of carbonated beverage and Mentos candies. The numerous small pores on the candy's surface catalyze the release of carbon dioxide (CO2) gas from the soda, resulting in the rapid expulsion of copious amounts of foam.
When the candies come into contact with the liquid, a reaction causes the formation of foam at a rapid rate. A 2006 episode of the television show Mythbusters concluded that the potassium benzoate, aspartame, and CO2 gas contained in the Diet Coke, in combination with the gelatin and gum arabic ingredients of the Mentos, all contribute to formation of the foam.[1] The structure of the Mentos is the most significant cause of the eruption due to nucleation. Mythbusters reported that when fruit-flavored Mentos with a smooth waxy coating were tested in carbonated drink there was hardly a reaction, whereas mint-flavored Mentos (with no such coating) added to carbonated drink formed an energetic eruption, affirming the nucleation-site theory. According to Mythbusters, the surface of the mint Mentos is covered with many small holes that increase the surface area available for reaction (and thus the quantity of reagents exposed to each other at any given time), thereby allowing CO2 bubbles to form with a rapidity and in a quantity that are responsible for the "jet"- or "geyser"-like nature of the effusion.[2] This hypothesis gained further support when rock salt was used as a "jump start" to the reaction.
A paper by Tonya Coffey, a physicist at Appalachian State University in Boone, North Carolina goes into detail on the reasons and physics behind the reaction by stating that it was found that the rough surface also helps the explosion. Coffey found that the aspartame in diet soda lowers the surface tension and causes a bigger reaction, but that caffeine does not accelerate the reaction.[3][4]
A Guinness World Record of 2,865 simultaneous geysers was set on October 17, 2010, in an event organized by Perfetti Van Melle (Philippines) at the SM Mall of Asia Complex, in Manila, Philippines.[5]