Fueling the Mentos and Diet Coke Explosion

Interest in Mentos and Diet Coke has exploded over the past year. Chances are you have probably seen the Mentos and Diet Coke videos on YouTube= or Google Video. When a roll of Mentos is dropped into a 2 liter of soda it forms an instant geyser—sometimes as high as 20 feet. What started as a backyard experiment has spread through viral video and recently received significant media coverage from a variety of outlets including NPR, the Today Show, and Letterman. This week, MythBusters set out to understand the science behind the explosion.

As explained by the Mythbusters, Adam Savage and Jamie Hyneman, "Basically the Mentos start to dissolve, and it’s like tripping a switch…it’s a cascade whereon all of a sudden, all of the CO2 that was contained in the liquid is suddenly not as attracted to the liquid as it was before, because of this slight change in the chemistry that occurs." At rest, the carbon dioxide molecules in the soda are held together by water molecules. The Mentos have tiny pits, or nucleation sites, that provide locations for the carbon dioxide molecules to form. In addition, the gelatin and gum aribic in the Mentos breaks the surface tension making it easier for bubbles to form. Although Mentos has the spotlight, it appears salt may do the trick as well. According to Hyneman, "Plain old table salt is better." Richard Zare from Stanford agrees.

Mentos hopes this cheap alternative doesn’t catch on. They estimate the advertising value of this craze has already topped $10 million dollars. Much of this has been driven by eepybird.com. Eepybird’s video, which features 200 liters of Diet Coke and 500 Mentos, has been downloaded over 6 million times. To keep the craze alive, Mentos just announced a contest for the best geyser judged on creativity/uniqueness (50%), execution (25%), and production quality (25%). The winner walks away with 1,000 iTunes and a year’s supply of Mentos. Coke, on the other hand, discounts the free publicity, "we would hope people want to drink [Diet Coke] more than try experiments with it."