A Diet Coke and Mentos eruption, Also known as a Mentos eruption or a coke geyser is a reaction of Diet Coke and mint Mentos candies. A two-liter bottle of Diet Coke or of another carbonated beverage is used. Diet Coke is preferred because it tends to react better. Dropping some Mentos into the bottle, usually around four, causes the Diet Coke to foam at a rapid rate and spew into the air. Mint-flavored Mentos are used, as fruit-flavored Mentos have a smooth coating which slows the reaction. Because of the spectacular nature of this physical reaction and the easy availability of the ingredients, the eruption is a popular subject for Internet videos, also appearing in non-Internet sources.
A variation of this experiment consists of making the bottle rocket up by closing the cap shortly after Mentos is inserted and then slamming the bottle into the ground cap first. The explosion will generate a reaction like a rocket.
Steve Spangler initiated the Internet phenomenon when he appeared on 9News in 2002 and 2005, both times showcasing the experiment. The experiment's result was then further popularized by the website Eepybird.com, which promoted a video in which Fritz Grobe and Stephen Voltz re-created the fountain display seen in front of the Bellagio hotel in Las Vegas using a timed series of eruptions. Later Eepybird videos featured "self-activating" soda jets linked together to form a Domino Rally-style effect. In September 2007, the videos, including the "Extreme Diet Coke and Mentos Experiments" video that was viewed more than 10 million times, earned the pair the highest yearly payout of US$50,000 from the video hosting service Revver.
The eruption has been reproduced many times by popular sources, including the television shows Numb3rs, Bones, and Ellen DeGeneres and an appearance by cast member Kari Byron in FHM magazine, an experiment conducted by Bart Simpson on The Simpsons episode, "The Debarted", an appearance on the Late Show with David Letterman by physics teacher Lee Marek, and others. The MythBusters later set the record highest soda jet recorded, at over 29 feet (9 meters), using a nozzle.
Setting world records for the most simultaneous Mentos-and-Diet-Coke Eruptions has become a new challenge for many groups of people. The original world record - 504 simultaneous eruptions - was set on May 24, 2007, and was broken on July 10, 2007, by Circle R Ranch and Books Are Fun during a special event in Flower Mound, Texas. Guinness World Records certified the record-setting effort when independent sales representatives from Books Are Fun, a Reader's Digest Company, simultaneously dropped Mentos into individual two-litre bottles of Diet Pepsi, creating 791 geysers and reaching over 32 feet with the use of a nozzle.
The next record was set on April 23, 2008, by students of Ekonomika, the fraternity for students studying Economics, in the Belgian city of Leuven; they simultaneously launched 1,360 Mentos geysers. Then, on May 14, 2008, students at Louisville Male High School in Louisville, Kentucky, broke that record by setting off 1,800 simultaneous geysers.
The current Guinness World Record—1,911 simultaneous geysers—was set on June 19, 2008, by students of the School of Business Administration Turiba in Latvia. This record was registered by the official representative of the Guinness World Record book. j
In a 2006 episode of MythBusters, a popular television program on the Discovery Channel, the MythBusters concluded that the caffeine, potassium benzoate, aspartame, and CO2 gas contained in the Diet Coke and the gelatin and gum arabic ingredients of the Mentos all contribute to the jet effect. In addition, the MythBusters theorized that the physical structure of the Mentos is the most significant cause of the eruption due to nucleation. When flavored Mentos with a smooth waxy coating were tested in carbonated drink, the reaction occurs only mildly, where as standard Mentos added to carbonated drink formed an energetic eruption, by their claim, affirming the nucleation-site theory. According to the MythBusters, the surface of the mint Mentos is littered with many small holes, allowing CO2 bubbles to form very rapidly and in great quantity, in turn causing the jet of foam. This was further supported when rock salt was used as an effective substitute for Mentos.
Steve Spangler first put the Mentos Geyser in the public eye, has several videos and detailed experiments about it on his website. The Geyser Tube is a device invented for use in creating the reaction.
One reason for the popularity of the eruption is its comparative safety. Because the interaction releases only the small amount of carbon dioxide present in the liquid, the cola bottle should not usually rupture if capped—although it is possible to break the bottle with physical force. This differs from similar demonstrations with a dry ice bomb which has the potential to generate much larger pressures depending on the amount used. The MythBusters also noted when testing the experiment that, unlike other materials such as dry ice which are relatively expensive and rare, Diet Coke and Mentos can be acquired at almost any local shop in countries where Mentos are sold. Many high school or middle school science labs experiments are based on this phenomenon, as it can promote a better understanding of chemical or physical reactions.