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A Diet Coke and Mentos eruption (alternately Diet Coke and Mentos geyser or Mentos eruption) is a reaction between the carbonated beverage Coca Cola's Diet Coke and Mentos candies that causes the beverage to spray out of its container. The gas released by the candies push all of the liquid up and out of the bottle for a huge explosion. Lee Marek and "Marek's Kid Scientists" were the first to demonstrate the experiment on television in 1999. Steve Spangler's televised demonstration of the eruption in 2005 went viral on YouTube, launching a chain of several other Diet Coke and Mentos experiment viral videos.
In the 1980s, Wintergreen Lifesavers were used to create soda geysers. The rolls of candies was threaded onto a pipe cleaner and dropped into the soda to create a geyser. At the end of the 1990s the manufacturer of Wintergreen Lifesavers increased the size of the mints and they no longer fit in the mouth of soda bottles. Science teachers found that Mint Mentos candies had the same effect when dropped into a soda bottle.
Lee Marek and "Marek's Kid Scientists" performed the Diet Coke and Mentos experiment on the Late Show with David Letterman in 1999. In March 2002, Steve Spangler, a science educator, did the demonstration on KUSA-TV, an NBC affiliate, in Denver, Colorado. The Mentos Geyser Experiment became an internet sensation in September 2005. The experiment became a subject of the television show Mythbusters in 2006. Spangler signed a licensing agreement with Perfetti Van Melle, the maker of Mentos, after inventing an apparatus aimed to make it easier to drop the Mentos into the bottle and produce a large soda geyser. Be Amazing Toys, Spangler's toy company, released the Geyser Tube toys in February 2007. In October 2010, a Guinness World Record of 2,865 simultaneous geysers was set at an event organized by Perfetti Van Melle at the SM Mall of Asia Complex, in Manila, Philippines.
The structure of Mentos is a significant cause of the eruption because of its nucleation sites. 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 carbon dioxide bubbles to form with the rapidity and quantity necessary for the "jet"- or "geyser"- or eruption like nature of the effusion. This hypothesis gained further support when rock salt was used as a "jump start" to the reaction. Tonya Coffey, a physicist at Appalachian State University in Boone, North Carolina, confirmed that the rough surface of the Mentos candy helps speed the reaction. Coffey also found that the aspartame in diet soda lowers the surface tension and causes a bigger reaction, but that caffeine does not accelerate the reaction. The geyser reaction will work using regular or diet soda, although diet is commonly used to avoid having to clean up a sugary soda mess.
Once the mint candies are added to the beverage, bubbles form around the surface of the candy and rise to the surface of the liquid. In addition to the gas released by the Mentos, the weight of the mints sinks them to the bottom of the bottle. These two factors combined create the soda blast.
The potassium benzoate, aspartame, and carbon dioxide gas contained in Diet Coke, in combination with the gelatin and gum arabic ingredients of the Mentos contribute to the formation of the foam.