On November 15th of last year, 4,334 people gathered at the Festival Internacional del Globo in Mexico with two-liters bottles of soda and packets of Mentos in hand. Then, like some grand science class demonstration, they set the Guinness World Record for most simultaneous Mentos and soda fountains.

Dropping some Mentos into soda for the resulting bubble cascade has been a staple science demo for years, probably reaching a cultural tipping point with the MythBusters‘ episode testing the phenomenon. The reason? It’s cheap, easy, safe, and spectacular. Just look at how much fun this is:

The reason why hard candies cause such a reaction when dropped into soda is more complicated than you’d think, but the driving force behind the fountain is a massive, immediate release of the soda’s carbon dioxide.

When soda is made, it’s bottled under high pressure carbon dioxide gas. Much of that gas dissolves into the liquid, but it is supersaturated — there is more gas in the soda than there normally would be at atmospheric pressure. Popping off the cap releases that excess gas, and the rest of the carbon dioxide slowly bubbles out of the drink until equilibrium is reached.

What dropping a Mentos into that fizzy solution does is provide what are called “nucleation sites” for bubbles to form. Normally, the tension between water molecules makes it hard for bubbles to well, bubble. However, give the gas molecules somewhere to gather — the cracks and crevices of a hard candy — and the bubbles can form easily and rapidly.

The Mentos just happen to be very good sources of nucleation sites for very fizzy soda. Oh, and by the way, I’d also like to see the world record for most Mentos on a dunk suit too (but not in a bathtub).

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IMAGES: Gonzalo VP; WOB GoPro