The 'MythBusters' Take on the Mentos/Diet Coke Craze

If you go to the viral video site YouTube.com and search for "Mentos Diet Coke," you'll come up with many videos, going back months, that show people dropping mint Mentos candies into bottles of Diet Coke and watching the immediate shooting geyser that results.

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Sure, it's fun to do and cool to see, but there has to be some science behind it. Enter Discovery Channel's "MythBusters," two guys in San Francisco -- Adam Savage and Jamie Hyneman -- who put urban myths, commonly held beliefs and tall tales to the test.

In a new episode airing Wednesday, Aug. 9, at 9 p.m., "MythBusters" takes on the worldwide craze for erupting soda bottles.

According to Hyneman (he's the mustachioed MythBuster), it's a process called "nucleation," in which the particular chemistry of the Mentos candy interacts with the chemistry of the carbonated Diet Coke, causing the carbon dioxide gas, or CO2, to suddenly come out of suspension in the liquid and make a break for freedom.

But you have to have the right Mentos.

"The non-mint type," Hyneman says, "have a glaze on them, and they don't work at all. It only works with the mint ones, because they have a matte finish. That surface serves as these little portals for the gas to escape through."

But the story doesn't end there.

Hyneman says, "There's a cascade that happens with -- it's a little esoteric -- an ion exchange. Basically the Mentos start to dissolve, and it's like tripping a switch. It's not what you would call a chain reaction, because that's something else in chemistry terms, but 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."

That's not surprising, since we all know how a change in chemistry can cause attraction to wane. But as in many things, a little sweetness can slow the process -- so regular, sugared soda doesn't produce the same reaction.

"Sugar molecules are very large," Hyneman says, "and that doesn't allow this to happen as quickly. That's the key. Sugar is gooey and sticky -- even though it doesn't seem that way when it's in a soda, but there's a lot in there -- and it helps hold onto the CO2 a lot better."

On the other hand, Hyneman says, sweetness of no kind -- natural or artificial -- results in a disappointing fizzle.

"In the case of just plain seltzer water," he says, "which we also tried, that doesn't work, because the CO2 already wants to come out."

Mentos, though, isn't the only thing that can make a satisfying diet-soda geyser.

"Mentos," Hyneman says, "which is all well and good, and it works quite well, is actually not the best performer in creating this eruption. Plain old table salt is better."

Hyneman also says it isn't necessary to use Diet Coke, that any artificially sweetened carbonated soda should work well. However, he doesn't recommend chugging diet soda and then popping Mentos.

"That's something I was actually concerned about," he says. "I took a big swing and popped a couple of Mentos in my mouth, and the soda pretty much came out my nose and sprayed all over the place. Everyone laughed. I've got this big mustache -- it's kind of my trademark on the show -- and it was dripping all over off this mustache and made a big mess.

"Just drink the soda and enjoy it, and then eat the candy some other time."

The experiment has had one lasting effect on the "MythBusters" team.

"We've had cases of Mentos around," Hyneman says. "We're kind of addicted to them. They're hanging out on the tables while we're running around, doing our experiments. They're quite tasty, yeah."