Coke & Mento Geysers: How?


We’ve all seen it – drop a mint mento into a bottle of Diet Coke and it creates the most incredible eruptions of foam. But what is the science behind it?

geyser

It is mainly due to ‘nucleation’.  This is when the carbon dioxide in the Coke is attracted to the Mentos. The pressure created then sends the Coke bubbles soaring into orbit (or something like that)…

Nucleation is deemed by scientists as a physical reaction, not a chemical reaction. The carbon dioxide is squeezed into the drink to make it fizzy, and since it is trying to escape, it is pulled towards any lumps – the Mentos, in this case.

Nucleation can happen on anything – shards of glass, specks of dust etc. However, Mentos work well because each individual sweet is covered with over 30 layers of sugar (don’t tell your dentist), so that provides many nucleation sites for bubbles to form. Mentos then sink, so all the carbon dioxide is attracted and forms bubbles in all the little gaps all the way to the bottom. The bubbles turn to foam, and the pressure becomes too much for the bottom to handle…

nucleation

But there are, as in any scientific idea, some questions. Why does it have to be Diet Coke? Well, it doesn’t have to, but Diet Coke is less sugary than normal Coke, so when the geyser is formed, the goo won’t be all sugary when it splatters all over you. Also, the sweeteners add to the pressure in the drink.

And what else works? In fact, if you drop anything into a fizzy drink it fizzes a little, but the Mento & Coke combo is very effective!

One more thing – what will happen if you drink Coke and then eat Mentos? It certainly won’t be pleasant, but it probably won’t cause you to splurge out geysers all over the place. This is due to a number of things – firstly, the majority of the fizz goes away as you drink. When the bubbles are formed in your stomach, it expands slightly. Your stomach won’t explode, as it is quite skilled in the art of… erm, releasing gas. Despite this, it wouldn’t be any fun, so stick to nucleation in your back garden for now!

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