Why Do Mentos and Diet Coke React?

Steph B. asks: Why do Diet Coke and Mentos react with each other?

If you’ve ever wondered why Diet Coke and Mentos react so strongly to one another, well, wonder no more.

To start, it should be noted that it’s not just Diet Coke and Mentos that “react”; other carbonated beverages will also readily respond to the addition of Mentos.  What’s going on here is that Mentos has thousands of small pores on its surface disrupting the polar attractions between the water molecules, creating thousands of ideal nucleation sites for the gas molecules in the drink to congregate. In non-sciency terms, basically, this porous surface creates a lot of bubble growth sites, allowing the carbon dioxide bubbles to rapidly form on the surface of the Mentos.  If you use a smooth surfaced Mentos, you won’t get nearly the reaction.

The buoyancy of the bubbles and their growth in size will quickly cause the bubbles to leave the nucleation site and rise to the surface of the soda.  Bubbles will continue to form on the porous surface and the process will repeat, creating a nice foamy result.

In addition to that, the gum arabic / gelatin ingredients of the Mentos, combined with the potassium benzoate, sugar or (potentially) aspartame, in Diet sodas, also help in this process.  In these cases, the ingredients end up lowering the surface tension of the liquid, allowing for even more rapid bubble growth on the porous surface of the Mentos: higher surface tension = more difficult environment for bubbles to form.  (For your reference, compounds like gum arabic that lower surface tension are called “surfactants”).

As to why diet sodas like Diet Coke produce such a bigger reaction, it’s because aspartame lowers the surface tension of the liquid much more than sugar or corn syrup will.  You can also increase the effect by adding more surfactants to the soda before you add the Mentos, like adding a mixture of dishwasher soap and water.

Another factor contributing to the size of the geyser is how rapidly the object causing the foaming sinks in the soda.  The faster it sinks, the faster the reaction can happen, and faster reaction =  bigger geyser; slower reaction may release the same amount of foam overall, but also a much smaller geyser.  This is another reason Mentos works so much better than other similar confectioneries.  Mentos are fairly dense objects and so tend to sink rapidly in the liquid.  If you crush the Mentos, so it doesn’t sink much at all, you won’t get nearly the dramatic reaction.

Yet another factor that can affect the size of the Mentos / Coke geyser is the temperature of the soda itself. The higher the temperature, the bigger the geyser due to gases being less soluble in liquids with a higher temperature.  So, basically, they are more “ready” to escape the liquid, resulting in a faster reaction.

Note that while caffeine is often cited as something that will increase the explosive reaction with the soda, this is not actually the case, at least not given the relatively small amount of caffeine found in a typical 2-liter bottle of soda generally used for these sorts of Diet Coke and Mentos reactions.  If you add enough caffeine, you will see a difference, but the levels required here to see a significant difference are on the order of the amount that would kill you if you actually consumed the beverage. (See: How Much Caffeine Would It Take to Kill You)

You’ll also sometimes read that the acidity of the soda is a major factor in the resulting geyser.  This is not the case either.  In fact, the level of acidity in the Coke before and after the Mentos geyser does not change, negating the possibility of an acid-based reaction (though you can make such an acid based reaction using baking soda).

If you liked this article and the Bonus Facts below, you might also like:

Bonus Facts:

  • While you’ll sometimes hear an urban legend that people have died from drinking Diet Coke and eating Mentos, to date there has not been a single documented instance of this ever happening.  This is likely for two reasons.  First, the act of drinking soda releases quite a bit of the carbonation in it, limiting the possible effect.  Second, even if one did get a strong reaction to eating and drinking Mentos and Diet Coke at the same time, you’d likely just quickly vomit up the foam, which there have been numerous recorded instances of.  On a similar note, birds will not have their stomachs blow up if you feed them dried rice or Alka-Seltzer.
  • As an aside, while I personally have never tried drinking Diet Coke and eating Mentos, I have had a similar experience after taking a new kind of  multivitamin I’d not tried before, combined with drinking a 16 ounce container of Dr. Pepper.  Within a couple minutes of taking the vitamin (after eating and consuming the Dr. Pepper), I noticed I started to feel like I was going to throw up.  I had not at that point thrown up in about 15 years, so this was bizarre.  To keep my streak alive, I attempted, vainly, to keep the contents of my stomach down.  Ultimately, the pressure became too much and I threw up a ton of foam (red, like the multivitamin coating).  It seems likely that the surface of this vitamin must have been porous and it did most likely also contain at the least the gum arabic.  As I had not chewed it before swallowing, it found its way to the still somewhat carbonated liquid (although much less so having drunk it) and produced enough foam to overfill my already somewhat full stomach from dinner.  So let that be a lesson to you.  Certain types of multivitamins and soda also produce a nice foamy reaction.  I’ve also noticed that if you suck off the chocolate of a Snickers bar and then chew it, and swallow, then very quickly afterwards drink some soda, you’ll also get a nice foamy effect in your mouth.  Science!
  • The current world record for the most Mentos / carbonated beverage geysers to be set off simultaneously happened on October 17, 2010 and included 2,865 such geysers.
  • The name “Coca-Cola” was suggested by the creator of Coke, Dr. John Pemberton’s, bookkeeper, Frank Robinson, stemming from the two key ingredients: extracts from the coca leaf and kola nut. Robinson was also the one to first pen the now classic cursive “Coca-Cola” logo.
  • While there were initially different versions of Coca-Cola being sold (depending on the manufacturer, of which there were three primary businesses Pemberton had sold the formula to), all the versions contained cocaine, with some estimates of up to nine milligrams of cocaine per serving.  However, Asa Candler, who eventually finagled exclusive rights to Coca-Cola, claimed that his formulation included only around 1/10th the original formula amount of cocaine and by 1903 he removed cocaine from Coca-Cola by using “spent” coca leaves leftover from the cocaine extraction process.  This still resulted in Coca-Cola having trace amounts of cocaine though.  They’ve since got around this by using cocaine-free coca leaf extract.  The company that prepares this extract, Stepan Company in Maywood, New Jersey, also legally makes cocaine for medicinal purposes.
  • The term “soda-pop” was a moniker given to carbonated beverages due to the fact that people thought the bubbles were produced from soda (sodium bicarbonate), as with certain other products that were popular at that time.  A more correct moniker would have been “carbonated-pop”.
  • The “pop” part of the term came about in the early 19th century, with the first documented reference in 1812 in a letter written by English poet Robert Southey; in this letter he also explains the term’s origin: “Called on A. Harrison and found he was at Carlisle, but that we were expected to supper; excused ourselves on the necessity of eating at the inn; supped there upon trout and roast foul, drank some most admirable cyder, and a new manufactory of a nectar, between soda-water and ginger-beer, and called pop, because ‘pop goes the cork’ when it is drawn, and pop you would go off too, if you drank too much of it.”
  • While in the beginning carbonation was added to drinks because it was thought it was beneficial to the human body, today carbonation is added for very different reasons, namely, taste and shelf life.  Carbonating beverages, introducing CO2 into the drink mix under pressure, makes the drink slightly more acidic (carbonic acid), which serves to sharpen the flavor and produces a slight burning sensation.  It also functions as a preservative, which increase the shelf life of the beverage.
Share the Knowledge! FacebooktwitterredditpinteresttumblrmailFacebooktwitterredditpinteresttumblrmail
Print Friendly, PDF & Email
Enjoy this article? Join over 50,000 Subscribers getting our FREE Daily Knowledge and Weekly Wrap newsletters:

Subscribe Me To:  | 


  • Oh science, always threw the boring out of me, just like art too!

  • In our country(Bhutan), one person has died as a result of drinking coke and eating mentos.. so this is a record.

    • drowning in their own vomit or other function is not a result of the combination of items themselves, anymore than having a car accident that kills, while drinking water or chewing gum is the result of doing so.

      The chemical reaction is not lethal is the “scientific message” but if you combine the two of them inside a space where as the contents overflow (1000 bottles inside a waterproof phone booth that you inhabit as the reaction takes place) the cause of death is not “Mentos and diet Coke” – it is drowning while putting yourself in harms way (or a similar phone booth that permits water in, but not out – and you inhabit it on the beach during a hurricane or tsunami or angry fireman decides to pump water into the booth!).

      “Aspirating vomitus” is a common way to kill rats – as they do not have the valve like most mammals, that switches exposure to the airway. So feeding them Ipacac is not “poisonous” – it just makes them puke. The fact that they weren’t “designed” to puke permits using non-lethal compounds on them – so should scavengers eat them (large birds, cats, etc) they do not die as the often do when arsenic or blood-thinners are used – as they too are consuming lethal doses of the same compound.

      Humans using Ipacac (or just having an upset stomach) along with a ball-gag, or their mouth being taped closed, will certainly cause a drowning in their own vomit – (which is potentially funny, actually! In NY or London, a regular BDSM session with a professional lead to exactly that scenario, and while not at fault, the prostitute went through great pains to hide her presence in a panic, when she wasn’t actually guilty of doing anything other than what her client requested – while he was coming down with a stomach bug of some sort, as was later determined by an autopsy.

      I’m sure many would “Pay Per View” to watch a “Mistress/Master” stuff Donald Trump like a goose, with food — add some ipacac & a leather ball-gag, and then play his video of “pussy” comments – until he vomited. The vomit would be inevitable, due to the ipacac, as would choking upon it and drowning, with the gag in place.

      As a method of raising money for charity, it would net at least a $ 1 billion, and more than a billion laughs!! Add a 3 liter bottle of a no-brand diet soda, with a few drops of other surfactants added, the Mentos, and a secure tube from the bottle into DT’s anus (better make that 9 liters) the abdominal distention would be absolutely hilarious – and likely not lethal, though the fecal vomitus would perhaps have the same result with the ball gag in place.

      You just can’t beat classic humor like that!

      I say use the woman from “The Weakest Link” (UK version) and as assistants, three of the best “Three Stooges” imitators, and YouTube would crash from the traffic – regardless of their data handling capabilities!!

      “Just Say Moe!”

  • This explanation is common across the web but I’m not completely convinced. The reason is that if you simply shake a bottle of soda, the pressure doesn’t change, even though the gas comes out of the bottle. Nucleation sites should not change the pressure, but just increase the amount of gas vs liquid in the bottle, which shaking also does. However, there are videos out there of 100+ mentos in soda bottles EXPLODING the bottles. It seems a bit strange for there to be such an extreme pressure change, enough to explode a bottle.

    Of course, if it is a chemical reaction, then it should be possible to measure the left-over reactants as well as what specifically causes the reaction. I just think something is wrong somewhere.