Experimenting with Food

April 5th, 2007

I know making geysers by adding Mentos to Diet Coke is soooo 2006, but bear with me for this one. A couple of months ago, I gave a small talk that was sidetracked for 15 minutes while the room discussed the subject. The second-most embarrassing aspect of the story is that I was responsible for leading us into the tangent, and the most embarrassing aspect is that, at one point, I minimized PowerPoint and opened YouTube to show a video of the phenomenon.

I was surprised to learn that many people in the room hadn’t even heard of the experiment. The set up is simple: take a 2 L bottle of your favorite carbonated beverage and several Mentos breath mints. As soon as the mints fall into the liquid, you get an instantaneous violent eruption. The more mints you add, the more violent the explosion. You can check out videos here and here.

From what I understand, there is no chemical reaction taking place—just the physical process of carbon dioxide being outgassed from solution. For some reason, the Mentos brand of mints provide especially nice nucleation sites for the CO2 bubbles to form. I’ve always heard that diet sodas are best for this demonstration because they aren’t sticky (making the clean up easier), but the other solutes (sweeteners, caffeine, etc.) appear to be important, too. These compounds alter the surface tension of the liquid, affecting the solubility of the gas and how quickly it can be released. I understand Mythbusters ran a number of “scientific experiments” on these geysers, but I’d like to see a hardcore experimental physicist get in on the action. It seems like there’s plenty of science left to be done.

In another example of YouTube science, people supercooled bottles of water (or beer) in a freezer and then shock froze the liquids. This involves cooling the liquid below its freezing point, which can be done if you handle the bottle gently enough. When the supercooled liquid is shaken or tapped, it quickly and spectacularly freezes over. I’m told by someone who has studied this phenomenon that it’s unclear what exactly is going on. Maybe the bubbles that are produced from the tapping provide the initial nucleation sites for the crystals to form? It might be similar to the process of selective flocculation used to purify potash salts. In this technique, a surfactant is added to a concentrated solution of the raw mixture of salts extracted from evaporite mines and bubbles are passed into the solution. I’m not sure whether pure crystals form at the air-water interface or if suspended crystals are simply swept along by the bubbles, but the “floc” floats to the top where it is skimmed off and sold. I’d like to see if the shock-freeze experiments work when there’s no air in the bottle, minimizing bubble formation.

Anyway, it seems like there’s a limitless supply of interesting experiments here that could engage high school students and get them to do some real science. It reminds me of the materials chemist who showed that M&Ms pack more efficiently than gumballs. This ground-breaking study merited a Science paper and extensive coverage in the news media (NY Times, CNN, etc.). While you may lament the publication of this paper in such a respected journal, we chemists need to do a better job of engaging the public and convincing them that “chemicals” ≠ “bad”. Undertaking studies involving food and other brand-name products might just help with that.

Previous Comments

  1. Wavefunction Says:
    April 5th, 2007 at 2:08 pm Have you looked at Hubert Alyea’s Tested Demonstrations in Chemistry? The art of demonstration has become extinct. Sloth has engulfed the students, and we need a new bang to start the year with. The coke experiment is bliss, but me, give me a bottle filled with nitrogen triodide and a feather to tickle it with.
  2. Uncle Al Says:
    April 5th, 2007 at 2:26 pm Metastability is hot stuff! Consider diamonds. The US is more than 3 GDPs in debt overall. (One is amazed at how accountancy can render debt as asset). What will trigger phase inversion, whipped cream into grease? When?
  3. aa Says:
    April 5th, 2007 at 4:32 pm When I was 9 or 10, me and my buddy Ian were eating Lik-M-Aids (for those who don’t know remember, these are the candy with two packets of flavoured sugar and a candy stick to eat it with). We decided to colour/flavour our 7-Up by adding the sugar to it. In those bygone YouTube-less days, we had know idea of the force we were about to unleash.

    Orange sugar + 7-Up + white carpet = wet kids + orange carpet + pissed off mother

    Ian’s mum had to move the furniture to cover the stain, but a lifelong fascination with chemistry was born!

  4. Liquidcarbon Says:
    April 5th, 2007 at 4:43 pm This is soooooo earlier than 2006! :)

    Has anyone heard about something you can do with analgin and urea peroxide?

  5. Liquidcarbon Says:
    April 5th, 2007 at 4:47 pm I managed to kill a bottle of champagne this way – forgot it in the freezer. I will never forgive it to myself.
  6. bink Says:
    April 5th, 2007 at 5:59 pm “…Wint-O-Green Life Savers emit faint blue sparks when chewed…”

    You’re kidding?! I totally never knew that…

  7. Uncle Al Says:
    April 5th, 2007 at 6:57 pm Crushing piezoelectric crystals will excite nitrogen, argon, and organic emitters (oil of wintergreen). Dark room, sugar cube, pliers. Bingo. Merely hitting two quartz pebbles together in a dark room will give you flashes. Look up the requirements for piezoelectricity – if is resolved chiral it crystallizes piezoelectric. The reverse need not be true.

    Hmmm… urea inclusion complexes? Explosive plane wave generator, sugar slab, laser dye… one sweet death ray?

  8. Darksyde Says:
    April 5th, 2007 at 7:20 pm I wonder if this works with argon, or nitrogen too. Always wanted to supersat a soda bottle by throwing some liquid n2 inside, then doing the mentos expt. But this requires carful experimentation to properly calibrate the n2 amount (to avoid explosion).
  9. Isaac Says:
    April 5th, 2007 at 8:16 pm Also, Paul, you should know that your former boss had some very nice things to say about you in a presentation he gave at Scripps today.
  10. Wolfie Says:
    April 6th, 2007 at 12:29 am I’m missing Eugene. I fear I chased him away with one of my impertinent comments. Whatever, it’s his own fault, too.
  11. eugene Says:
    April 6th, 2007 at 1:00 am Wow, my own stalker… When you live in Germany, you can’t get one of the natives to give you the time of day, but when you’re on a chem blog, it’s a whole different story.

    Sorry old chap, I’ve been doing some exciting experiments lately and my shit has been working, so I’m taking some extra NMRs and only checking chem blogs three times a day as opposed to the usual number of about ten times a day that always makes me feel like I need to do something better in my off time.

  12. milkshake Says:
    April 6th, 2007 at 1:06 am I hear that the Menthos trick works even better with MnO2 and a big bottle of 50% H2O2…

    triboluminiscence is the word you are looking for

    also, kittens meow when you crush them with pliers (in a dark room)

  13. svejk Says:
    April 6th, 2007 at 2:29 am The use of food-based experiments to illustrate principles in chemistry for school children has a strong track record in France (where else?). Some of this work has been championed by the physical chemist Herve’ This, who holds what may be the world’s only PhD in “Molecular Gastronomy”.
    In addition to his book, some relevant publications include
    This, H. “Molecular gastronomy” Angewandte Chemie Int. Ed. 41: 83-88 (2002) and
    “Food for tomorrow? How the scientific discipline of molecular gastronomy could change the way we eat” EMBO Reports 7: 1062-1066 (2006)
    By the way, he will be giving a talk at the New York Academy of Sciences on April 10.
  14. Mitch Says:
    April 6th, 2007 at 2:38 am So that’s why every other article in phys. lett. is about sand packing.

    Mitch

  15. Paul Says:
    April 6th, 2007 at 3:35 am Isaac: Was the presentation on photoinduced ET? He was and is an absolutely fantastic advisor.

    Isn’t Guinness chocked full of N2 gas? Someone should sacrifice a pint for the good of science, but that might be less humane than sacrificing kittens.

  16. Ψ*Ψ Says:
    April 6th, 2007 at 10:38 am Just leave the poor kittens alone. :,(
  17. Phlogiston Says:
    April 6th, 2007 at 12:04 pm Some of my favorite “food fun” work is Sid Nagel who explained why coffee stains leave a ring, i.e. the “pinning effect”. Inspiration from his breakfast table. Turns out that this has a lot of applications.

    http://physics.uchicago.edu/x_cond.html#Nagel

  18. Isaac Says:
    April 6th, 2007 at 1:53 pm Paul: Yes. He also waxed about Phil, Ke, and the other Paul, who are also here at Scripps. It’s amazing how much good, solid science he’s done mostly with undergrads. I never really thought much about photoelectron buckyball stuff, thought it was mostly fluff until I heard his lecture.

    Phlog: Sid Nagel is totally amazing. Other table stuff include: determining the cone angle of piles of granular material (think a pile of salt but the agro industry is also interested because they tend to pile up stuff like corn kernels), which is basically temperature-independent “thermodynamics”, and figuring out what happens when a string of honey (or hollywood smooch spittle) goes from a hyperboloid of one sheet to a hyperboloid of two sheets.

    I should have worked for him as an undergrad, but I wasn’t a physicist. He also discovered that water drops don’t splash in a vacuum — what’s crazy is all this is stuff that physics should have solved decades ago, but we got obsessed with subatomic and really cold stuff instead.

  19. Herman Blume Says:
    April 7th, 2007 at 12:04 pm Paul,
    Given your apparent penchant for uTube and science, I thought this one was good. No idea where its from though.
    http://www.youtube.com/watch?v=sWE6uPPmgb4

    herman

  20. Wolfie Says:
    April 7th, 2007 at 10:14 pm nice to watch. My nurse is not as frustrated or inhibited, but infortunately she likes to tell me what she thinks.

    i know this is an embarassing comment

  21. Paul Says:
    April 8th, 2007 at 2:04 am Herman, I’ve decided to forego making music videos in lieu of full feature length films. My current projects: Citizen Alkane, Amine Girls, Along Came Polymerization, and Yield of Dreams.
  22. milkshake Says:
    April 8th, 2007 at 6:46 am you forgot “Some like it cold”
  23. The Dude Says:
    April 8th, 2007 at 9:45 pm Personally, I’m trapped in a movie called “Some Degree of Separation”
  24. John Spevacek Says:
    April 9th, 2007 at 9:00 am You can see some triboluminescence in the dark closet if you quickly unroll a few feet of scotch tape.
  25. Everyday Scientist » blog roundup for march/april Says:
    April 10th, 2007 at 11:59 pm […] understanding some strange actions of ordinary food products […]
  26. Everyday Scientist Says:
    April 11th, 2007 at 12:58 am […] understanding some strange actions of ordinary food products […]


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