Hello allicin!

So as everyone knows, chopping onions makes you cry. I’ve seen people chop onions wearing swimming goggles to try and prevent tears and, interestingly, this can actually work. But not necessarily for the reason you think. Allow me to explain…

Onions, like most plants in the family Alliaceae produce a compound called allicin. It’s the compound responsible for the characteristic pungent smell of raw onions. This chemical is also the plant’s primary defense mechanism. It’s antibacterial, antifungal and repels pests. The thing is though, allicin is only formed in large quantities when onions are damaged — by a chef’s knife, for instance.

When you cut an onion, enzymes rapidly generate allicin. After creating allicin, more enzymes break it down into sulfenic acids. These sulfenic acids are extremely volatile, so they get carried away as vapour. They’re also quite unstable, and will rapidly convert to sulfuric acid on contact with water.

Onions make you cry because while chopping them, you inhale this onion vapour. When sulfenic acids come into contact with your tear ducts, they react and turn into sulfuric acid. It’s this weak sulfuric acid solution in your tear ducts that causes the tears and stinging sensation while chopping onions.

So just covering your eyes isn’t actually enough. Wearing goggles can work, because they can also pinch your nose and close off your tear ducts. A much easier solution though, is to simply take a step back while chopping onions, breathe through your mouth and never ever lean over the chopping board while you’re chopping.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
This entry was posted in chemistry, Imported from Livejournal, molecular gastronomy and tagged . Bookmark the permalink.

15 Responses to Hello allicin!

  1. madsophia says:

    I have some, it’s pretty good:)

  2. invaderxan says:

    Wow… I didn’t know that! Thanks! :)

  3. invaderxan says:

    Heheh… They’re evil, and that’s why they’re good.
    Personally, I prefer red onions. They’re sweeter, milder and have a nicer flavour…

  4. invaderxan says:

    Sounds perfectly fair to me. :)
    Mind you, I enjoy food that bites back… Hence my love of chillis.

  5. invaderxan says:


  6. invaderxan says:

    It’s probably something fairly trivial like how you stand, y’know… I always used to wonder why onions sometimes affected me and other times didn’t.
    In fairness, it’s a bad habit to lean over a chopping board, anyway…

  7. davidnm says:

    That really doesn’t sound good, does it?

  8. davidnm says:

    Weirdly, I don’t seem to be much bothered by onions. I’ve no idea why that might be, though.

  9. Heh, actually, I don’t like the taste of onion. :-) But, the fact that they can fight back just gives me even more reason to dislike them.

  10. madsophia says:

    this is awesome. damned evil onions, but I love them so!

  11. madsophia says:

    maybe you should try asafoetida. it can be substituted for the flavor of onion and is used widely in parts of India where certain practices prohibit the eating of root vegetables.

  12. I never eat or chop onions. Any vegetable that can fight back against being cut deserves not to be eaten. ;-)

  13. Neat! I didn’t know all that.

  14. invaderxan says:

    The… onion guy?

  15. Anonymous says:

    Brings back bad memories of being low man on the totem pole at Quizno’s, and being forced to be the onion guy.

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