Sunday, November 6, 2011

Why Do We Cry When We Cut Onions?

I hate cutting onions. 

But it is one of the most essential ingredients for good food, so I rarely let my eyes stop crying.

When we cut open an onion, we allow an enzyme called alliinases to react and break down amino acid to generate sulphenic acid. At this point the chemical still remains on the cutting board-- so how does it get to our eyes?
A second enzyme called lachrymatory factor synthase or LFS later mix with sulphenic acid to form, get ready for this, propanethiol S-oxide. Propanethiol S-oxide is a volatile gas, and it travels readily in the air. When the gas reaches your eyes, it mixes with water in your eyes to form sulfuric acid. This prompts our eyes to release water to irrigate the irritating invader.

The natural reaction to the Propanethiol S-oxide invasion is to shut your eyes. This, of course, is not a good idea if you are cutting an onion. Rubbing your eyes is a bad idea, since your hands are likely full of the tear-making onion juice, and by rubbing your eyes you are actually transferring the sulphenic acid to your eyes, in addition to the sulfuric acid induced by the Propanethiol S-oxide gas.
So how do you keep from crying? I believe there are many methods out there, or some traditional methods passed down from mom to child, but I need luck finding them.
Otherwise, I'll stick to wearing goggles.


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