You may like them on your hamburger or in your soup, but onions
can be kind of a pain to prepare. We’ve all been there while cutting an onion -- your eyes sting and then run with tears, sometimes your nose even stuffs up.
The pain can be unbearable and none of the internet remedies you research seem to
work. Why does this always happen with an innocent-looking vegetable, no less?
Obviously, there’s something in onions that makes you cry. In fact, it's a pretty powerful chemical irritant called syn-propanethial-S-oxide. When
cut, the onion releases lachrymatory-factor synthase, which converts the amino
acids sulfoxides of the onion into sulfenic acid. The acid rearranges itself
into syn-propanethial-S-oxide, a volatile chemical that turns into vapor. When
the vapor hits your eyes, it irritates the
lachrymal glands so that they produce tears.
Your eyes aren’t overreacting to this chemical, either. The powerful vapor has the
same effect as very painful tear gas. Onions pose no long-term threat, however, and pain
peaks in about 30 seconds. The whole event is over within five minutes when the
enzymes have all escaped, stopping the chemical reaction.
The sulfur in your onions is not only part of the chain of
their self-defense, but it also gives the onion its pungent flavor. The onion pulls sulfur from the ground as it grows. If you grow
the onion in low-sulfur soil, you get a milder onion like a Vidalia onion; sweeter taste, less crying, but less flavor when you are cooking them.
But back to the tissue issue -- how do we stop this complex chemistry from descending upon
our eyeballs and making us weep? Freezing and refrigerating onions slows down the enzymes and the
resulting chemical chain reaction. Giving a peeled onion a quick soak also helps,
though it rinses away that valuable sulfur flavor. Goggles that act as a
barrier to the onions are the most obvious and best choice to keep the tears at
bay. Other techniques, like holding bread in your mouth or lighting a match?
Not so effective.
So don’t feel bad the next time you get bested by an onion -- it’s a losing battle for humans versus alliums every time. Take solace in the fact that even when you lose the battle, you ultimately win the war with every
bite. Take that, onion.
Your breath after you eat one, however, is an entirely different story...