Put Next to Water, an Onion's Not So Hostile

By Andreas Viestad
Special to The Washington Post
Wednesday, October 8, 2008

I can walk through a room so thick with smoke that you can cut bricks out of it, and I won't blink. But if I ever need a good cry, I know just what to do. I need only look at an onion before tears start welling. The first cut has me reaching for my handkerchief.

Onions have the same effect on me that romantic B-movies do: My eyes water even though I am not really sad.

Over the years, people have given me varied advice on how to prevent crying when cutting onions. One of the more eccentric involves clenching a wooden spatula or a piece of toast between my teeth. That makes it hard to talk -- so it prevents me from complaining -- but it seems to have little effect on my eyes. Martha Stewart once told me to keep a candle burning next to the place where I am chopping. It is a lovely touch from the Queen of Cozy, but unfortunately it is no more effective than the spatula. Others have told me to chop in a plastic bag, chop really fast or stick a burnt match up my nose.

Swimming goggles were long my preferred defense. But although they protected my eyes, they had the significant disadvantage of impairing vision, which is not recommended when playing around with knives. After parting with a fingertip, I returned the goggles to the closet, next to my flippers and swim trunks, where they belong.

I have had more use for a piece of advice once imparted to me by legendary bluesman Screamin' Jay Hawkins, who said, "You know, you can't be an idiot all your life!" Better to be the grown man crying than the sad and ridiculous figure in the candlelit kitchen with a wooden spatula in my mouth and a match up my nose, chopping onions inside a plastic bag.

Whence comes this tragedy that manifests itself in my eyes? I have known for years that cutting onions makes me cry. But I had no idea why, apart from the fact that the onion contains some nasty compounds.

Luckily, there are those who know. One of them is chemistry professor Eric Block at the University of Albany, who is writing a monograph on the folklore and science of allium plants (which include garlic, onions and leeks) for the United Kingdom's Royal Society of Chemistry. Some years back, Block and his co-workers isolated the tear-inducing ingredient in the onion and characterized it as propanethial S-oxide, a light and volatile chemical that is also water-soluble. Block describes the tear-inducing, or lachrymatory, effect as the onion plant's attempt at "a type of chemical warfare."

"This is very commonly exhibited by plants, who obviously cannot run away from predators," Block says. "So they stand and fight as best they can, sometimes reducing their attackers to tears."

Most advice on how to prevent onion-related crying is, Block says, "poppycock."

"Don't believe everything Martha Stewart says," he cautions.

So what does work? Block does not claim to have discovered the perfect solution to the problem, which is not the main focus of his research. But he insists that the best way to find an adequate answer is to think like a detective.

"You have got to study the perpetrator and what drives him," Block says. "In this case we have a very volatile substance that is water-soluble. See?"

The onion's attack is not targeted or personal, although it certainly feels that way. The lachrymator acts as a lachrymator only when it reaches my eyes; if it encounters another source of water first, it will discreetly dissolve there.

A little understanding of science helps with the detective work. And those traditional remedies provide clues. Keeping a wooden spatula in your mouth when cutting onions makes you look stupid, and it does not really work. But it does expose your tongue and the wet environment in your mouth, so in a minor way it is attempting to divert the lachrymator.

Knowing that can help me fight the perpetrator. How? If it is the water in my eyes the onion is after, then I'll give it more water. One of the few proven ways to avoid the crying game is to cut the onions under water, running or otherwise. It is as close as you can get to a foolproof technique, and it works even on my super-sensitive eyes. The water literally washes away the cause of all my tears.

The problem, of course, is that working underwater is almost as impractical and dangerous as wearing goggles. It also gets rid of the sugars that caramelize during cooking and lend that wonderful sweetness, plus all the non-lachrymatory sulfurous compounds that make the flavor of onions not only pungent but also interesting and complex.

I go for a moderated application of the principle: chopping onions next to running water, on a wet cutting board. With so much water around, much less of the offensive substance reaches my eyes. Food scientist Harold McGee suggests cooling onions in ice water for a few minutes before cutting them. That slows down the speed of the lachrymator and reduces its volatility.

Stewart's lovely touch with the candle also points us toward a solution. The burning flame creates a convection effect, stirring the air and leading the lachrymator away. In a more enlightened and electrified kitchen, that can be achieved to much better effect by turning on the exhaust fan.

It is also worth remembering that the onion consists of cells, and only when those cells are ruptured are the compounds released into the air in a significant quantity. A dull knife will bruise and fracture a large number of cells.

A sharp knife will give you more precision and rupture fewer cells. It is also a necessity if you are going to make Michel Richard's ingenious onion-based pasta-free "carbonara" (see recipe for Low Carb-o-Nara.) Richard plays with the texture of the vegetable: When the onion is very finely sliced, then steamed or boiled so that the strong flavor is removed, you can almost mistake it for pasta.

It's a trick that will make you chuckle, not cry.

Andreas Viestad, author of "Where Flavor Was Born" and co-host of the upcoming public television series "Perfect Day," can be reached at http://www.andreasviestad.com or food@washpost.com. His Gastronomer column appears monthly.

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