Today's bit of odd but potentially useful information.
The Tear Factor
By Robert L. Wolke
Wednesday, August 21, 2002; Page F01
I've read many hints about how to cut onions without crying, but none of them seems to work. Is there some trick that I can use, short of always buying sweet, or "no tears" onions, which don't have the same pizazz as ordinary ones?
What makes me cry is all the misinformation going around about onions, primarily about what causes the eye irritation and how sweet onions differ from ordinary ones.
The tear- producing chemical (the lachrymator) in onions is not pyruvic acid, as was recently asserted by an eminent house and garden guru in her eponymous magazine and promulgated in the food section of a major East Coast metropolitan newspaper. (The erroneous magazine statements did not appear under the guru's personal byline. You think she writes that whole thing herself?) Nor does pyruvic acid "come from sulfur in the soil" as the magazine asserts, because pyruvic acid contains no sulfur. Nor does the lachrymator consist of sulfonic or sulfurous acid, as contended in a recently published food book. Indeed, it is not an acid at all. It is a sulfur-containing compound called Thiopropanal S-oxide. While knowledge of that fact isn't going to change your life, the record has long been in dire need of being set straight. So there.
The Sting
Thiopropanal S-oxide (from here on, I'll call it compound T for "tearjerker") does not exist in onions as such; it is formed when the onion is cut or crushed, which breaks open its cells and releases two chemicals that until then had been isolated from each other: the enzyme alliinase (compound A), and a form of alliin (found in onions, garlic and similar plants) familiarly known to chemists by its nickname S-(1-propenyl)-L-cysteine sulfoxide (compound B). These two chemicals react with each other instantly to form the tear gas: A + B T. As this volatile compound evaporates and reaches your eyes, it dissolves in the tear layer on the corneas and a small part of it turns into sulfuric acid -- battery acid -- which, as you might expect, produces a burning sensation. At the same time, the tear glands are activated in an attempt to wash the irritant away, just as when you get something in your eye.
It would be nice to think that there is a single chemical in onions that both irritates our eyes and gives us the flavor effect of pungency, a hot, sharp and stinging sensation in the mouth. But these effects are largely due to two different compounds. The tear gas compound T is not primarily responsible for the onion's pungency, as is commonly stated in the popular food literature. The most pungent onions are not necessarily the most notorious tearjerkers.
An article by Dr. Bill B. Dean of Washington State University in the May-June 1999 issue of Onion World points out that the overall flavor of onions has at least four components: the tear gas compound, certain pungency compounds, sugars and miscellaneous flavor compounds. Like the tear gas, the main pungency compound develops only after the vegetable's cells are broken open by chewing, whereupon the enzyme alliinase (A) and the chemical S-alk(en)yl cysteine sulfoxide (compound S) react with each other to produce pyruvic acid + ammonia + sulfenic acids, which in turn produce other flavor compounds. The amount of pyruvic acid formed in this reaction is generally taken as an index of pungency, but only because it is stable and easy to measure in the laboratory. It is not itself responsible for the pungency of onions.
Now what about those sweet onions, such as the Vidalia, Maui, Walla Walla, Texas 1015 and OSO? Forget the word "sweet." They should really be called milder or less-pungent onions, because they don't necessarily contain more sugar than others; they simply contain lesser amounts of the pungent compounds.
Ultimately, I must forgive Ms. Eminent House and Garden Guru for allowing her magazine to say that pyruvic acid is "the substance that makes people cry when they cut onions." She probably obtained that bit of misinformation from the Web
site of the sweet onion
producers themselves (www.sweetonionsource.com), where I also saw it. She was merely trading on insider information.
Stupid Onion Tricks
And now for a few of what Dave Letterman might call "stupid onion tricks," measures that are often claimed to prevent tears while cutting onions. After reading my parenthetical comments, I'll leave it to you to decide how much sense they make.
• Cut the stem end off before the root end. (Any onion with half an IQ will remember the cutting order and behave accordingly.)
• Let a stream of cold water run in the sink while you do the cutting. (When the onion vapors see the water they will rush toward the sink, even if it's halfway across the room.)
• Clamp a wooden match between your teeth. (You'll never notice your eyes stinging, especially if you chew on the match head.)
• Keep a piece of bread in your mouth. (And make sure to chew it ostentatiously, so the onion will know it's there.)
• Wear contact lenses to protect your corneas.
• If you wear contact lenses, remove them because the irritating vapors can get behind them, preventing the tears from washing them out.
• Cut or chop your onions under water. You may either fill the sink with water and do your cutting beneath the surface, or put on your scuba gear and take the job to the swimming pool. (These methods should work, except for the little problem of the onion pieces floating away before you can collect them.)
What Really Works
If you can stand the awkwardness, wear a skin-diving mask. But best of all, just learn how to dice an onion as quickly and efficiently as the chefs do, and there won't be time for the irritating vapors to bother your eyes very much. Several cookbooks, including the new "Joy of Cooking," illustrate the technique.
And remember that using a very sharp knife will break fewer cells and produce less tear gas. It's a good thing. |
