Don't cry over your onions!

     After I posted a picture of myself cutting 50 lb of onions on Facebook a couple weeks ago, I got many people asking me the same question: did you have to wear goggles to prevent the tears from pouring down. The answer is, if you cut the onions the right way, you don't get teary. Allium species including onions, garlic, chives, and leeks are able to synthesize a unique set of secondary sulfur metabolites derived from the amino acid cysteine. When the tissue in the onions are crushed during chopping, an enzyme called alliinase is activated to break down the amino acid-based compound S-alkyl-L-cysteine S-oxide (alliin) to an alkylated sulfenic acid and 2-aminoacrylate. When two sulfenic acid molecules condense, they produce a  new compound called allicin. Sulfenic acid will bind to another enzyme, lachrymatory factor synthase (LFS), producing a volatile compound, propanthial S-oxide, a.k.a., the tear-inducing factor that makes you cry like a baby. 

                    

     I have heard of some absurd ways to reduce the unpleasant eye irritation caused by onions. Like, cutting onions in water, or chill the onions before cutting (to slow down the activities of the enzymes in onion), or just wear a pair of ski goggles. I have tried some of the methods above. Some worked, some didn't. And then one day in my cooking class, I finally learned the most legit and reliable way of cutting onions without getting teary. The key is, to cut along the grains of the onion, so that you crush the min. amount of cells which in turn will release the min. amount of lachrymatory factors. Since then, I have passed the trick to many people around me who suffered the eye irritations by onions. But judged from the confused looks on my friends' faces after they got my verbal description, I decided to make a quick sketch to illustrate what I mean by cutting onions "the right way". This by no means the only way to cut onions. But at least to me, I now seldom shed a tear while cutting these troublemakers.

After Step 4 in the illustration, you will get diced onions. If you want to get really small dices, you need a Step 5 to slice the onion horizontally. Imagine the cuts in Step 3 are on the x axis, cuts in Step 4 are on the y axis, then Step 5 would be on the z axis, perpendicular to Step 3 and 4.  If you want to julienne the onions to get slices, stop at Step 3. If you want onion rings on your burgers or something else, you need to halve the onion along its waist to get a cross section in Step 1.