Why Chopping an Onion Makes You Cry

Our family loves onions. All three kids love them. Steve loves them. I love them. I add them to any dish I can where it won't be completely odd to sneak an amaryllis lovely into; and I adore the aroma of chopped onions and garlic simmering in my kitchen. So last night while I was chopping two plump red onions to add to my sizzling pan, I wondered how something so terrific could make me CRY!

Photo by Darwin BellIt seems that when you slice into an onion, you break open onion cells that have enzymes inside of them. When these enzymes are cut open, they escape and then decompose some of the other substances (amino acid sulfoxides and sulfenic acids) that have been released from the sliced cells. These substances rapidly rearrange themselves into a volatile gas.

This gas then reaches your eyes and reacts with the natural water that keeps your eyes wet and it changes the form of the chemical again, generating a sulfuric acid that irritates your eyes. The nerve endings in your eyes are extremely sensitive and they relay the message to your brain that something is suspicious and that you need to start making more tears, to protect your eyes by diluting that annoying acid.

That volatile compound that stirs up the crying problem in the first place is ALSO responsible for making the onion taste so yummy and giving off such a delectable smell.

Green onions, leeks, garlic, and shallots do not make us cry because while they produce sulfenic acid when cut, they have fewer LF-synthase enzymes and don’t produce syn-propanethial-S-oxide.

A few tips to aid in the prevention of onion weeping include:

1. Chill or slightly freeze the onion before cutting, as it will mildly change the chemical reactions and reduce the gas released.

2. Cut fast! (my method)

3. Cut the onion under running water, as it prevents the gas from reaching your eyes as quickly.

4. For the extremely sensitive, wear goggles. I know that nobody wants to wear scuba gear to prepare dinner; but hey, extreme onion situations sometimes call for extreme measures.

Photo by Darwin Bell