Having been an avid cook for several years, I’ve lived through the pleasant experience of rivers of tears involuntarily gushing out of my eye sockets on the occasions I peel and cut my own onions or shallots many times. But what’s the phenomenon that so brings us to tears? It seems that it’s just our body reacting to some fun chemistry. Here’s a more detailed explanation.Onions are of the genus Allium
, which also encompasses plants such as garlic and chives. On cutting these vegetables open, two substances are liberated: sulfoxides, which are volatile organic molecules responsible for the flavors of the onion; and the allinases, which are enzymes, as the suffix suggests.
These enzymes, like the tricky rascals they are, transform the sulfoxydes into a third scoundrel on contact with air -highly unstable sulfenic acid. In turn, this summarily converts to a fourth substance called (take a deep breath) propanethial-S-oxyde. This is actually a delightful mélange of sulfur dioxide, hydrogen sulfide, and sulfuric acid, and it propagates through the air around your dutiful culinary head and evokes the familiar tear reflex. This reaction is simply an involuntary defense mechanism which attempts to dilute and flush out the malevolant cocktail now aggregating on your eyeball.
There are a few techniques you can employ to minimise this odious occurence. Chopping an onion underwater deprives it of the oxygen needed to complete its devious eye-hating conversions; chilling or cooking the onion makes the process more agreeable as well. You can also turn on a fan to physically blow away the contemptible fumes. Or, if you’re intense enough, you could perhaps keep a pair of anti-onion fume goggles in the kitchen to form an air-tight and virtually impermeable optical sanctuary.