The Refrigerator Hack That Makes Cutting Onions Tear-Free
There's nothing quite like the aroma of onions simmering in a sauté pan. Millions of recipes start with a pile of chopped, sliced, or diced onions, like French onion soup and even basic homemade chicken stock. The veggie is an integral part of the "holy trinity" in Creole cooking and makes up one-third of a French mirepoix. The trouble is, you have to cut your onions before you use them, and that can bring almost anyone to tears. However, it turns out that there's no need to punish your eyes when you're making something with onions. All you need to do is pop your onions in the refrigerator for a few minutes before it's time to cook and you will significantly reduce the aromatics that make your eyes water.
Chefs and cooks have a lot of superstitious ideas about how to save your eyes when chopping onions, like holding a piece of bread in your mouth while you work or covering your knife blade in lemon juice, for example — and most of which don't work (including those two methods). Chilling your onion, however, is one of the few tricks that actually gets results. So if you've got a stack of onions to slice you don't need to don a pair of goggles; simply cool those alliums down before they hit the cutting board.
Why do onions make you cry?
Onions are root vegetables packed with vitamins and minerals. While onions are growing in the soil, they absorb a ton of sulfur to make amino acids like cystine and tryptophan. When it comes time to make some caramelized onions and you start slicing, the knife breaks open the vegetable's cells and releases liquid full of those sulfury amino acids. These acids mix with other compounds to make syn-propanethial-S-oxide, which is a volatile chemical, according to Brittanica. No, volatile doesn't mean it's bad; in this case volatile means that the chemical is easily evaporated into the air. Once it's airborne, it can easily reach your eyes where it irritates the delicate tissue, and your tear ducts produce moisture to try and flush it out. The more you chop your onions, the more syn-propanethial-S-oxide is released, and the more intense things get for your eyes.
So if you want to stop the tears, you have to control the syn-propanethial-S-oxide from getting made in the first place. By cooling your onion down in the refrigerator or freezer for 10 to 15 minutes, you will slow down the release of the enzymes in the onion juice, and therefore slow down the creation of syn-propanethial-S-oxide. While you can't prevent all of the tear-jerking onion juice from getting released, chilling will certainly limit your exposure.
Other tips that work
If you're very sensitive to onions, chilling them before cutting them will help a lot, but there are a few other tricks you can employ to keep your eyes from suffering. The most important tactic is to make sure that your knife is very sharp. A dull knife will squeeze the vegetable while you're cutting, which will damage more of the cell walls and release more enzymes. A sharp knife, on the other hand, will do less cell wall damage. Try to also always keep the cut side of the onion face-down on the cutting board to keep the syn-propanethial-S-oxide from becoming airborne.
It's also a good idea to cut your onions near a hood fan or turn on a ceiling fan to get the air moving. The fan will blow air around and dissipate the chemical compound, so it won't be as concentrated when it hits your eyes.
Now that you know where the tears come from when you're cooking with onions, be sure to use these techniques to keep your eyes dry. On the plus side, if you have some cut onions left over, put them in a container with cut avocados; the same vapors that make you cry will also keep your guacamole green.