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Onions 101: Expert advice on How to Prevent Tears When Chopping Onions

An onion’s ability to make you cry is its self-defence mechanism. But here’s how you can combat tearing up

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By Epicurious US | October 13, 2023 | Recipes

It doesn’t take a lot to move me to tears—a sad song, Episode Three of The Last of Us, and sometimes, just slicing through an onion. And while wistful situations are easy to avoid in daily life, I cut onions and their other allium cousins (looking at you, shallots and leeks) several times a week, whether I’m slicing for fajitas, chopping with carrots and celery as mirepoix for soups, or peeling, quartering, and blending into a marinade. I cry almost every time.

When I worked in a diner, I used to take breaks from chopping onions to stand in the walk-in freezer for a few seconds when the tears became too much—it always seemed to help. My co-workers at the time offered any number of borderline-superstitious solutions, including chewing gum while chopping and holding a match between your teeth as you slice and dice. I recently polled my colleagues at Epicurious and Bon Appétit to see what the scuttlebutt was on preventing onion eyes. The match trick came up quite a few times, always with the caveat that it didn’t seem to work. Some also suggested sticking out your tongue while cutting, wearing onion goggles, lighting candles, refrigerating or freezing the onions beforehand, and, of course, having someone else cut them for you.

I spoke with Dr. Stuart Farrimond, food science presenter for the BBC, who shed some insight on the issue. “Understanding a little of why onion slicing is such an eye-stinging ordeal helps you dice onions without turning you into a snotty, blubbering mess,” he says. Essentially, the onion uses its ability to make you cry as a self-defense mechanism—damaging the cell walls of an onion causes a specific chain of events. Cutting the onion releases a chemical, which then combines with an enzyme, producing a new chemical, which combines with yet another enzyme to create a final molecule, a sulfine called syn-Propanethial S-oxide. “This rapidly wafts out from the oniony juice and when it reaches the surface of your eyes, it reacts with the thin layer of water covering your eyeball to create sulphuric acid, among other harmful and irritating substances,” Farrimond explains.

The first step to preventing tears-by-onion is making sure your knives are sharp. Image via Pexels.

Now that we know what’s going on inside the onion when we cut into it, a few options for tear prevention become clear. Start by making sure your knives are sharp. “A well-honed knife will divide the flesh, damaging and bruising the least number of cells possible,” Farrimond tells me. Next, we can try slowing down the chemical reaction. “Chilling onions by storing them in the fridge or giving them a 30-minute blast in the freezer slows down the enzymatic chemical reactions, dramatically delaying the onion’s defensive gas-producing processes,” Farrimond says.

A simple way to keep onion’s self-defence mechanism is cutting onions near a strong fan that’s blowing away from you. Image via Pexels.

If you’re particularly sensitive to onions’ self-defense mechanisms, you can try to intercept the onion mist on its way to your eyes. This is the theory behind methods like lighting candles or matches near your kitchen workspace—the flame ostensibly works to neutralize the onion’s gas on its way through the air. While I didn’t have any success with the flame method, Farrimond has a few more suggestions.

Farrimond recommends cutting onions near a strong fan that’s blowing away from you. He also suggests cutting the onions under running water, but says that submerging and cutting the onions in a large bowl of water is even more effective (the danger involved in this method outweighs the advantage, in my opinion). And finally, as long as you’re okay giving up your future as a fashion icon, there is the dorky, but effective option of onion goggles.

Cutting onions under water in a large, deep tray is effective, but inefficient unless you’re just quartering or doing a rough chop, says experts. Image via Pexels.

I tested all of these suggestions, as well as some of the more, ahem, interesting methods my colleagues offered, and found that chilling the onions really did help quite a bit, but wasn’t always 100% effective. I’ll toot my own horn and declare here and now that my knives are always well-sharpened and honed, so I know this wasn’t a factor for me. Cutting onions under water in a large, deep tray is effective, but inefficient unless you’re just quartering or doing a rough chop where precision doesn’t matter—it was also trickier to see where you were cutting, which felt like a safety issue. And it pains me to say this, but yes, the onion goggles were effective, especially with Farrimond’s added note to use nose plugs to prevent the lachrymatory factor (those nasty chemicals that trigger a tear response) from traveling through your nose and to your eyes.

While some of my colleagues’ advice lined up with Farrimond’s (bravo, friends), many of the most common suggestions were ineffective, leaving me crying in my kitchen yet again. I think Farrimond sums it up best: “Putting a spoon in your mouth, a ball of bread under your top lip, or poking a match up your nose do nothing more than make you look a bit daft.”

The story originally appeared on epicurious US.