James Kenji Lopez-Alt
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The Mathematically Best Way to Cut an Onion
🕑 Added 2025-01-21 19:41:24 +0000 UTCDicing an onion is perhaps the culinary task performed more than any other. It's the first step to countless recipes and something that every cook in every restaurant in the world has done hundreds or thousands of times.
But have you ever wondered if there's a truly best way to dice an onion? I did! So I went on a quest for the perfect onion-dicing technique; the method that produces the most even dice with the fewest number of knife strokes.
Here's what I found:
The classic method isn't best: While the standard vertical and horizontal cuts work just fine, they lead to uneven dice, especially around the edges of the onion.
Radial cuts aren't the answer: Angling your knife towards the center might seem intuitive, but it actually results in even less even dice.
The sweet spot is somewhere in between: For the most even dice, angle your knife towards a point about six-tenths of the onion's height below the cutting board.
Don't sweat it too much: At the end of the day, most onion-cutting methods will work just fine. This is really just for the nerds.
To figure this out, I started by revisiting the classic method I learned way back when I first started cooking. You know, the one from Jacques Pepin's "La Technique" – trim the top, split it in half, peel it , and then make a series of pole-to-pole vertical and horizontal cuts, keeping the root end intact to keep the layers together until you cut against those slices to release a shower of dice. It's the technique used in most culinary schools and restaurants, and it's what I'd always done in the past.
The other common method, touted by folks like Alton Brown is the "radial" or "Lyonnaise" cut, where you angle the knife towards the center of the onion.
To test the relative efficacy of these two methods, I enlisted the help of Rui Viana, a friend of mine from college who built a computer model that simulates the cross section of an onion, allowing you to overlay various slicing patterns on top of it and calculating the total number of pieces that are cut, as well as the standard deviation in piece size. (An even more robust model can be found here).
Using this model, it turns out that the radial technique actually produces dice that are even less even than the standard technique (this is because the with radial cuts, you wind up with fat arcs near the outer layers of the onion, but tiny wedges towards the center.
What we we found was that angling the knife towards an imaginary point below the cutting board about six-tenths of the onion's height below the surface resulted in the most even dice with the fewest number of strokes. About 30% more even than the standard method.
Now, does this mean your onions will taste 30% better if you use this technique? Probably not. I cooked various dishes with onions cut different ways and the differences were pretty subtle if detectable at all.
At the end of the day, there are tons of ways to cut an onion, and most will work just fine.
What about the tears?
As for the other big onion quesiton–how to stop yourself from crying when cutting onions–unfortunately, there are only two methods that work with reliable effectiveness.
We cry when slicing onions because of the lachrymators–irritating sulfurous compounds–that are produced when onions are sliced open. The only way to stop the tears is to stop those chemicals from reaching our eyes. Using a sharp knife to limit the crushing of cells helps, as does working in a well-ventilated area (try slicing onions under the hood of your stove or with a fan blowing over the onions, away from you and towards an unwitting victim, perhaps). Chilling the onions to slow the chemical reactions that create these lachrymators also helps to a small degree.
But by far the best method is to just block your eyes. If you wear contact lenses, you've probably already noticed that onions don't affect your eyes very much. Swim goggles will also do the trick (not ski goggles, which are vented).
Also, it helps if you don't anthropomorphize your vegetables.
Comments
Dina from across the pond
I notice some carbon steel knives in the background. I love carbon steel over stainless steel. Can you do a show on knife selection, care, sharpening and how often you do sharpen? Thx so much.
rekoJ (Pronounced Wreckage)
What a moronic request. Please stop
Ro
Please stop these comments.
L.N.
Please stop painting your nails thanks so I can resubscribe
Jessica Han
Kenji! I love watching your teriyaki reviews and I wanted to recommend my mom’s restaurant in Totem Lake. It’s called Teriyaki Plus Kirkland!
Dylan Poulsen
Thanks for the link to my blog post. For anyone interested in an even deeper dive on the more robust mathematical model, I have more details in slides for a talk I gave:https://drspoulsen.github.io/MARP/
Jon
Also I’m pretty sure the tear-inducing parts are concentrated mostly if not entirely in the root? I cut the top and bottom and when slicing leave a half centimetre or so at the bottom to keep the thing together. Then you can either chop that bit or just discard it because it’s usually tough and bulb-y anyway. I never had a problem with tears.
Ann Miller
Thanks for this. Something this helpful will have me joining your paid group!
Adam Schumacher
Re: tears, cutting under the range hood has worked well for me. Even on low speed, that little bit of updraft pulls most of the irritants away from my face and out the vent. I figured this one out when I switched to an induction cooktop and started using the range as additional prep space.
EnthusiasticOwl
sharp knives
James Carey
Love these sorts of posts. BTW you look so healthy👍
Barbara Llewellyn
Why aren’t you crying by now?
Rob L
If you were a home cook, any reason not to remove the root end at the same time I'm removing the stem end? Makes getting the outer layer off easier and avoids putting my knife down?
