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How to Chop an Onion

  • We can say with the utmost confidence that there are few (outdoor) kitchen skills more essential than chopping an onion. We know because, well, we work with a chef every day! (That’s Chef Tony, for those of you just visiting us for the first time.) Onions are also one of the most popular ingredients on the globe, so it’s nearly impossible to avoid chopping these treasured veggies if you take things seriously in the kitchen and like to try new recipes. In fact, we’ve seen foodies so moved by this universal kitchen task that they were brought to tears! What’s that? Chopped onions actually make people cry because their broken skin releases enzymes and sulfenic acid, which then merge to create propanethial S-oxide, an irritating gas that triggers tears as our eyeballs rush to flush it out? Sounds like a bunch of complicated, sciency gobbledygook — but let’s just go with it for now.

  • Person chopping an onion on a cutting board

No matter your feelings about the humble onion, learning how to chop one will save you valuable prep time whenever dinner beckons one of these beautiful bulbs. We asked the aforementioned Chef Tony to walk you through the whole process, and he went the extra mile by demonstrating 2 methods for achieving the chop of your dreams. We hope you’re not weeping for joy, because practicing this essential food-prep skill is a real tear-jerker. Remember to always chop slowly and carefully (at least at first), saving the speed runs for when you’re more comfortable with the technique. Now let’s get chopping!

What You'll Need:

Step 1: Trim the Stem

Before diving into this tried-and-true technique, make sure you’ve sharpened your kitchen knives. A sharp blade is always safer to use, and cleaner cuts will keep the onion’s irritating fumes to a minimum. When you’re ready to start, turn the onion on its side and observe the 2 ends: the stem and the root. The root end will look exactly like it sounds, with stringy roots shooting out from a tight center. That leaves the stem on the other end, which usually raises to a small point covered with flaky skin. Secure the onion to the cutting board with your off hand and trim about ½” from the stem, exposing a bit of the onion’s flesh below. Discard the trimmed piece.

Step 2: Halve & Peel

Stand the onion upright, using the flat, newly trimmed area as a base so the root end faces up. Again securing the onion with your non-knife hand, cut it in half with a downward slice, leaving the roots intact. Peel and discard the skin, then turn both onion halves down on their flat ends — this is how you’ll work with each half in the following steps, plus it’ll keep those tear-provoking gases trapped on the cutting board for longer.

Step 3: Cut Horizontally

For the remaining steps, work with a single onion half at a time and keep the flat sides down; this provides much more stability for your knifework. Turn the onion so one of the sides is facing you, then make 2 horizontal incisions from the stem end, one about a third of the way up the onion and another about a third of the way down. Be overly careful on these cuts, applying slight downward pressure on the top of the onion with your off hand to give the knife some resistance. The last thing we want is a slipped knife and a trip to the emergency room, which is again why it’s so important to have a sharpened blade for any kitchen cutting.

Whole and chopped onions on a chopping board

Step 4: Slice Vertically

Rotate the onion so the trimmed stem end is facing you or angled slightly toward your knife hand. For this next series of slices, make sure you’re using the “claw” technique with your off hand. Bend your fingertips about 45 degrees, placing the middle 3 fingers on top of the onion with the thumb and pinkie behind the vegetable’s curve. Use your top 3 fingers to press the onion into the cutting board and guide your knife, while the back 2 fingers slightly push the onion toward your blade. This not only allows the knife to do all the work over the stabilized onion, but also protects your fingertips from its (hopefully) sharpened edge.

With the claw safely and securely gripping your onion half, slice lengthwise from stem to root, but don’t cut completely through the onion. Aim to slice about ¾ of the way to the root so that end remains intact and the slices hold together. Now’s the time to decide how large you want your chopped onions to be; smaller bits (minced or fine-chopped) require more lengthwise cuts, while larger chunks (rough-chopped) call for fewer slices. Your eyes may be watering at this point, so feel free to raise a fist to the sky and curse chemistry before proceeding to the next step.

Step 5: Chop Crosswise

This final step is where the onion-chopping technique differs, and Chef Tony was gracious enough to showcase both options for us. Each method makes use of crosswise cuts from side to side instead of stem end to root end, turning those slices from the previous step into small cubes for a variety of cooking techniques. Rotate the onion halves so the slices are horizontal, get that claw grip back in place, and check out your options:

  1. Use the flats of your 45-degree knuckles as a guide for the top (note: not the edge!) of the knife. Working from one end of the onion to the other, move the knife up and down in a chopping motion as your claw pushes the onion toward the blade. Start slowly, and with practice over time, you’ll gradually increase your speed for rapid chopping that’ll save time in the kitchen.
  2. Again using your bent fingertips as a guide for the knife, make rocking, orbital cuts with the point of your knife remaining on the cutting board. Push the onion along as you chop, beginning carefully and working on knife speed once you’re comfortable with the movement.

When finished with your chop of choice, feel free to continue cutting the onion cubes if they’re larger than you intended. Remember to practice these techniques slowly and carefully; speed will come over time as the technique becomes more natural. Once chopped, you can toss those onions in the pan, refrigerate for a few days, or freeze. Just don’t let them linger in the fridge for too long — their flavor becomes more pungent over time, and they should be discarded if you find them particularly slimy or smelly. While you’re here, why not learn more about slicing vegetables?

How to Avoid Crying While Chopping Onions

Remember that old bit from up top about how onions release tear-inducing propanethial S-oxide gases when their skin is broken? We did some more research, and as it turns out, it’s all true! Science also has answers for sidestepping the sobs, including but not limited to:

  • Using a sharp knife; cleaner cuts expel less fumes
  • Keeping the flat side of the onion halves down to trap those gases on the cutting board
  • Working quickly, then washing or wiping down the cutting board and knife for minimum exposure to the fumes
  • Wearing goggles (stylish and tear-free!)
  • Cutting near your kitchen vent or a fan

Of course, the gases will linger on your hands unless you wear gloves when doing kitchen work. It’s always a good idea to wash your hands after working with food, but if you find the onion’s odor and pungent fumes are stubbornly sticking around, rubbing your hands on stainless steel will remove the smell through more sciency magic. With the technique in the bag and a strong line of defense against those pesky propanethial S-oxide fumes, you’ll be an unstoppable chopping champion in no time!