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How to Cut an Onion Like a Pro

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Learn the essential techniques for mastering the art of onion cutting. Say goodbye to teary eyes and hello to perfectly diced and sliced onions as we share expert tips and tricks for effortlessly tackling this kitchen staple. Whether you’re a novice cook or a seasoned cook, you’ll soon know how to cut an onion like a pro.

Overhead shot of different cuts of onion: sliced, diced, and rings.

Using the Proper Equipment

Choosing the right kitchen equipment ensures you can quickly and easily chop your onion while prioritizing the safety of yourself and others in your kitchen. You will need a knife and a cutting board.

Select a sharp knife. While this may feel counterintuitive, a sharp knife is safer than a dull knife. The sharp knife cuts through the onion more easily, so you use less force and are less likely to have the knife swerve or cut through the onion suddenly and injure yourself. Skip the paring knife and opt for an 8 or 10-inch chef’s knife instead. The right size knife helps ensure you have the control you need not to cut yourself accidentally.

For the cutting board, choose something that is large enough to hold at least half of the chopped onion and give yourself room to work. I typically use a large cutting board whenever chopping vegetables. My personal preference is bamboo cutting boards, as they are sustainable and biodegradable, making them an eco-friendly choice.

Pro Tip:

If your cutting board is wiggling around and won’t stay still while you are trying to work, place a thin wet towel between the board and the countertop. It will lock it into place, making your job both easier and safer. A reusable paper towel or wash rag are great options.

Why Onions Make You Cry

Onions make you cry because of a chemical called syn-propanethial-S-oxide. As you cut an onion, you break open the plant cells that release enzymes and sulfenic acid that combine to create the chemical.

This chemical is a gas that is volatile, meaning it easily vaporizes. When it comes into contact with your eyes, it irritates the cells in your eyes, causing them to release tears.

Onions and diced onion on a cutting board next to swim goggles.

How to Cut Onions without Crying

There are a few things you can do to prevent, or at least reduce the tears you cry when cutting onions. Some lucky people aren’t bothered by the chemical compound at all, but if you aren’t one of those lucky people, try these tips.

A barrier between your eyes and the onion vapor is the most effective way to keep you from crying. Regular glasses, a face shield, or even contact lenses can serve as this barrier. Be careful not to rub or touch your eyes when you cut onions, especially if you wear contacts, as the compound gets on your fingers as soon as you make that first cut. The chemical will irritate your eyes even more if it comes into direct contact with them.

“I always find that keeping my contact lenses in stops me from crying, if I don’t have them in then I wear swimming goggles, this isolates my eyes and stops me from crying.”

— Mandy Applegate, Splash of Taste

If you cut the onion under running water, the chemical compound washes away. However, this can make for a slippery surface and is not the safest way to cut a vegetable.

If you don’t wear glasses or contacts, try freezing the onion for a few minutes before cutting. This slows the release of the compounds, but be sure not to leave it in longer than about five minutes. Truly freezing your onion will burst the plant cells and give you a soggy onion.

To keep the air flowing, open the window or turn on a fan or your oven vent. This will prevent that onion vapor from lingering, reducing the chance it will get into your eyes in the first place. Additionally, try drinking a glass of water before chopping the onion. I find that when my eyes are dry, they are much more likely to be irritated by freshly cut onion.

Clean-up Tip:

The best thing to get the smell of onions off your hands is stainless steel. Whether you use your steel faucet, a fancy steel soap bar, or even the blade of your knife, exposing the onion’s chemical compound to steel neutralizes the odor leaving your hands smelling fresh and clean.
Onions sliced into both traditional and half-moon shapes on a cutting board.
Left: a traditionally sliced onion. Right: an onion sliced into half-moons.

How to slice an onion

Different recipes call for different styles of onion pieces. Typically, when slicing an onion, your recipe refers to the traditional slices that are created with the root attached while working perpendicular to the root. However, when a recipe like this crockpot garlic pork specifies half-moon slices, they are referring to crosswise slices, which are created by working parallel from the stem end towards the root. You may also encounter sliced onion rings, which are crosswise slices made from a whole onion that is used for fried onion rings or hamburgers.

When deciding to slice your onion into perpendicular or crosswise slices, consider the flavor impact you want out of your onion. Onion cells are not symmetrical, so the direction you slice will change the flavor. Those crosswise, half-moon shapes will cause the onion to release a stronger flavor, while traditional slices will result in a sweeter, milder flavor.

Start by identifying the root and stem ends of your onion. The stem end will stick out, while the root end may look a little hairy with skinny root pieces still attached. Your first cut is to slice off the stem end, staying close to the top, but removing enough to create a flat surface and expose the layers of the onion. Place the onion cut side down for stability, and slice straight through the root end to cut the onion in half with the root end still holding each half together.

Safety Tip:

Always create a flat edge when cutting vegetables or fruits. The flat end always sits on the cutting board to keep whatever you cut from rolling or sliding. This is a much safer way to cut anything.

Use your fingers to peel back the dried skin from each half of the onion and remove it, then place the long cut ends on your cutting board. For traditional slices, like in this grilled steak with peaches and onion recipe, remove the root end, rotate the onion 90º and slice the onion perpendicular to the root. When you’ve sliced about 3/4 of the onion, rotate it to put the longer flat side on the cutting board to slice the rest. To slice the onion into half moons, keep the root attached and slice the onion starting at the stem end making even crosswise cuts, parallel to the root.

An onion on a cutting board sliced into rings.
An onion sliced into rings.

The process of cutting onion rings is similar to making half-moon-shaped slices. Cut off the stem end, then run the tip of your knife over the top of the onion from root to stem to make a very shallow cut and give yourself access to the skin to peel it back. Remove the skin, but keep the rest of the onion intact. Hold the onion on its side, then carefully use your knife to make even crosswise cuts while working from the stem end to the root end.

You can make your slices as thick or as thin as you need, depending on the recipe. For example, you want thin rings for French onion soup but thicker traditional slices for butternut squash soup.

How to chop or dice an onion

Chopping and dicing can be a bit more intimidating than slicing, but if you can master slicing, you can master chopping and dicing with a little bit of practice. As mentioned above, start the process by removing the stem end, halving, and peeling your onion.

Diced onion on a cutting board.
Diced onion.

Traditional Method

The first method I’m going to cover is called the traditional method. It includes cutting the onion in three different directions, along three different planes. From looking at the onion on a cutting board, we will make one set of horizontal cuts and two sets of vertical cuts, one right to left and one front to back.

Take your peeled half-onion and place the long-cut end on your cutting board. The first cuts are the horizontal cuts. Hold your knife parallel to the cutting board and carefully cut two to three horizontal slices through the onion from the stem end to the root, being sure to leave the root end intact.

Next, the first set of vertical slices will run perpendicularly from the root towards the stem end. Using the tip of your knife and being careful not to cut through the root, slice across the top of the onion to create even vertical cuts. The number of vertical cuts will depend on the size of your onion and the size of pieces you want to obtain. More cuts will result in smaller pieces; fewer cuts will create larger pieces. At the end of this step, your onion should still be loosely held together by the root end.

The second set of vertical cuts is crosswise, starting at the stem end and running parallel to the root of the onion. These are the cuts that will remove slices of onion pieces as you work from the stem to the root. The closer you make these final cuts, the smaller your onion pieces turn out.

Two onion halves with black lines overlaid to show traditional dicing lines versus radial dicing lines.
Left: The lines for vertical and horizontal cuts for traditional dicing. Right: The lines for radial cuts to dice with the radial method.

The Radial Method

The radial method is another approach to slicing an onion, a method that I would argue is both easier to master and gives equally good results as the traditional method if done correctly. When chopping an onion using the radial method, there are no horizontal cuts, which is definitely safer, especially for beginner chefs.

This method calls for two sets of cuts, one set perpendicular to the stem and one parallel to the stem. The first set of cuts, running perpendicular to the stem, are made with the knife at an angle to the center of the onion.

Starting with your halved and peeled onion, place it cut side down on the cutting board. Then using the tip of your knife, slice into the onion from root to stem at an angle towards the center of the onion, leaving the root intact. As in the traditional method, more angled slices will create smaller pieces, while fewer slices will result in a larger chop.

The final set of cuts in the radial method are the same as the final cuts in the traditional method. Start at the stem end and make even slices, working your way towards the root end and removing pieces of onion as you go.

What is the difference between a chopped onion versus a diced onion?

The difference between a chopped and diced onion is purely the size of the pieces you have at the end. Chopped onions are larger chunks, while diced onions are smaller pieces.

Chopped onions are common in recipes where the onion gets cooked with other large ingredients, like soups and stews where the onion needs to hold together with other ingredients. You want a smaller dice for recipes like shepherd’s pie or homemade baked beans.

When a recipe asks for chopped onion, the pieces are about a half inch in size, so adjust your cuts to be about a half inch or slightly further apart on the onion. Diced onions are smaller and typically closer to one-quarter inch in size. To dice an onion, make your cuts closer together.

Overhead shot of different cuts of onion: sliced, diced, and rings.

You’re ready to cut onions like a pro

The next time you have a recipe that calls for an onion, no matter what shape or size you need to cut it, you have the tools you need to do it well and to do it quickly. Follow the steps, and with a bit of practice, you will be able to have your onion sliced, chopped, or diced in under a minute.

Portions of this article first appeared on Food Drink Life.

About Renee N Gardner

I'm the recipe developer, food photographer, and mastermind behind Renee Nicole's Kitchen, where I help create kitchen confidence to inspire home cooks to become home chefs. No fancy fads here, just high-quality, homemade recipes featuring seasonal ingredients.

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