How to chop an onion

Lynn Wright / 15 January 2016

Chopping an onion safely is a key kitchen skill for any cook. Master the art of chopping an onion with our step-by-step guide.



From soups and sauces to stews and casseroles, many recipes call for chopped onions as a way to add flavour, so it makes sense to know how to safely chop an onion without worrying about slicing your fingers.

Take the frustration out of preparing onions with our easy-to-follow instructions for chopping onions safely.

Find out how to sharpen a kitchen knife.

How to chop an onion

1. Place your onion on a chopping board and hold it firmly with one hand. Using a sharp knife, cut off the top of the onion and then cut it in half through the root end.

2. Peel the skin on both halves. Remove any brown or discoloured layers from the onion too. Place the onion halves cut-side down on the board to keep them stable during cutting.

3. With your knife parallel to the chopping board, make three or four horizontal cuts through one of the onion halves – but be careful not to cut through the root.

4. Now make vertical cuts lengthwise down through the onion – again up to, but not through, the root.

5. Finally, turn the onion so that the wide end faces the knife. Hold it firmly with your fingers curled slightly under so your knuckles press against the side of the knife as you cut. This will help protect fingertips from being cut. Slice downwards across the width of the onion to finely chop it into small pieces, moving your fingers back as you chop. Continue until you get to the root, which can be discarded.

6. Repeat the process on the second onion half.

Tips for chopping onions without crying

Many people dread chopping onions because it leaves them with stinging eyes that stream tears. The reason for this is that enzymes in the onions release a gas when it is cut. When this hits the water in your eyes it forms sulfuric acid, stimulating the eye to release tears to wash the irritant away.

There’s no hard and fast solution to this problem but anything you can do to stop the fumes from reaching your eyes will help limit the tears. Here are a few simple tips.

  • Wear eye protection. Contact lens wearers can chop with impunity because their lenses create a barrier between eye and the onion gases. Try a simple pair of glasses, swimming googles or special onion googles to stop the fumes from reaching your eyes.
  • Turn the cut side of the onion away from your face when chopping.
  • The enzymes in cold onions react more slowly when cut, so chill your onions in the freezer for 10 to 15 minutes or 30 minutes in a fridge before cutting them.
  • Use a fan or a strong draft from an open window to blow the fumes away from your face as you slice the onion.
  • Chop onions in a food processor to contain the fumes – but remember to shield your eyes when you open the lid.
  • Use fresh lemon juice to help dissipate the onion fumes – wipe your knife with the juice before cutting an onion.
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