How Onions Make You Cry

By on October 12, 2013
crying when cutting onion

It is a well-known fact that onions make you cry. We have all experienced this while cooking; we start chopping an onion, our eyes start stinging, and the next thing we know we have tears rolling down our cheeks. Blinking or rubbing our eyes only makes it worse.

It has happened to us all, but have you ever wondered why?

When you slice an onion you are breaking apart the cells inside. These release their contents which form sulfenic acids. These acids mix with enzymes to produce a gas called propanethiol S-oxide. As this gas reaches our eyes and mixes with the water in them, it forms sulfuric acid.

This acid makes our eyes sting, which results in more tears and this added water produces more acid, which in turn produces more irritation. Cooking the onion then deactivates the enzyme and our eyes return back to normal. Though there are a number of different suggestions about how we can avoid this, some of them are quite logical and useful but others could be impractical or even dangerous.

How to Stop Teary Onion Cuts

  • Cut the onion under, or near, running water. In theory, this method ensures that the gas gets absorbed by the running water instead of your eyes. It is not very practical from a saving water point of view though, and cutting anything under water is quite likely to end in an injury.
  • Chill your onions first. This is supposed to slow down the amount of acid that is released. The onion does not need to be frozen, just chilled in the freezer for 10-15 minutes and is one of the more sensible options.
  • Wearing goggles. It is possible to actually buy “onion goggles,” although tight-fitting swimming goggles would likely do the same job. They just have to stop any gases from reaching your eyes. It may seem excessive, and you may be ridiculed by your family for standing in your kitchen in swimming goggles, but at least you will know that you can chop as many onions as you like without crying!
  • Some people say that wearing contact lenses helps as the lenses form a barrier for the eye. Others say that wearing contact lenses makes it worse because they make it harder for the eye to produce tears to wash the acid away. Professional chefs tend to just chop them quicker, so that the gas does not have time to reach the eye. This always looks easier than it is, though.
  • Use a very sharp knife when cutting onions. The enzymes are released when cells are broken or crushed. Using a sharp knife slices through the onion rather than crushing and thus, fewer enzymes are released.
  • Cut the onion next to a strong draft from a fan. The fan helps to pull away the gas away from your eyes.
  • Breathe through your mouth (to draw the gas over your wet tongue) or stick your tongue out.
  • Put vinegar on the chopping board. The acid denatures the enzyme.
  • Soak the onion in water. The enzyme is denatured by the water-air boundary.
  • Soak the onion in salt water. The ionic solution denatures the enzyme.
  • The candle method. Light a candle and set it near the cutting board before cutting the onion. The gas released by the onion is drawn into the flame of a candle.
  • Whistle while you work. Whistling makes a significant airflow, specifically away from your face, which keeps the onion mist away from your eyes. Just pick a catchy tune that you won’t want to stop whistling and you can cut as many onions as you need.
  • Chew bread or gum. Many people report that chewing, especially gum, helps avoid tears when cutting onions.

Whichever method you use, it is worth it because onions have lots of health benefits, from lowering cholesterol to being high in vitamin C. So maybe it is worth all the tears after all!

Image courtesy: 7osn.com , etsystatic.com

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