Onions are one of the most commonly used members of the allium family. They gain their distinct and pungent flavor from their use of sulfur, which growing onions take from the soil and store in their cell fluids. It is one of these sulfur byproducts that causes your eyes to water when you chop an onion, but chilling an onion can reduce that effect.
How Onions Make You Cry
When you cut into an onion, you release sulfur and enzymes from the onion's cell walls into the air. One of these sulfur products is a lacrimator, and as it reaches your eyes and nose, it contacts your nerve endings directly. This hit of sulfur byproduct then breaks down into hydrogen sulfide, sulfur dioxide and sulfuric acid. The effect of these molecules on your nerves is very powerful and it triggers a tearing reaction in your eyes.
How Chilling Affects the Onion
When you chill an onion, either in the refrigerator or in a bowl of cold water, the enzymes in the onion slow down at a molecular level. This means that when you cut into a cold onion, the slow-moving enzymes and sulfur molecules have less momentum when they combine to make the irritating sulfurous molecules. They also move much more slowly as they escape the onion walls and often will not reach your eyes or nose. This simple tactic can greatly reduce or eliminate an onion's ability to make you cry.
Side Benefit of Chilling an Onion
If you chill a whole, unpeeled onion in a bowl of ice water for half an hour to an hour, the ice water will hydrate the onion's skin. This hydrated onion skin is not as brittle as dry onion skin and also stronger, which means it is easier to peel. Hydrated onion skin can be easily peeled off in large pieces, while dry, brittle onion skin often flakes off in many small pieces or sticks to the inner layers of the onion.
Other Methods To Reduce Tears
Cutting onions near a candle or other open flame may minimize the amount of sulfuric chemicals that reach and agitate your eyes. America's Test Kitchen recommends specialty onion goggles, designed to block your eyes. Regular swim goggles will work, as well, but may not be as comfortable. Keeping the cut side of the onion away from you will also help reduce your exposure, and running your range ventilator may remove some of the chemicals from the air.
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