How to avoid crying too much when cutting onions (according to scientists)

The Star

22-05-2025

It's better to have a sharp knife blade to avoid crying (too much) when cutting an onion. — Photo: andreygonchar/ Getty Images, via ETX Daily Up
When you cut an onion, a gas is released that comes into contact with the tear fluid in your eyes. In short, it makes you cry, and it's almost unavoidable. But researchers have discovered that there's a simple way to minimise this inconvenience.
Crying when chopping onions is the most natural reaction there is, but that doesn't stop it from being annoying. And who hasn't tried the many tips and tricks that are touted as ways to prevent tears when slicing these kitchen staples?
There's the match or the slice of bread in the mouth. Or how about running your wrists under cold water before setting to work, or putting an onion in the freeser for 15 minutes before cutting it?
Otherwise, you could simply put on a diving mask, as suggested in a number of humourous videos on social networks. Or you could try running the knife blade under a trickle of lemon juice...
But the knife may be the key to the solution, according to a recent experiment conducted by researchers at Cornell University in Ithaca, New York, and reported by New Scientist.
The question is... how sharp is your knife? In other words, is it blunt? Because in this case, there's a very good chance that cutting an onion will make you cry.
Indeed, the conclusion of the study, conducted by researcher Sunghwan Jung and his team, is that a knife that doesn't slice well can generate up to 40 times more droplets than a well-sharpened blade. This is because the onion's skin bends, increasing the pressure inside.
The scientists' experiment involved cutting brown onions with different blade thicknesses and at different speeds, and analysing the effects.
The process was filmed using a high-speed camera. And to better visualise how the onions reacted to the maneuver, they were spray-painted black. The scientists found that there were fewer droplets when the blade was sharp. Also, slicing very quickly multiplied the quantity of these particles fourfold, compared to slow slicing.
Indeed, peeling an onion triggers the release of a gas. When this gas comes into contact with the tear fluid in our eyes, it turns into sulfuric acid. Initially, onions absorb sulfur from the soil, which is stored in the cells of the vegetable. When sliced, the molecules are released, which in turn meet ensymes, and are eventually turned into a volatile, irritant gas. The result is as immediate as it is unpleasant: we cry! And that can be annoying when you have several onions to chop, and you need to see what you're doing.
And if your knives aren't sharp enough, did you know that scientists have (also) developed onions that don't make you cry? These are marketed by the Sunions brand. They are the result of over 30 years' research in the US states of Nevada and Washington. — AFP Relaxnews