If you want to stop crying while slicing onions, use a sharper knife.
That’s the conclusion by Cornell University scientists who found in a new study that sharper blades cause onions to release fewer tear-producing particles when they’re cut.
The researchers used digital imaging and tracked the particles released from onions, according to their abstract published on the ArXiv server of preprint papers.
The particles contain the chemical syn-propanethial S-oxide, which causes people to tear up, according to the American Chemical Society.
The scientists found that the droplets first come out of the onion at high speed due to pressure on the vegetable’s first layer, followed by the fragmentation of other material released from the onion.
The scientists then tested blades of varying sharpness being used at varying speeds. Cutting fast and cutting with blunter blades increased the amount of droplets and the energy with which the onion expelled them upon contact.
Since the onion’s outer layer is tough, blunter blades and cutting at speed compress the inner layers, thereby creating more pressure that expels more of the tear-causing droplets. Blunter blades caused as much as 40 times more droplets while cutting fast caused four times as many compared to when an onion was cut slowly, the researchers said in their paper.
Sharper blades produced fewer droplets from cutting and the droplets that were produced were expelled at lower speeds, the researchers said. Cutting slower also helped reduce the amount of droplets.
“Our findings demonstrate that blunter blades increase both the speed and number of ejected droplets, providing experimental validation for the widely held belief that sharpening knives reduces onion-induced tearing. Beyond comfort, this practice also plays a critical role in minimizing the spread of airborne pathogens in kitchens,” the researchers said.
