Tired of Crying Over Onions? Physics Has the Answer
Tears over onions have been haunting cooks for centuries. People have tried everything to fight them off—refrigerating the bulbs, wearing goggles, even chewing bread while slicing. Some go as far as putting in contact lenses before they start chopping. The kitchen has turned into a testing ground for hacks, but the problem still persists.
Image via iStockphoto/yamasan
It’s become such a stubborn mystery that researchers decided to put onions under the microscope and run experiments to find out what’s really going on.
The Sting in Every Slice
Onions are fully prepared to defend themselves with their own brand of chemical weapons. When you slice into one, its enzymes break apart cell walls and create a chain reaction that produces a volatile irritant called syn-propanethial-S-oxide.
The gas rises and stings the nerves in your eyes while sending your tear ducts into overdrive. It’s a neat survival trick for the plant, but frustrating for anyone just trying to get dinner on the table.
For years, the explanation stopped there and left cooks to invent their own strategies. But now we realize we’ve been asking the wrong questions about which chemical causes the tears instead of how our cutting habits play a part in making it happen. That’s what Cornell physicists decided to tackle.
Science Meets the Cutting Board
Image via iStockphoto/Aleksei Isachenko
The team set up a custom slicing device and coated onions in black spray paint so they could track every droplet released. With high-speed cameras rolling, they tested blades ranging in thickness from razor-sharp to noticeably dull, and varied cutting speeds between slow and forceful.
The results explain a lot about why some nights in the kitchen leave you crying harder than others. Thin, sharp blades sliced cleanly and produced fewer droplets that moved with less force. Dull blades bent the onion flesh before cutting through and built up pressure until it burst. That burst sent juice flying and created up to 40 times more particles than a sharp knife.
Faster chopping didn’t help either. It produced as many as four times more irritants compared to slower slicing. Some droplets even reached speeds of around 141 feet per second.
To top it off, the study busted the popular myth that refrigerating onions calms the burn. The researchers tested that, too, and found the opposite. Chilled onions actually released a noticeably larger volume of droplets compared to room-temperature ones.
While the study was focused on onion irritants, the findings also raised another point. The droplets released when slicing raw produce can carry surface-borne pathogens. Sharper blades also reduce the spread of those airborne particles.
For home cooks and food professionals alike, that’s a reminder that a well-honed knife is non-negotiable in the kitchen.