For millennia, chopping onions has been synonymous with tears. The culprit? A volatile chemical compound called propanethial S-oxide, released when onion cells are damaged. However, new research from Cornell University offers a surprisingly simple solution: using sharper knives and cutting more slowly.
Understanding the Science Behind Onion Tears
The research, led by biomechanist Zixuan Wu and physicist Sunghwan Jung, delved into the mechanics of onion mist creation. They used a mini guillotine, high-resolution cameras, and sensors to precisely track droplets expelled during cutting. Their analysis revealed that the speed at which this mist is released is significantly faster than the speed of the blade itself.
How Knife Sharpness and Speed Matter
The study pinpointed two key factors influencing mist creation: the sharpness of the blade and the speed of the cut.
- Dull Blades and Rapid Cuts: Blunter knives require more force to break through the onion’s layers, causing pressure to build within the onion’s juices. Forceful, quick cuts with a dull blade propel droplets even further – sometimes at speeds up to 40 meters per second (144 kilometers or 89 miles per hour).
- Sharp Blades and Slow Cuts: Conversely, sharp blades make clean slices, minimizing cell damage and the release of irritating compounds. Slower, gentler cuts further reduce mist production, keeping droplets below eye level.
Debunking the Chilling Myth
A common kitchen practice is to chill onions before chopping, believing it reduces tear production. However, the Cornell team’s research debunked this belief. They found that the initial temperature of the onion had little to no impact on mist release, and in some cases, chilling could even exacerbate the problem.
Implications Beyond the Kitchen
The research isn’t just about avoiding tears. It has broader implications for food safety. The way onions are cut can influence how easily pathogens spread. If bacteria are present on the onion’s surface, cutting style determines how far those bacteria are dispersed via droplets. As exemplified by recent outbreaks of E. coli linked to onions, proper cutting techniques can significantly limit the risk of widespread contamination.
“Suppose you have pathogens on the very top layer on the onion,” says Jung. “By cutting this onion these pathogens can become encapsulated in droplets where they can then spread.”
This research builds on a long history of culinary practices—onions have been a kitchen staple for roughly 5,000 years—and even inspired literature, as evidenced by Shakespeare’s observation of onion-induced tears in Antony and Cleopatra. Thanks to this new understanding of onion mist mechanics, we can now chop more safely and comfortably.
