Cornell University researchers have solved a kitchen mystery by demonstrating that sharp knives produce fewer and slower-moving droplets when cutting onions compared to dull blades. The findings used high-speed cameras and particle tracking to analyze droplet formation during onion cutting at speeds up to 20,000 frames per second.
The team discovered that onion droplets form through a two-stage process: an initial violent ejection driven by internal pressure, followed by slower fragmentation of liquid streams in air. Blunter blades create up to 40 times more droplets because the onion’s tough outer skin acts as a barrier, allowing the softer interior tissue to compress significantly before rupturing and releasing pressurized liquid.
The research reveals that droplets are ejected at speeds between 1 and 40 meters per second, with the fastest ones posing the greatest risk of reaching a cook’s eyes. Beyond tear reduction, the study suggests sharp knives may also limit the spread of foodborne pathogens, since atomized droplets can carry bacteria like Salmonella from contaminated cutting boards.