Tears in the Kitchen by Cutting Onions

Cutting onions often results in tear-inducing aerosols, yet the underlying droplet formation mechanisms have remained unclear. Using high-speed imaging, we reveal a two-stage ejection process: an initial rapid burst followed by ligament fragmentation. By systematically varying blade sharpness and cutting speed, we show that more blunt but faster blades significantly increase both droplet count and ejection energy. Strain mapping indicates that the onion's tough epidermis acts as a protective shell, allowing the softer inner mesophyll to compress substantially before rupture. To explain these observations, we developed a simplified bi-layer model and validated it through both theoretical predictions and mechanical testing, with critical fracture forces. Our findings show the importance of blade maintenance not only for cutting efficiency but also for reducing aerosolized droplets.