A team of physicists, biologists and engineers at Cornell University, in the U.S., has discovered some of the factors that lead to more or less spray when cutting onions and found a couple of ways to reduce the amount of eye irritation. The group has published a paper describing their study on the arXiv preprint server.

Prior research has shown that eye irritation when cutting onions is caused by the release of syn-propanethial-S-oxide into the air along with other juices in the onion. For this new study, the team in New York wanted to know what factors led to more or less of the juices being spewed into the air during slicing.

To find out, the research team outfitted a special guillotine that could be fitted with different types of blades. They also coated onion chunks with paint to allow for better viewing of the cutting process. They used the guillotine to cut samples, each of which was recorded. Trials varied knife size, sharpness and cutting speed. They even used an electron microscope to accurately measure the knives before use.