Saed News: If your eyes water while chopping onions, physicists have proposed a possible solution, although it is unlikely that professional chefs will approve of this method.
According to the Science and Technology Service of Saed News, when onions are cut, sulfur-rich compounds are released into the air, one of which is "syn-propanethial-S-oxide," a chemical that irritates the nerves of the eyes and causes tears.
Sanghwan Jung and his colleagues at Cornell University in New York used high-speed cameras to study the spray of chemicals released from cutting brown onions with blades of varying thicknesses and at different speeds.
Jung and his team used a guillotine equipped with a thin steel blade dropped from above to cut a quarter of an onion coated with black spray paint. This allowed the researchers to precisely observe the onion’s deformation and record particle spray with high-speed cameras. Using an electron microscope, they measured the blade tip width, which ranged from 5 to 200 micrometers, and adjusted the blade height to control cutting speeds from approximately 0.4 to 2 meters per second.
Results showed that sharp blades caused fewer droplets to be dispersed at lower speed and energy. However, when an onion is cut with a dull knife, its skin bends, storing elastic energy and increasing internal pressure. As a result, when the onion skin bursts, it does so explosively, scattering some particles at speeds up to 40 meters per second. These droplets may break apart further after entering the air, producing even finer particles.
Researchers found that a dull knife can spread up to 40 times more fine droplets compared to a sharp knife. Also, when cutting speed is high, the number of dispersed particles is four times greater than at lower speeds.
If you cut an onion slowly with a sharp knife, the chance of irritant compounds reaching your eyes is lower; however, Jung and his team did not test this hypothesis experimentally.
Anne Joll from the University of Manchester says cutting seems simple because we do it daily, but in reality, the process depends on very fine, atomic-level scales. She adds, "It’s not clear to me that this will make a big difference in the kitchen or have any significant practical application."
