Suggestions to avoid the dreaded onion-induced tears in the kitchen run the gamut of ideas—from freezing them, to cutting them underwater, to sporting special goggles, to even stuffing some bread in your mouth beforehand. But what’s the actual science say about how to escape your next onion encounter unscathed? According to a team of physicists at Cornell University, it’s all about the sharpness of your weapon of choice and your speed of approach. Their findings are laid out in a preprint study—and it even involves a tiny onion guillotine.
Onions have been an agricultural staple as far back as at least 3000 BCE. Ancient Egyptians actually revered them as representations of eternity due to their concentric inner layers, and would place the vegetables in the tombs of pharaohs. Apart from their spiritual use, onions also have very clear health and medicinal benefits, particularly when it comes to their nutritional, antioxidant content, and antibacterial properties.
But after over five million years of use around the world, the fact remains that one onion compound in particular still poses a problem for our eyes: syn-propanethial-S-oxide. The chemical is released in the sulphur-rich spray that accompanies dicing the vegetables, which then travels through the air and eventually comes into contact with your tear ducts.
To test the dynamics of these aerosols and how to best avoid them, the Cornell researchers set up a small guillotine outfitted with various steel blades before coating onion quarters with black spray paint. This wasn’t to establish a more funereal mood in the lab, but instead to help the team track the onion’s deformation in response to the blade. After using an electron microscope to measure the blade tip’s width (which varied between 5 and 200 millimeters), they commenced slicing at speeds between 1.3 and 6.5 feet per second (or 0.4 and 2 meters per second). But no word of if that could match the current Guinness World Record for most onions peeled and sliced in a minute–21.69 ounces.Â
Their recordings clearly showed that sharper blades offered fewer droplets traveling with less energy. The duller the blade, the more it was liable to bend the onion’s skin before cutting. These delays stored elastic energy that built up pressure in the vegetable before ultimately slicing open, resulting in a more explosive release of juice. In some cases, the aerosol particles reached speeds around 141 feet per second. To make matters worse, those droplets fragmented while flying through the air to create an even more diffuse mist of all-natural mace.
Dull knives can be such a nuisance that they even create as much as 40 times as many droplets as a sharper alternative. Meanwhile, faster cutting speeds generated four times as many particles as slower rates.Â
The data from this preprint still needs to be peer reviewed. Yet from this research it seems pretty clear that a sharp knife and a slow approach will most consistently minimize the undesirable effects of onions. What you do with all those sliced bits, however, is totally up to you.
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