Onions are a staple in many diets, whether they’re fried, grilled, caramelized, or raw.
But its desirable flavor comes at a price, as those who chop onions suffer constant tears. But why does chopping onions make you cry?
The culprit is called a tear agent, which is a chemical that irritates the eye. When the onions are intact, a group of compounds called cysteine sulfoxides are separated from an enzyme called allinase. But when onions are cut into slices or cubes, the barrier between the compounds and the enzyme is broken. The two combine, resulting in a reaction: allinase causes cysteine sulfoxides to convert to sulfonic acid.
“Sulfonic acids are not very stable, so they have to be converted into something else,” said Josie Silveraroli, Pharm.D., candidate at Ohio State University and first author of a 2017 study in the Journal of the American Chemical Society ACS Chemical Biology on lacrimal factor. In onions, sulfuric acid has two options: the first option is that it can spontaneously condense, reacting within itself, and become an organic sulfur compound, which gives the onions their strong smell and flavour. A similar reaction occurs in garlic, Silveroli said, which is why it also has a pungent flavor.
But the second choice of sulfonic acid is unique to onions and another couple of alliums, or a genus of flowering plants that produce vegetables such as onions, garlic, scallions, and leeks. Another enzyme, tear factor synthase, which was hidden in the cell, plays its role and rearranges the lacrimal factor sulfonic acid.
Silveraroli said the tear agent is a volatile liquid, which means it turns into vapor very quickly. Thus, it reaches your eyes and irritates the sensory nerves. “Your eyes begin to tear to get rid of irritants,” he added.
He explained that it is possible that both the organosulfur compounds that give onions their intense flavor and the tear factor evolved as defense mechanisms. Their purpose is to stop insects, animals, or parasites that may harm the onion plant.
And if the tears shed are more than you can handle, you have options. Bon Appetit recommends wearing goggles or a face shield to protect your eyes. It may also help to use a sharp knife, which damages fewer cells and creates less “tear gas” than a regular knife.Why Does Chopping Onions Make You Shed Tears ?