If you plan on making a salad, or some kind of soup or a savory stir-fry, onions will most likely be part of the equation. You might also slice them into rings to place on sandwiches, or sauté them gently until they’re soft, translucent, and absolutely delicious. But something else may be likely as well: When you’re cutting or chopping them before you get very far into the first onion, you’re likely to find your nose twitching and tears making your eyes red. Why would onions makes us cry?
You know that familiar feeling: tingly, stinging eyes, followed by tears. Why would the humble onion, a key ingredient in your next culinary creation, cause you such discomfort? Why do onions makes us cry?
As Eric Block, author of the book Garlic and Other Alliums explained to NPR, “the onion is a perennial bulb that lives in the ground with lots of critters who are looking for a snack.” And so they have a chemical defense system, which, like a skunk fending off predators with a stench, releases the tear-jerker chemical to protect itself from being eaten. Within each cell of an onion is a sealed vacuole filled with enzymes that rupture when cutting into. The enzymes then mix with other chemicals in the onion cell and, in Blocks words, “a whole cascade of chemical processes happen within an instant.”
The result of all those chemical processes is syn-propanethial-S-oxide molecules, the irritating culprit making you cry. Every time you cut an onion, you are being subjected to a chemical attack. This is why onions makes us cry.
While in the soil, onions absorb sulphur from the earth. This enables them to create a volatile class of organic molecules known as amino acid sulphoxides.
When you cut an onion, the cells break open and a number of reactions take place – enzymes convert the amino acid sulphoxides into sulphenic acids, which then reform into a volatile gas called Syn-Propanethial-S-oxide. The gas is released into the air and eventually reaches the surface of the eye, where it stimulates sensory neurons, hence the stinging sensation. That stinging sensation makes us cry.
The eye reacts by producing tears to dilute and remove the irritant. If you want to tone down the waterworks, try refrigerating the onion or running it under cold water before cutting it. The cold temperature will slow down the chemical reaction.
The best strategy to avoid tearing up, Block says, is to chop onions in a well-ventilated area, near a fan. “If you just cut the onion in a stream of air blowing away from your face,” he says, “then you’ll pull the molecules away and they won’t get to your eyes.”
Refrigerating the onions for a few minutes before chopping can help as well, he notes, since the volatile compounds that cause eye irritation “are less volatile when they’re cold.”
It’s virtually impossible to avoid watery eyes entirely when you’re cooking with onions. The next time you are getting your chopping board ready to whip up a meal full of healthy onions, think of refrigerating it, that will help not to make your eyes teary. Want to share measures to avoid watery eyes? Let us know in the comments below.