When you cut an onion, it releases volatile sulfur compounds that escape into the air. These compounds then react with the water present in our eyes to form sulfuric acid, irritating our eyes and causing tears to protect them.
The onion is primarily composed of water (about 90%), but what interests us most here is sulfur. The onion contains compounds called amino acid sulfoxides, stored in its cells. As long as the cells remain intact, there’s no problem. But when you cut or crush these cells, these sulfur compounds come into contact with an enzyme, alliinase. And that’s when it starts to get complicated for your eyes. The ensuing chemical reactions produce volatile and irritating molecules, such as the famous propanethial oxide, which is directly responsible for your tears.
The onion contains cells filled with sulfur compounds, notably cysteine sulfoxide. When you cut into the onion, you break these cells. Some enzymes, called alliinases, which were quietly sitting in their corner, come into contact with these sulfur compounds. This encounter triggers an immediate chemical reaction that transforms the compounds into an irritating gas: the famous propane-thial oxide. This volatile gas rises directly to your eyes and comes into contact with the water present on their surface. This produces a small amount of very dilute sulfuric acid, but enough to irritate your eyes. As a result, your eyes immediately send an alarm signal to your brain, and the tear glands produce tears to flush out the intruder.
When the eyes feel irritation, they trigger an automatic reflex: the tear glands produce more tears. This natural mechanism allows for the rapid elimination of the irritating substance, in this case, the gas released by the cut onion. As a result, our eyes become all wet to protect us by washing the surface of the eye and quickly flushing out the bothersome chemicals. Not practical for cooking, of course, but very useful for protecting our precious eyes in everyday life!
Not all onions clearly have the same power to make you cry! Classic yellow onions are generally the champions when it comes to tears, as they contain much more irritating substances. In contrast, you'll cry less when chopping red or white onions, which are much less aggressive due to their lower content of pungent sulfur molecules. And when it comes to being gentle on your eyes, sweet onions, like those from the Cévennes or Vidalia, are surely your best friends: almost no tears guaranteed, thanks to a minimal concentration of irritating agents. They are truly a delight.
To cry less when cutting an onion, you should mainly avoid letting the irritating gases reach your eyes. A simple trick is to wear glasses (swimming goggles or regular glasses work quite well). Also, use a sharp knife, because a sharp blade crushes fewer cells and therefore releases fewer stinging enzymes. Another solution: put the onion in the cold (fridge or freezer for a few minutes) just before cutting it; this slows down the release of the irritating gases. You can also cut the onion under a stream of cold water; the water will carry away some of the gas before it reaches your eyes. Finally, cutting the onion near an exhaust hood or an open window significantly reduces the concentration of the irritating gas in the air.
Some professional chefs recommend cutting onions under a stream of cold water or near an exhaust hood to minimize the irritating impact of the gases on the eyes.
Swimming or safety goggles may seem ridiculous in the kitchen, but they are extremely effective at preventing you from crying while cutting onions!
Red onions generally contain more sulfur compounds than white or yellow onions, which often makes them more irritating to the eyes.
The sulfur compounds responsible for tears can also stimulate the tear glands to trigger the production of tears that are beneficial for naturally cleansing and protecting the eye.
Yes, placing the onion in the refrigerator for about 30 minutes before cutting slows down the release of volatile irritating compounds. These then pass less easily into the air, thus significantly reducing the irritating effect on the eyes.
These special glasses have seals around the eyes that prevent irritating compounds from reaching your eyes. They are indeed very useful and significantly reduce tears while cooking.
Yes, the onion varieties referred to as "sweet" or "mild," such as red onions or scallions, generally release fewer irritating compounds and are therefore less likely to cause tears when sliced.
Cutting onions under water or under a thin stream of water helps to immediately dissolve the irritating compounds produced, thus limiting their diffusion into the air and significantly reducing tearing. However, this method makes cutting a bit more difficult, so its practical usefulness is limited.
The sensitivity to the chemical compounds released by onions varies greatly from person to person. Some individuals have more reactive tear glands or greater sensitivity in their eyes to these irritating compounds, which explains why they cry more than others.
No one has answered this quiz yet, be the first!' :-)
Question 1/5
