What is the truth behinds the onions that making people cry? Inside the onion cells there are some chemical compounds that contain sulphur. When we cut an onion, we break the cells, and the chemical compounds are released. The amino acid sulphoxides contain in the onion form sulphenic acids. The enzymes that are kept separate now are free to mix with the sulphenic acids to produce propanethiol S-oxide, a volatile sulphured products, which is released into the air. This product wafts upward toward the eyes and reacts with the moisture in the eyes forming sulphuric acid. The formation of sulphuric acid produces a burning sensation. The nerve endings in the eyes are very sensitive and so they pick up on this irritation and stimulating the eyes to release more tears to wash away the irritant by diluting the irritating acid. So our cry is to keep our eyes protected from the acid. This is marvelous!
To let the onion-dicing less problematic, we can have some tricks. We can chop the onion under cold water. The volatile sulphured compounds will be released but they react with the water, instead of reaching our eyes. Besides that, we can refrigerate the onions for few minutes before cutting it. The cold temperature slows down the chemical reaction of forming the volatile sulphured compounds.
The sulphur-containing compounds also leave a characteristic odor on our fingers. So we may be able to remove or reduce some of the smell by wiping our fingers on a stainless steel odor eater.
