The crocodile tears shed over chopped onions has been used to evoke laughter in the audience in many movies. Comedy, it may be in movies but in reality it is a source of discomfort to the person slicing the onions. The stinging sensation in the eyes and the runny nose make one wonder if it is a veggie or some tear gas grenade in disguise. Some dismiss this topic as trivia, some submit to the suffering without much fuss thinking it is inevitable and still other smart ones delegate the troublesome task to others 😉 This problem can be easily resolved if we understand the science behind the smarting sensation. Here is what happens:
- When we cut an onion, its cell walls get torn and release an enzyme called Lachrymatory-factor synthase into the air.
- The synthase enzyme converts the sulfoxides (amino acids) of the onion into sulfenic acid.
- The unstable sulfenic acid rearranges itself into syn-propanethial-S-oxide.
- Syn-propanethial-S-oxide gets converted into sulphuric acid when exposed to oxygen in the air. Now, when the acid comes in contact with our eyes, the lachrymal glands get irritated and produce tears.
So, the secret to a pleasant onion-chopping experience lies in reducing the amount of sulphurous gas released into air, either delaying its release or diluting it and protecting our eyes from its impact. Though there have been numerous methods revealed by experts around the world to combat this problem, I would like to state the most easy and practical ones here.
- Leave the root end intact till the last cut as this is where the synthase enzyme is most concentrated.
- Use a very sharp knife and cut quickly. This crushes less number of cell walls and causes a minimal amount of the gases in the onion to be released.
- Chill the onion in the refrigerator for ½ -1 hour before you slice it. The cold temperature slows the movement of atoms in the gas so that they do not float up into the air so quickly.
- Cut the onion into half, peel the outer skin, rinse it in running water and then cut. This dilutes the gas before it floats into the air. If they are shallots, soak them in a bowl of water for ½ hr and then cut them one by one.