Cutting onions is a common task in the kitchen, but it often comes with an unpleasant side effect: burning and watery eyes. Why does this happen, and what can you do about it? The answer lies in the onion’s chemical makeup and how it reacts when damaged.
The Science Behind the Tears
Onions contain a chemical called syn-propanethial-S-oxide. When an onion is cut, cells are broken, releasing enzymes that convert amino acid sulfoxides into this volatile sulfur compound. Syn-propanethial-S-oxide is a lachrymatory factor (meaning it causes tears) that becomes airborne and irritates the lachrymal glands in your eyes. This irritation triggers your tear ducts to produce tears in an attempt to wash away the irritant.
The aforementioned “suberin,” mentioned in some sources, is actually a complex polymer found in cork tissue and plays a role in protecting plants. While onions do contain similar fatty acid chains and aromatic compounds, syn-propanethial-S-oxide is the primary culprit for eye irritation.
Minimizing the Burn
While completely eliminating the tearing is challenging, several techniques can help minimize the effect:
1. Chill the Onion
Freezing the onion for a short period (about 15-20 minutes) before cutting can slow down the chemical reaction that releases syn-propanethial-S-oxide. However, avoid freezing it solid, as this will make it difficult to cut.
2. Soak in Water
Soaking a peeled onion in cold water for 10-15 minutes can help draw out some of the sulfur compounds. Keep in mind that this may also dilute the onion’s flavor.
3. Cut Under Running Water
Cutting the onion under a stream of cold water can help wash away the irritant as it’s released. However, this can be messy and potentially dangerous due to the slippery conditions.
4. Wear Protective Eyewear
Wearing goggles or tightly fitting glasses can create a barrier between your eyes and the irritating fumes. This is arguably the most effective method, though it might not be the most fashionable kitchen attire.
Sharp Knife, Smart Technique
Regardless of the method you choose, using a sharp knife is crucial. A sharp knife creates cleaner cuts, damaging fewer cells and releasing less syn-propanethial-S-oxide. Also, try to cut the onion from the root end last, as this area contains a higher concentration of the irritating compounds.
Conclusion
While the burning sensation from cutting onions might be annoying, understanding the science behind it can help you minimize the tears. By employing a combination of techniques and using a sharp knife, you can enjoy the flavor of onions in your cooking without the watery eyes.
