From fresh salads to hearty stews, onions are a key ingredient in many dishes. They are loved for their natural sweetness and are used in classic kitchen staples like pasta sauce and Asian stir-fries. The humble yet versatile onion can even be separated into rings and dipped into the batter to be deep-fried into onion rings, or caramelised and served in sandwiches and burgers.
But there is one other thing that onions are notorious for – bringing people to tears. Slicing a large batch of onions often leaves the regular home chef with painful eyes and wet cheeks. Sometimes, the slicer-in-charge has to take a break and even step away from the kitchen to escape the pungent fumes emitted.
Their potency varies across types. Yellow onions with brown skins are the most villainous of them all, while red onions come in second. Fortunately, white onions and shallots don’t lead to much tear-shedding.
What makes onions such powerful tearjerkers?
Onions are part of the allium group of plants, which includes: shallots, garlic, chives and leeks. They derive their taste from the sulphur content in soils. Milder onions, such as the white varieties, are grown in lower-sulphur soils for a less pungent smell and taste.
What gives onions the ability to make you cry more than having a broken heart? Onions contain a chemical called lachrymatory-factor synthase, which is released into the air when the onions are cut. Then comes a millisecond-long chemical reaction that sees the synthase converting the natural sulfoxides amino acids into sulfenic acid.
The sulfenic acid’s molecular structure is unstable, and when exposed to the air, it rearranges itself into syn-ropanethial-S-oxide. This particular compound irritates the larymal glands in your eyes, which causes them to sting and water!
Luckily, the reaction that causes your eyes to tear up and hurt lasts about 30 seconds. Which isn’t that much of a problem if you only have a single onion to chop.
The best methods for cutting onions (no goggles required)
What if you are preparing dinner for 10? When you’re preparing a meal for more, it naturally comes a bagful of onions to go through? The easiest way to eliminate tearing is to cut the onions with a sharp knife. By cutting them as cleanly and as quickly as possible, it reduces breakage of the flesh, thus lowering the amount of chemicals released. This is also a compelling reason for homemakers to sharpen their knives frequently.
If you are new to cooking and are intimidated by sharp knives, or you just want to play it safe, here are some methods to make slicing onions more bearable. Don’t worry, you can leave your swim goggles in your closet.
1. Chilling onions in the refrigerator
Refrigerate your onions ahead of time. The cold temperature minimises the reactivity of the chemicals in the onion when it is cut. Onions warm quickly outside of the refrigerator, so chop them fast. You could also freeze your onions, but condensation that forms on their skins after you take them out of the freezer makes them slippery and harder to handle.
Onions dislike moisture. While onions don’t spoil that easily in cooler climates, they tend to rot faster in humid environments. In households where the climate is hot and humid, it is common to see onions and garlic being kept in well-ventilated baskets, suspended above kitchen counters and away from the sink. So it makes sense to store your onions in the refrigerator.
2. Rinse them in cold water before food prep
This method is also effective as the cold water chills the onions and reduces the reactivity of their chemicals, but the downside is it washes away some of their flavours. You could use this method if you are not fussy about retaining the full flavour of your onions. This also works great for those who don’t store their onions in the refrigerator or need to prepare their meals right away.
3. Run the vent while cutting onions
Leaving the vent on sucks away all the nasty gases that are released from the onion when you cut it. If you don’t have a vent, use a fan. Just make sure the wind blowing from the fan is directed away from you, not towards you!
4. Use a food processor or a mandoline
A food processor or a mandoline is a great investment for those who hate the tears that onions bring. It also saves lots of time and effort for the home chef. The only downside of the food processor is that it chops the onions too roughly.
If you want to make onion rings or if your recipe requires you to slice them finely, you should use a mandoline instead. Just be careful of the sharp blades of the mandoline when you are down to the ends of the onion – you want sliced onions, not sliced fingertips!