The best way to chop an onion

Onions form the base for many recipes, but every time you chop one up a stream of tears blinds your eyes - read some tips for avoiding this peril!

Whether you’re making a curry, a stiry-fry, a simple spaghetti bolognese or something a little more exotic, the chances are you’ll be required to chop an onion for the recipe. But, if you’re anything like me, it seems as soon as the knife goes anywhere near the bulb, the waterworks switch on and before I know it, I’m barely able to see and my eyes are stinging.

Hardly the best condition to be in when wielding a sharp knife.

Chopping onions makes you cry because, when you cut into the onion, you break into its cells, allowing the onion’s enzymes to mix with its naturally formed amino acids. This creates the sulphur compounds (which cause the characteristic odour to stay on your fingers) and a gas called propanethiol S-oxide (doesn’t exactly trip off the tongue does it?).

When this gas reacts with the water in your eyes, it forms sulphuric acid, which burns, causing more tears, which – you’ve guessed it – can create more acid. It’s like a chemistry lesson in chain reactions, right there in your kitchen!

The problematic enzyme is ‘de-activated’ when you cook the onion, so the smell or gas emitted from the cooked onion doesn’t burn your eyes. Following this logic, in 2008, scientists managed to genetically engineer an onion without the enzyme required for causing tears. But who wants to eat a genetically engineered onion?

What else can you do to avoid the pain? Over the years, I’ve heard plenty of tips, old wives tales and crackpot theories on the best way to prevent this from happening. Some work better than others and, in my experience, different things work for different people.

So here’s a few tactics for you to try – let us know how you get on in the comments box below, as well as if you have any of your own suggestions.

Wear swimming goggles

If there’s one thing guaranteed to have you looking like a prat in the kitchen, it’s prancing around with swimming goggles on. But since there’s a barrier between your eyes and the offending onion, it’s pretty much impossible to be affected. Some people even go to the lengths of having a pair hanging up in their kitchen.

I’m also told that people with contact lenses very rarely cry when chopping onions – next time you’re at the opticians, think about that as a reason to go for lenses.

Effective rating: 9/10 (minus one point for the silliness factor)

Chop near a running tap

Since the tear-inducing gas reacts with water, if you can position your chopping board close enough to a running tap then you may be able to prevent the acid reaching your eyes. In practice this isn’t 100% effective and you might think it a bit of a waste of water if it takes you a while to chop. An alternative is to stick your tongue out while chopping, but this seems to be even less effective than the tap and you’ll end up looking a bit silly.

Effectiveness rating: 5/10

Hold a teaspoon in your mouth

One of the bizarrest methods I’ve heard, but also one of the most common. Nobody seems to have any idea how it works, but it’s pretty simple. Hold a teaspoon in your mouth for the duration of the chopping time. Again, this isn’t one for those who care about looking stylish in the kitchen but if it works, it works. In practice, I’ve found that this does work, some of the time. Why not combine it with the swimming goggles and running water methods just to be extra sure though?

Effectiveness rating: 4/10 

Chop with wet hands

This works in the same way that chopping an onion near a running tap does, the enzymes are drawn to the moisture on your hands, instead of your eyes. I’ve also found it works better if you wash the onion too. Again, not a foolproof method but one that is quick and easy to do – and has the added bonus of not making you look silly.

Effectiveness rating: 6/10

Store the onion in the fridge

Again, this isn’t 100% effective, but it can help. Because the onion is cold, the enzymes inside the onion are slower to mix with the acid and the gas is slower to react. But it’s inconvenient to take up valuable fridge storage space with onions that could easily go in a cupboard, and it doesn’t always work, particularly with large onions.

Effectiveness rating: 7/10

The no-tears chopping method

In my opinion, by far the best way to prevent crying is to learn how to chop an onion properly in the first place.

It’s a little tricky to master, but it’s worth the practice. You’ll want to use a very sharp knife, and if you haven’t stored the onions in the fridge then at least chill them before you chop them.

The bit you want to avoid chopping is the root, or the ‘hairy’ part of the onion, as this is where those pesky enzymes are released from.

First, peel the onion. Start chopping at the opposite end to the root, slicing until you get very close to it. Discard the root and turn the rest of the onion round and make slices again – you should end up with little squares, perfect for most recipes.

Of course, it can still go wrong and you’ll feel that familiar stinging in the eyeballs – perhaps it’s best to have those goggles on standby after all.

Effectiveness rating: 8/10

Also worth your attention:

Bill Granger’s buffalo rendang

The secret to cooking perfect rice