Ever start tearing up when you cut an
onion? I do. Most people do. When I was a little child, I rubbed my eyes once and
then I burst into real tears. Sorry, Mom,
I will leave you alone with those onions. Bye! Well, why do onions make you cry? Do
onions really make us cry? I’m not really sure. Yet I do believe there is
something with onions that bring tears to our eyes when we cut them. And it was
nothing to do with their strong smell or our olfactory nerves.
When you cut into an onion, it simply releases
a strong sulphur
compound that wafts toward your eyes. When the gas reacts with the
moisture in your eyes, it begins to burn, creating those infamous “onion tears”. This sulphur compound in the onions also leave a typical
odour of onions on your hands even after washing.
Scientifically speaking, onions
contain amino acid sulfoxides that form sulfenic acids in the onion
cells. Both the enzymes and the sulfenic acids are kept separately in the
cells. When you cut the onion, the otherwise separate enzymes start mixing and
produce propanethiol S-oxide, which is a volatile sulphur
compound that
starts wafting towards your eyes. The gas that is emitted reacts with the moisture in your eyes and forms
sulphuric acid. The sulphuric acid thus causes burning sensation in your eyes
and this in turn leads to the tear glands secreting tears. Thus you end up with
watery eyes every time you cut onions.
So, is there any way to keep us from
tearing up?
Yes.
1. Use
a very sharp knife when cutting onions.
The enzymes are released when the onion cells are broken or crushed.
Using a sharp knife will slice
through the onion rather than crushing and thus, fewer enzymes are released.
2. Chill
the onions in the freezer for 10-15 minutes
before cutting them. This reduces the amount of the
acid enzyme released into the air and has zero effect on taste. The fridge can
do it, too; just make sure not to keep them next to apples or potatoes,
or leave them in there for too long (20 minutes should do it) as they can cause odors if you do.
3. Cut
the onion under water. This
is an effective method, but the problem is that it is a
bit difficult to maneuver. In the water, the onion bits go everywhere unless
you hold onto them and then scooping them up and draining out the onion water.
4. Cut
the onion near hot running water or a cloud of steam. Steam from a kettle or pan of water will do the trick.
The science here is that the steam will draw out the vapors from the onion,
dissipating them.
5. Breathe
through your mouth and stick your tongue out. This
draws the gas over your wet tongue. The olfactory nerves, which are closely
located to the tear duct nerves, will be bypassed and there will be no tears
generated.
6. Soak
the onion in water. The enzyme is denatured by the
water-air boundary. However, it eliminates some flavor and the onion
will be a little more slippery than normal.
7. Point
your knife away from the tubes. Pointing the tubes away from you while cutting will keep the
onion from spraying in your eyes. Pay
attention to air currents too as a breeze
of any kind can send the spray toward your eyes!
8. Whistle
while you work. Whistling makes a significant
airflow, specifically away from your face, which keeps the onion mist away from
your eyes.
9. Stick
a piece of bread in your mouth. Many
people report that chewing, especially bread, helps avoid tears when cutting
onions. Chew very slowly. Your mouth will water, but your eyes won't!
Now you know why onions make
you “cry” and how to avoid tears when cutting onions.
***
Photo credit: Bibi / Foter / CC BY-NC-SA
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