Onions. The only vegetable that will exact revenge upon you for cutting it...

^Source

All you wanted was to add some flavor to your meal, and now you find yourself in the kitchen weeping like you just got inducted into the culinary hall of fame...

Everyone knows onions make us cry when we cut them, but do you know why? In this installment of Super Cool Science S#!t, I'll not only explain what causes them to make us cry, but how you can prevent it from happening, so your roommates will stop asking "Why are you crying, bro?"

Onions are plotting your demise from day one...

They almost know they're going to be mutilated for some human's dinner, so as they're growing, they absorb lots of sulfur from the soil. They use this sulfur to produce amino acid sulfoxides, and when you cut, crush, or peel an onion, these amino acids, along with enzymes called lachrymatory-factor synthase, are released into the air and react with one another, creating Sulfenic acid...

syn-propanethial s-oxide.png
syn-Propanthial-S-oxide (C3H6SO)

Sulfenic Acid is a very unstable molecule, and while airborne, rearranges into the more stable syn-Propanthial-S-oxide, pictured on the right. This is the bad boy that gives onions part of their scent and flavor, as well as causing your eyes to fill up with water so you aren't able to see. The onion hopes that this effect will cause you to miss you next slice, cutting yourself instead. When "syn-P" reaches your eyeballs, it's game over! This chemical acts as an irritant, and it causes your lacrimal glands to trigger, releasing tears to wash away the annoying gas that is now in your eyes.

For your entertainment, here's a hilariously awkward explanation of the process from the Youtube channel, Stuff You Should Know, from their series 'Don't be Dumb':

So how do you stop it?

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Many people have put forth many theories as to how to prevent the irritating gas from reaching your precious eyes. Some work, some don't. I didn't test any myself, because I hate onions, and didn't want to both cry and vomit in the making of a Steemit post... I ain't makin' that much :)

Marygrace Taylor over at Greatist did, though. She tested seven different suggested methods, and found that a few of those methods actually worked to prevent her from crying, like getting the onions incredibly cold, even freezing them, and holding a piece of bread in your mouth!?!? That last one piques my interest, and the next time I'm cutting an onion, I'll definitely have to try it... It's supposed to help absorb some of the gas that gets formed in the air...

Some methods that I personally know work are:

Using an incredibly sharp knife.
A sharper knife minimizes cell damage, which minimizes the amount of enzymes that get released from the onion.
Cutting the onion under water.
This can cut the tears by not letting the enzymes from the onion get into the air at all. The syn-P reacts with the water, which creates a barrier between the onion, and your sensitive sight organs.

And my personal favorite:

Using goggles!
Grab your spare lab goggles and you'll never fear another onion again! Are you not a cool scientist with lab googles?

^{This is a real thing on amazon for $20... Source}

You can get these swanky "onion-cutting goggles" that will make you laugh instead of cry, as you slice-n-dice those onions in style.... or something like that. Regardless of their appearance, they work by using a layer of foam to create a barrier around your eyes, preventing any gas that wafts by from getting into your eyes. Don't have $20, but still want to look silly and be safe in the kitchen? Wear a cheap pair of swimming goggles... If they can keep the water out of your eyes, they can prevent you from crying when you're dealing with onions.

Don't be afraid of onions! Knowledge conquers all!

Now that you know that onions spray their juice, which mixes with the air and changes into an acidic gas, which gets into your eyes, makes you cry like a baby, you can arm yourself with a sharp knife, eye-armor, and science, to claim victory over this onerous vegetable every time you encounter it.

References:

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Ready to learn more? Check out my last Super Cool Science S#!t post, about the most explosive chemical man has ever created, Azidoazide Azide!

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Super Cool Science S#!t # 18 - I'm not crying, bro! It's these damn onions!