Have you ever been chopping an onion and the tears start to flow? There are plenty of cooking hacks out there claiming to keep you from crying while chopping onions, but the reason those tears form in the first place might be a dull knife.
Chopping an onion with a dull knife can cause onions to emit a stronger odor alongside the chemicals that make you cry.
If you’re trying to dice an onion with a dull knife, you’ll actually hear the blade as it slices through. If your knife is sharp, it will glide through the onion with ease and you shouldn’t hear much of a crunch—except your blade gently hitting the cutting board.
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So how does a dull knife cause more onion tears? That crunch you hear is actually the onion getting ruptured and bruised by the knife. When your knife cuts through so harshly, enzymes and sulfenic acid combine to create more propanethial S-oxide, the gas that makes you cry.
Thankfully, sharpening knives is easier than you might think. You can use a whetstone, a two-sided knife sharpener, or even take your knives to a professional once or twice a year to get them razor-sharp.
If you haven’t been sharpening your knives, now is the time to do it. You’ll feel a difference in your prep work and chopping onions might end up becoming one of your favorite kitchen tasks.