How Often Should You Sharpen Your Knife? Use an Onion to Find Out.

If you’re like us, you use your knives every day. Here’s a trick for knowing when it’s time to sharpen them.

Published May 16, 2022.

Let’s face it: All knives get dull over time. It doesn’t matter what kind of metal the blade is made from or what style of knife it is. If you use it regularly, it will eventually lose its keen edge. And there’s nothing more annoying than a dull blade. It’s a pain to use, and worse, it’s unsafe, as it can slip more easily than a sharp blade, putting your fingers at risk.

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So how do you know when its time to sharpen your knife? As the main knife tester on the review team, I get this question a lot. In the test kitchen, we usually recommend something called the paper test. In it, you use your knife to slice through a single sheet of printer paper or newspaper. If the blade drags on the paper, cuts ragged lines, or refuses to cut cleanly at all, it’s time to touch up the blade. It’s also useful to perform this test after sharpening your knife to see if it’s sharp enough. 

But there’s a simpler way. All you need to do is pay attention while performing a simple task that you probably do multiple times a week: dicing an onion


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Sharp knives will slide effortlessly through the onion, making quick work of the task. Dull knives will make the process a chore: You’ll find that you need to use more force to drive the blade through the onion, and your cuts will be less even and easily controlled. Even if you’re new to cooking, it’ll be hard to mistake the signs of a dull blade as you dice. 

Just open your senses and it’ll be clear. You’ll hear a dull blade crunching through the onion instead of silently gliding through it. And as your dull blade bruises and ruptures more of the onion as it makes its reckless way through it, you’ll both smell more onion and feel your eyes stinging and watering even more than they might ordinarily. (You’ll need to ditch the onion goggles for this test.)

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Fortunately, if your knife is dull, it’s not hard to hone and sharpen your knives. We have a whole guide to honing and sharpening! Whether you use a honing rod, a whetstone, a manual sharpener, an electric sharpener, or even a professional sharpening service, there are lots of good ways to get your blade back into fighting form.

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