Because a sharp knife is a safe knife.
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It might sound backwards, but a sharp knife is safer than a blunt one. A sharp chef's knife will cut quickly and more precisely through meat and veggies, making it less likely to slip or bounce off the ingredient and into your hand. Similarly, a sharp utility knife will cut through cables, plastic and other materials easier, making it more useful.
Sharpening a knife isn’t difficult. It requires just a few minutes and one tool: a whetstone. In this guide, we're covering flat-bladed knives—for instance, the chef’s knife that's commonly used in the kitchen. If you want to sharpen a serrated or rough-edged knife, you'll want to invest in a good knife sharpener.
To sharpen a flat-blade knife, you will need a whetstone, a special type of stone that's abrasive, with a rough surface that removes microscopic pieces of metal from the edge of a knife to create a sharp, clean edge. While you do need to wet the stone before you use it, the name actually comes from the old English word "whet," which means sharpening. So, a whetstone is a sharpening stone.
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You'll notice whetstones have a rating called grit, which refers to the size of its microscopic stone particles. The higher the number, the smaller the particles and the less metal they'll remove when used, creating a finer and, thus, sharper edge. Most whetstones are actually made of two stones combined into one—a low grit stone and a high grit stone. As you may have guessed, one side is for the first coarse pass on a knife, while the other is for the second finer, more precise pass.
To prepare the whetstone, immerse it in water for 10 minutes, then take it out and put it in the holder, with the coarse side up. If the stone didn’t come with a holder, put a towel on a flat surface and put the stone on that, so it won’t slide around while you're using it.
Dribble water on the stone until it sits in pools. This water keeps the stone lubricated and helps the knife glide over the surface.
Next, pick up your knife and hold it with the sharp edge facing away from you and one of the flat sides on the stone's surface. You'll want to hold it with your thumb on the blunt edge and an index finger on the flat surface—see the image above for an example.
Lift the back of the knife up slightly so that the knife is tilted, which puts the angled cutting edge against the whetstone surface. To make sure the cutting edge is flat, carefully put your finger on the knife and run it off the edge onto the stone. When you find the right angle, you'll barely feel a gap between the two. One chef I know also teaches the trick of stacking up three pennies and putting them under the blunt edge of the knife to find the right angle.
Be careful when doing this, and don’t run your finger from stone to knife, as you could cut your fingertip, which hurts a lot—take my word for it.
Hold the knife at this angle and slowly pull it toward you and across the stone in one smooth motion, so the entire cutting edge from hilt to tip is dragged across the abrasive surface. Turn the knife over and drag it away from you and across in the other direction so the other side of the cutting edge is dragged over the stone. The entire move is like drawing an X: One up-down stroke on one side of the blade, one down-up stroke on the other. Repeat this move five times.
Turn the stone over to the fine side and wet the surface to keep everything lubricated. Repeat the same motion at the same angle five more times to give the knife the clean, sharp edge you need.
Never push the knife over the stone—that will ruin the edge. Don’t press the knife down on the stone, either. Simply hold the knife steady and let the weight of the tool do the work.
Finally, wipe the knife and whetstone off with a paper towel or cloth to remove the microscopic pieces of metal that will have been shaved off the blade.
Once you're done, the knife should have a clean, sharp edge that will slice through meat and veggies with ease. You can test it by holding up a piece of paper and carefully slicing down from the top. A properly sharpened knife will cut through the paper without stopping, while a blunt or damaged knife will stop, crinkle the paper or struggle to cut parts of it.
Now that you know how to sharpen a knife properly, you have no excuse for wielding dull, unsafe implements in the kitchen.