Knife Skills: How to Sharpen a Knife
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There is nothing more frustrating in the kitchen than a dull knife. Not only does it make prep work a chore and your finished product less attractive, it's also downright dangerous. A dull blade requires more pressure to cut into a food, and can easily slip off of a tough onion skin and into your finger. Ouch.
Most home cooks should sharpen their knives at least twice a year, and much more frequently if they use their knives every day. There are three ways to go about it.
Method 1: Use an Electric Sharpener. A good quality electric sharpener is an option, but I strongly discourage their use. First off, they remove a tremendous amount of material from your edge. Sharpen your knife a dozen times, and you've lost a good half-centimeter of width, throwing it off balance, and rendering any blade with a bolster (i.e. most high quality forged blades) useless. Secondly, even the best models provide only an adequate edge. If you don't mind replacing your knives every few years and are happy with the edge they give you, they are an option. But a much better choice is to...
Method 2: Send it out to a professional. This is a good option—provided you have a good knife sharpener living nearby, and are willing to pay to have the services performed. If you plan to sharpen your blades a dozen or so times a year as I do, this can get quite expensive. All but the best pros also use a grinding stone, which again will take away much more material than is necessary from your blade, reducing its lifespan. Want to forge a stronger relationship with your blade? Then you'll want to...
Method 3: Use a Sharpening Stone. The best method by far. Not only will it give you the best edge, it also removes the least amount of material. With a fine enough grit, your knife should be able to take hairs off your arm when you've finished. Additionally—and I'm not kidding about the importance of this one—the act of sharpening your knife will help you create a much stronger bond with your blade, and a knife that is treated respectfully will behave much better for its owner. The only problem? It takes a little know-how.
That's where the following guide comes in. Get yourself some water stones, follow the instructions, and practice. You won't believe the difference a sharp knife can makes in your cooking.
Shopping and MaintenanceWhen buying a water stone, look for a large one, at least 2.5 inches wide by 8 inches long, and an inch in thickness. Stones come in various grit sizes, ranging from around 100 and up to 10,000+. The lower the number, the coarser the grit, and the more material it will take off of your knife.
Bear in mind: The higher the grit, the sharper the edge you will get, but the more strokes it will take to get you there.
I recommend keeping two stones in your kit. One with a medium grit (around 800 or so) to perform major sharpening jobs, and one with a fine grit (at least 2,000) to tune the edge to a razor-sharp finish. For real pros, a stone with an ultra-fine grit (8,000 and above) will leave a mirror-like finish on your blade, but most cooks won't notice the difference in terms of cutting ability.
If you only have the budget or space for a single stone, I'd recommend one with a grit between 1,000 and 1,200. Two-sided stones are also available (coarse and fine grit), but are usually of inferior quality.
You will also need a stone fixer to repair any inconsistencies in the surface of your sharpening stones.
Carefully dry your stones after each use, and store them wrapped in a kitchen towel in a dry, grease-free environment. Oil can soak into the porous material, ruining its sharpening ability (and your chances of ever slicing your onions thin enough for that soup).
And finally, remember to hone your knife on a steel every time you use it. While this process won't actually take any material off the blade, it will help keep the blade aligned, making slicing and dicing much easier.
Step 1: Soak your Stones
When working with water stones, it's essential to submerge them in water for at least 45 minutes before using. If the porous stones are not fully saturated, they will dry out during sharpening, causing the knife blade to catch, and giving your edge nicks and dings. Soak both your stones, and your stone fixer.
Step 2: Set up Your Station
Place your stone on a towel set over a cutting board. Keep a container of water nearby to keep your stone constantly moistened during the sharpening process. The stone should be oriented with the short end parallel to the edge of the counter.
Step 3: Begin First Stroke
Place the heel of your knife on the far edge of the stone, holding the blade gently but firmly with both hands at a 15 to 20 degree angle. Using even pressure, slowly drag the knife over the stone towards you down the length of the stone while simultaneously moving the knife such that the contact point moves towards the tip of the blade.
Step 4: Maintain Angle
Be careful to maintain the 15 to 20 degree angle as you pull the knife across the stone. Pressure should be firm, but gentle. The blade should glide smoothly across the stone as you pull.
Step 5: Finish Stroke and Repeat
Each stroke should finish with the tip of the knife touching the bottom of the stone. Lift the knife, reset the heel at the top of the stone, and repeat.
Step 6: Look for Silty Water
As you repeat the process, a thin film of silty looking water should collect on top of the stone and on the blade. This abrasive liquid will gradually take material off the edge of your knife, sharpening it.
Step 7: Check for Burr
As you continue to repeat strokes on the first time, eventually a tiny burr will form on the other side of the blade. To check for it, place the blade on your thumb, and pull it backwards. If the burr has formed, it should catch slightly on your thumb (with really fine grit stones, say 2000 or above, you won't feel this). This may take up to 30 or 40 strokes, and is the indication that you should switch and start sharpening the other side.
Step 8: Start Sharpening Second Side
To sharpen second side, place the heel of the blade near the base of the stone, again maintaining a 15 to 20 degree angle. Gently push the blade away from you while simultaneously dragging across the stone towards the tip.
Step 9: Finish Second Side
Your stroke should end with the tip of the blade against the top edge of the stone, still maintaining a 15 to 20 degree angle. Remember to moisten your stone between strokes if it begins to dry out. Repeat for as many strokes as it took you to form the burr on the first side.
Step 10: Fix Stone
After repeated use, your stone will begin to develop grooves in it, which can hinder its sharpening power. To fix it, use a low-grit stone fixer. Place the fixer flat against the stone, and push it back and forth to grind down the stone and create a new, flat surface.
Step 11: Clean Up
You should have a dedicated towel for this purpose, as the grit from the stone will never come out. After carefully drying the stone (allow it to dry on a rack for at least a day), I store my stones wrapped directly in their towels.
Step 12: Hone and Test Your Blade
After sharpening, hone your blade on a honing steel in order to get the edge in alignment, then test it for sharpness. Some people recommend trying to slice a piece of paper in half by holding it up and slicing through it. I find that even a relatively dull knife will pass that test, yet fail at other kitchen tasks.
The best test is to simply use the knife to prep a vegetable. Do you notice any resistance? Does it fly through that onion? Can you slice a ripe tomato thin enough to read through it? Yes? Then you're done!
About the author: J. Kenji Lopez-Alt is the Chief Creative Officer of Serious Eats where he likes to explore the science of home cooking in his weekly column The Food Lab. You can follow him at @thefoodlab on Twitter, or at The Food Lab on Facebook.