How to Sharpen a Knife
Sharpen a kitchen knife on a whetstone. Test the edge, secure the wet stone, hold one angle, raise a burr on both sides, finish on the fine grit, and hone between sharpenings.
You will end up with a kitchen knife that passes the paper test again, sharpened on a whetstone at one steady angle, and a honing routine that keeps the edge between sharpenings.
Sharpness is a safety matter as much as a cooking one. N.C. Cooperative Extension explains that a dull knife is more dangerous than a sharp one, because it takes more force to cut, which makes it more likely to slip in the wrong direction and cut you.
The steps use a whetstone, which lets you set the angle your knife's maker specifies. Step 1 separates sharpening from honing, a different job done with a different tool, and step 2 tests whether the knife needs sharpening at all. These steps are for a straight edge, so if your knife is serrated, read FAQ 3 below first.
A whetstone (also called a sharpening stone) with two grits, a medium side around 1000 grit and a finer side of 3000 to 6000 grit for finishing. Zwilling's knife guide gives 800 or 1000 grit as the grain for a blade that has dulled only slightly, followed by a finer grain to finish. Keep the instructions that came with the stone, because step 3 depends on them. You also need a damp towel or a non-slip base to go under the stone, a bowl of water, and a sheet of printer paper for testing. A honing steel maintains the edge between sharpenings (step 7).
Understand sharpening versus honing
Sharpening and honing are two different jobs. Sharpening removes metal from the blade to put a fresh edge on it. You do it on a whetstone when the knife fails the test in step 2. Honing does not grind a new edge. It realigns an edge that has bent out of line with use, and you do it regularly with a honing steel, the long rod that comes with knife sets. Those are the definitions in Shun's care guide, which adds that regular honing cuts down on the need for sharpening and extends the life of the knife. Honing is like combing messy hair back into place. Sharpening is like getting a haircut. Hone first. When the knife is dull and honing no longer improves it, sharpen.
Test your knife before sharpening
Test on paper or food, never on your thumb or a fingertip. Hold a sheet of printer paper in the air by its top edge, with your fingers out of the blade's path, and draw the knife down through it. Zwilling's version of the test is that a sharp blade glides through the sheet without serious pressure. A dull one tears the paper or catches. You can also slice a ripe tomato without pressing down. A sharp knife bites into the skin under its own weight and the slicing motion, and a dull one slides across the surface. If the knife fails, hone it first (step 7 shows how) and test again. If it still fails, it needs sharpening.
Wet and secure your whetstone
Read the instructions that came with your stone before you wet it, because the rules differ by type and the wrong one can damage the stone. A soaking stone goes under water first. Zwilling says to immerse its stones for about 5 minutes. A splash-and-go stone does not. Shapton says its stones need no soaking after a first-use soak of 5 to 6 minutes, only a splash of water on the surface, and that soaking them for more than 30 minutes can soften them. A combination stone can need both treatments. The retailer Korin's instructions for the King 1000/6000 stone are to soak only the 1000 side, for roughly 2 minutes, and to splash the 6000 side. Korin warns that soaking a finishing stone of 3000 grit or above can crack it. Diamond plates need no soaking, and DMT says to use its diamond sharpeners dry or with water only. Secure the stone before a blade touches it. Set it on a damp towel or in its non-slip base, on a flat counter, with the coarse side (the lower grit number) facing up, and push on it to check that it cannot slide. Keep the surface wet while you work. Zwilling notes that the gray liquid that forms during sharpening is normal and improves the result.
Find and maintain the correct angle
Sharpen at the angle your knife's maker publishes, measured per side between the blade and the stone. A common rule gives Western knives 20 degrees and Japanese knives 15. The figures makers publish do not follow it. Wusthof publishes 14 degrees per side for its standard blades and 10 for its Asian-style ones. Zwilling tells owners to hold its knives at approximately 15 degrees on a honing steel, and Shun sharpens its knives to 16 degrees on each side. If you cannot find a figure for your knife, use 15 degrees, which sits inside the range those three makers give for standard blades. To set the angle, measure your blade from spine to edge and lift the spine to about a quarter of that height above the stone. That gives about 15 degrees on any knife, because the angle depends on the ratio of the two. A fixed prop under the spine, such as a stack of coins, does not work the same way on every knife. A 3 mm stack gives about 15 degrees under a narrow 12 mm blade, about 7 degrees under a 25 mm blade, and about 4 degrees under the 45 mm heel of a chef's knife.
Good to know: A steady angle matters more than an exact one. The sharpener maker DMT says sharpening at the proper angle is not as important as sharpening at a constant angle, and its advice for holding one is to lock your wrist.
Sharpen the first side on the coarse stone
Keep your fingers off the cutting edge for the whole of this step. Zwilling's instruction is to place your free hand on the blade but never directly on the cutting edge, because touching it can cause serious injury. Hold the handle in your dominant hand and lay the blade on the stone at your chosen angle, with the edge facing away from you. Rest the fingertips of your other hand on the flat of the blade, behind the edge. With moderate pressure, push the knife forward across the stone in a sweeping motion from heel to tip, as if you were shaving a thin layer off the top of the stone. Lift the knife, return to the start, and repeat. Work in sections from the heel of the blade to the tip, 5 to 10 strokes per section, until you have covered the whole edge. The sign to look for is a burr on the opposite side of the edge, which Zwilling describes as a line of waste metal that becomes visible after 5 or so strokes. A burr along the full length of the blade means this side is done.
Sharpen the other side
Flip the knife over and repeat on the other side, with the same number of strokes and the same pressure, so the edge stays centered. Then check for the burr. Never run a finger along the edge. Slide your thumb lightly across it instead, from the spine toward the edge and off. When you have raised a burr from each side in turn, the coarse sharpening is done. Turn the stone to the fine side, wet it the way its maker says (step 3), and repeat on both sides with lighter pressure, about 5 strokes per section. The fine side removes the burr and the leftover steel.
Test the edge and hone for maintenance
Wash the knife by hand and dry it before it goes near food. Wusthof says to always hand wash a knife after honing or sharpening, to remove the excess steel from the blade. Then repeat the paper test from step 2. If the knife still tears the paper, do another round on the fine side, 5 strokes per section on each side, and test again. From here on, keep the edge with a honing steel. Stand the steel point down with its tip on a non-slip surface such as a cutting board. Hold the knife against it at the same angle you sharpened at, and draw the blade down the steel from heel to tip, pulling it toward you as it goes. Repeat on the other side of the steel. Wusthof's count is 6 to 8 times, alternating sides. Hone regularly. Shun suggests about once a week for its knives, depending on use.
If the knife still fails the paper test after the fine side, either the angle wandered or the coarse side never raised a burr along the whole edge. Go back to the coarse side, hold the quarter-height angle from step 4 with your wrist locked, and work each section until you feel the burr from heel to tip. If only the tip or the heel is dull, those sections got too few strokes, so give them their own passes. To protect the new edge, wash the knife by hand and store it where the blade touches nothing else, in a knife block, on a magnetic strip, or in a blade cover. That is the care advice N.C. Cooperative Extension gives. Then put the knife to work. Our guide on how to meal prep lists a sharp knife among its tools.
Questions we get asked about this
Answers from experience, not a textbook.
Sharpen when the knife fails the paper test in step 2 and honing no longer fixes it. No fixed interval fits every knife, and the sources we read give different ones. N.C. Cooperative Extension says kitchen knives should be sharpened at least once a year, and preferably more often. Shun warns that sharpening is not something to do every week, because it removes metal and doing it too often can shorten the knife's life. Between sharpenings, hone as in step 7.
An uneven edge from a wobbling angle is fixable. Sharpen again at one steady angle and it evens out. What you cannot put back is metal. Every sharpening removes some (FAQ 1 above), and Wusthof warns that pressing down in a pull-through sharpener can remove excess steel and compromise the edge. On a whetstone, use moderate pressure on the coarse side and lighter pressure on the fine side, and stop when the knife passes the paper test.
No. The steps above are for a straight edge. Zwilling says never to hone a serrated knife, and that serrated knives must be sharpened by a professional or replaced. Take a serrated bread knife to a sharpening service, or ask its maker whether it runs one.
Buy one only if its preset angle matches your knife. Wusthof lists hand-held and electric sharpeners among the tools its knives can be sharpened with, and says both kinds have preset angles that guide the knife. That preset is the limit. Shun tells owners who choose another brand's electric sharpener to make sure it sharpens to the correct angle, which for Shun is 16 degrees. Check the sharpener's stated angle against your knife maker's figure (step 4) before you buy. A whetstone takes practice and works at any angle, which is why the steps above use one.
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