Knife Sharpeners

Published July 1, 2015. From Cook's Illustrated.

Overview:

Japanese bladesmiths have long favored chef’s-style knives with blades that are ultraslim—that is, sharpened to about 15 degrees on either side of the blade—and for good reason: In addition to being thin and lightweight, these blades have a supernarrow cutting edge, which helps make them razor-sharp. We’ve also come to favor a thinner edge. After years of testing dozens of knives, our repeat favorite is from Victorinox, a Swiss-made knife that is sharpened to 15 degrees on either side of the edge, allowing it to push and slide through food more easily than do more traditional European blades sharpened to at least 20 degrees.

To maintain that narrow edge, we use a tool specifically designed to sharpen a blade to 15 degrees. Our favorite models, both from Chef’sChoice, are a manual and an electric sharpener that each do a fine job of restoring an ultrakeen edge to an Asian-style knife. But in recent years the trend toward slimmer knives—and slimmer knife sharpeners—has spread west, as European manufacturers including Wüsthof,… read more

Japanese bladesmiths have long favored chef’s-style knives with blades that are ultraslim—that is, sharpened to about 15 degrees on either side of the blade—and for good reason: In addition to being thin and lightweight, these blades have a supernarrow cutting edge, which helps make them razor-sharp. We’ve also come to favor a thinner edge. After years of testing dozens of knives, our repeat favorite is from Victorinox, a Swiss-made knife that is sharpened to 15 degrees on either side of the edge, allowing it to push and slide through food more easily than do more traditional European blades sharpened to at least 20 degrees.

To maintain that narrow edge, we use a tool specifically designed to sharpen a blade to 15 degrees. Our favorite models, both from Chef’sChoice, are a manual and an electric sharpener that each do a fine job of restoring an ultrakeen edge to an Asian-style knife. But in recent years the trend toward slimmer knives—and slimmer knife sharpeners—has spread west, as European manufacturers including Wüsthof, Henckels, Messermeister, and Mercer have launched their own 15-degree knives and sharpeners. (In fact, Wüsthof and Henckels have discontinued their 20-degree knives.) We were curious to see what these new sharpeners had to offer—and were especially eager to test the claim of one that it can even hone a 20-degree knife to 15 degrees. How would the best knife sharpeners perform?

So we rounded up nine models (including our previous favorites), five manual and four electric, from both Western and Asian manufacturers and priced from roughly $20 to $200. To evaluate them, we bought nine of our favorite Victorinox chef’s knives and assigned one to each sharpener; we then dulled the knives identically and sharpened them according to manufacturer instructions. To assess sharpness, we slashed sheets of copy paper and sliced delicate tomatoes, repeating the dulling, sharpening, and slicing process four more times with multiple testers (for more information, see “Testing Knife Sharpness” in related content).

Material World

All knife sharpeners work similarly: The user repeatedly drags the blade against an abrasive surface at a set angle, which trims and reshapes the blade by removing microscopic amounts of metal that are blunted or too far out of alignment. (Honing a blade on a steel is for knives that are less dull, as it simply repositions metal that is only slightly out of alignment.) With electric sharpeners, the abrasives are on motorized wheels that spin against the blade; with manual sharpeners, they’re either on nonmotorized wheels or the abrasive material itself is fashioned into a V-shaped chamber through which the user pulls the knife.

Despite sharing similar mechanisms, the sharpeners we tested produced dramatically varied results. There were differences in user-friendliness: Some came with unintuitive directions and designs or fussy cleaning requirements; others made jarring vibrations or piercing grinding noises. We docked points for all these flaws.

But what really divided the pack was how sharp—or not—the knives were after we sharpened them. Some models barely restored the knife’s edge and others actually damaged it, rendering it uneven or jagged so that the knife struggled when it came in contact with the food. And then there were the best sharpeners, which put such a keen edge on the blade that it felt sharper than it did out of the box.

We first checked to see if electric and manual sharpeners performed comparably—and for routine sharpening, they did. (Repairing deep nicks was another story; more on that later.) It wasn’t until we examined the inner workings of the sharpeners that we realized that two key factors were determining how effectively they sharpened.

First, the type of abrasive. The models we tested used three different kinds: carbides (a combination of metal and carbon), ceramic, and diamond. Our least favorite models featured carbides or ceramic, materials that proved problematic in part because they have what Mike Tarkanian at the Massachusetts Institute of Technology’s Department of Materials Science and Engineering calls a “high coefficiency of friction.” This means that they are relatively sticky and grab at the surface of the blade more than diamond does. As a result, sharpeners made of these materials rough up the surface of the blade, making it move through food less efficiently. In addition, ceramic and carbides are also softer than diamonds and degrade more quickly, shortening the life span of the sharpener; in fact, the ceramic wheels on the electric Shun sharpener sent up a puff of white dust every time we pulled the blade through its chamber.

Diamond, on the other hand, is the hardest material in the world, which makes it strong and durable for sharpening. Its coefficiency of friction is also relatively low, which allows it to glide smoothly over a knife blade as it sharpens and thus produce a smoother, sharper edge.

In Chambers

The second factor affecting sharpness was the design of the sharpening chamber. For the abrasive to put a consistently smooth edge on the entire blade, the blade must move through the chamber as steadily as possible; if there’s any wiggle room, the blade can shift position slightly from stroke to stroke and emerge unevenly sharpened. The Wüsthof, Victorinox, and Kuhn Rikon sharpeners, for example, all had poor blade support, so testers naturally eased up on pressure when the blades were almost through their chambers, lest they push the blades off the sharpeners and onto the counter. As a result, the knives assigned to these sharpeners had noticeably duller tips that couldn’t cut through paper and squashed tomatoes flat. Examining the blades under a high-powered microscope at MIT confirmed that they were utterly ragged from all that wobbling.

The best designs came from a single manufacturer. Both of its electric models feature spring-loaded guides in their chambers that supported the entire edge, allowing for smooth, consistent contact with the abrasive; on its manual model, the company built high sides that held the blade at a precise, secure angle so that testers could draw it through the chamber with even pressure.

Power Hungry?

With diamond abrasives, supportive chambers, and intuitive design, all three models from one maker (two electric and one manual) put razor-sharp edges on very dull knives and were easy to use. But whether you buy a manual or electric model depends on your needs and personal preferences. Manual sharpeners are smaller, lighter, cheaper—our repeat top-rated manual sharpener costs about $50—and easier to store. They also don’t need to be unpacked and plugged in for use, making them a more convenient option for routine upkeep.

But what even the best manual sharpener can’t do is repair extensive damage to a blade. When we filed two identical notches into the ends of each knife and then ran them through their respective sharpeners, the winning manual model hadn’t made much progress after 300 strokes. But since the electric models put the abrasive in contact with the blade at a much higher speed, they quickly repaired the damage, giving them a distinct advantage over manual models. Our winning electric model, the only model to feature a dedicated slot for heavy damage, required only 76 strokes to make a severely damaged knife look and cut like a brand-new blade. Meanwhile, the runner-up electric model, got the job done in about 220 strokes.

While our winner does have a hefty price tag, its heavy damage slot offers another compelling reason to buy it, even if you don’t own a 15-degree knife: As advertised, it can indeed narrow the angle of a traditional Western blade, converting it from 20 degrees to 15 (see “Angling for a Sharper Edge”). With this ability, it may just be the last sharpener you’ll ever need to buy.

Angling for a Sharper Edge

The manufacturers advertise that the aggressive first slot on the Chef’sChoice Trizor XV can narrow the angle of a 20-degree Western blade to 15 degrees—a function that would make this pricey model worth considering even if you don’t own a 15-degree knife.

We tested that claim by running a brand-new 20-degree chef’s knife through the Trizor for 20 strokes on either side of the blade (per manufacturer’s directions). We then compared its sharpness to a second new copy of that knife, as well as a new copy of our favorite 15-degree chef ’s knife from Victorinox, by having multiple testers slice through crates of produce. The results were convincing: Testers reported that the copy with the narrowed edge felt noticeably sharper than its sibling and almost as sharp as the 15-degree Victorinox.

Degrees of Sharpness

When manufacturers report that a knife has a 15- or 20-degree angle, they’re referring to the angle of the bevel—the slim strip on either side of the blade that narrows to form the cutting edge. The more acute that angle, the sharper the blade will feel.

Methodology:

We tested nine knife sharpeners, four electric and five manual. Models are listed in order of preference. All were purchased online.

  • ROUTINE SHARPENING: We bought new copies of our winning chef’s knife, the Victorinox 8" Swiss Army Fibrox, and assigned one to each sharpener. We dulled them identically and sharpened each according to manufacturer instructions. To rate their sharpness, we slashed sheets of paper and sliced tomatoes and then repeated the dulling, sharpening, and slicing process four more times with different testers. Those that made clean cuts without crumpling the paper or damaging the fruit rated highest.
  • NOTCH REMOVAL: We filed notches in both ends of each blade and ran them through their respective electric sharpeners (manual models could not remove notches), timing how long—and counting the number of strokes—it took to repair the damage.
  • DESIGN: Sharpeners that had clear, precise instructions, were intuitive to use, and cleaned up easily rated highest.
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