As cooks are fond of pointing out, a dull kitchen knife is a dangerous one, and even the most expensive knives can lose sharpness over time. Fortunately, most dull cutlery can easily be brought back to life by sharpening. Although knives can be sent to a professional for this task, frequent users may find it more affordable to sharpen them at home with a manual or electric knife sharpener. These products use an abrasive on the blade, such as tungsten carbide, ceramic, steel or diamond (the hardest, most aggressive sharpening surface). Most have at least two sharpening areas; you start with a coarser grit, then use a finer grit to finish your knife edge.
Whether manual or electric, each type comes with its own set of trade-offs. Manual knife sharpeners are generally more compact and affordable. In fact, we found excellent reviews for one small manual sharpener costing less than $10. Fancier manual models, costing $50 or more, also offer users more control over the sharpening process, but these tend to require more skill. Electric knife sharpeners, on the other hand, don't provide much control, but they're faster and easier to use. They also tend to be larger -- about the size of a toaster -- and are designed to sit on your countertop. Expect to spend around $150 for the convenience.
The angle at which the knife is positioned during sharpening is key; most sharpeners offer various guides to help you keep your blade properly aligned. Manual rod systems, such as the Spyderco 204MF Tri-Angle Sharpmaker System (*Est. $55), fit ceramic rods into a base at preset angles to guide the sharpening process. Users pull the knife in strokes against one rod and then the other. These manual sharpeners do take a little time to master, however. Slotted sharpening systems are simpler; the user simply inserts the knife into a slot that holds it at the proper angle against the abrasive surface. Users then draw the knife through the slot to sharpen it.
While this style is very easy to use, it has limited control and often can be used only on straight blades. Electric sharpeners and some manual models employ this design. The trickiest sharpeners to use are flat whetstones, such as Japanese water stones. Although many experts like the control whetstones offer, they admit that it takes practice to master them, and we did not find any sharpeners of this type that received strong recommendations from home users.
To select our best-reviewed knife sharpeners, we considered four factors. The most important of these is performance, since there's no point in buying a sharpener that doesn't get your knives sharp. Nearly as important is ease of use, since even a top-performing sharpener won't do any good if you can't figure out how to use it properly. We also considered safety and noise level. To rate knife sharpeners on these criteria, we consulted professional comparison tests in publications such as Cook's Illustrated magazine and Choice, the Australian equivalent to Consumer Reports. We also looked at more casual tests in newspapers and on consumer websites. Finally, we consulted reviews at retail sites such as Amazon.com and Cooking.com to see how these sharpeners perform in the hands of typical home users.