What the best knife sharpeners have
- Good performance. A sharpener's most important feature is its ability to produce a consistently keen, smooth edge without any nicks or scratches in it.
- A hard, abrasive surface. Generally speaking, diamond is the hardest (and thus fastest) sharpening material, followed by tungsten carbide and polished ceramic. Abrasiveness is measured in terms of grit; the higher the grit number, the finer the abrasive. So 120-grit material is extremely coarse, while 1000-grit is quite fine.
- An accurate, adjustable angle guide. Some sharpeners make it easy for even an inexperienced user to hold the blade at the correct angle, while others require a bit of practice. The best angle guides adjust to accommodate multiple blade angles, especially 15 and 20 degrees, which are the two most common blade angles for kitchen cutlery.
- Multiple sharpening stages. A coarse abrasive is used to reshape the edges on truly dull or damaged knives, while finer abrasives serve for touch-ups and polishing. Having both is essential because if you use coarse material for small touch-ups, you'll remove too much steel from your knife.
- Adequate safety features. It should be easy to use the sharpener without taking off bits of your fingers in the process. Manual sharpeners accomplish this by putting a physical barrier between your fingers and the knife blade. Electric sharpeners use slots or rails to guide the knife into the sharpening disks or belt, instead of your hand.
- A decent warranty, backed by good customer service. This is more important for electric sharpeners, which tend to cost $100 or more.
Know before you go
What kind of knives do you have? Every sharpener can handle straight-edged blades, but only a few can sharpen serrated (scalloped-edge) knives. However, these knives degrade more slowly than straight-edge ones, so you may not need this feature if your serrated knife doesn't see heavy use. Also, not every sharpener can sharpen sport knives, scissors or Asian-style knives with a narrower edge than a standard kitchen knife. If you want to sharpen these types of blades, look for a sharpener that's designed to handle them.
How patient are you? Electric sharpeners generally get the job done faster than manual ones. They also tend to be easy to use, while some manual sharpeners take a little time to master. For instance, some reviewers rave that water stones deliver beautifully polished edges, but using them takes a steady hand and plenty of practice.
How much space can you spare? Most manual sharpeners are small enough to fit in a kitchen drawer. Electric sharpeners, by contrast, take up space on your kitchen counter or in your cabinets. They're usually about as long as a toaster and somewhat lower in profile.
What's your budget? Manual sharpeners tend to be cheaper than electric sharpeners. Manual sharpeners also cost less to run and, because they don't have any moving parts to go wrong, tend to last longer.
Does noise bother you? Some electric sharpeners can be noisy. On the other hand, the whir of the motor masks the scraping sounds of the blade against the stone. Some people find that scraping sound -- which is front and center for manual sharpeners -- to be more annoying.
Are you left-handed? Most manual sharpeners can be used either right- or left-handed, as can most countertop electric sharpeners. One belt sharpener we evaluated, however, is made for right-handers only.
How much do you value your knives? Many electric sharpeners, and some manual ones, can over-grind knives and reduce the life of the blade. Warping and chipping can also be a problem. If you have expensive knives that you want to protect, look for a sharpener that doesn't generate a lot of heat and is gentle on the metal.