Knife Sharpener Myths & Facts
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Every year, thousands of knives are given as gifts for many special occasions — weddings, birthdays, Christmas, Hanukkah, graduations — with no reports of negative consequences. For those who want to err on the safe side: a penny can be taped to the gift-wrapping and the recipient can “pay” the donor for the gift.
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Those who subscribe to this view can pick up the fallen flatware, wash it and set the table to entertain their unexpected guests! Nonbelievers should take note: never try to catch a falling [sharp] knife.
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A sharp knife is safer than a dull knife. A dull knife can slip off food and cut the user. The excessive force needed to make a dull knife cut causes the user to lose control, i.e. the knife can ‘break out’ of the material being cut and cause injury. A sharp knife requires little force, so it’s easier to control and cuts where intended. The user is more likely to treat a sharp knife carefully.
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The edge of a quality knife does not wear away; it folds over on itself. A knife-edge is microscopically thin — much thinner than a human hair. The impact of cutting causes the edge to fold over on itself. Pieces of the edge may even break off.
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Unless the professional knife sharpening service is using a sharpener that will not overheat (detemper) knives and will not remove too much metal, it’s better to sharpen your knives at home using widely available professional diamond abrasive home knife sharpeners which are safe for quality knives. Many professional knife sharpening services use conventional grinding stones that remove too much metal and detemper (overheat) the knife-edge. If a sharpener creates sparks it is detempering the knife. The person doing the sharpening may not be properly trained. It may take several days or weeks to get knives back. Today, professional quality home knife sharpeners reliably create a razor-sharp edge every time they are used. These sharpeners provide built-in precision angle guides to eliminate guesswork and 100-percent diamond abrasives that will not detemper fine knives.
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The traditional sharpening steel does not sharpen; it maintains the edge by unfolding it. This straightened edge is still weak and quickly folds again. Eventually, the edge breaks off or folds so tightly that it can’t be straightened with a steel and must be reshaped. Using a steel requires significant skill and practice. To be effective at all, the steel must be used after every 10 to 50 cuts, before the edge folds over too much to straighten. True sharpening removes the old weak edge and reshapes a new stronger edge.
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The steel alloys used to make knives are crystalline in structure, not molecular, so there are no molecules to realign. Magnets will not resharpen a knife. They have no effect on the steel alloy or the durability of the edge.
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Unless the user is highly skilled, the edge created on a conventional sharpening stone will not be as sharp or as strong as an edge created by a professional home sharpener with built-in angle guides. To stay sharp longer, a knife-edge must be perfectly symmetrical. If it leans to one side it will fold more quickly. Traditional stones provide no angle guides to help create a symmetrical edge. They are time consuming and require skill and effort.
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Makeshift sharpening methods can damage good knives and won’t create sharp, durable edges. Rough stone or ceramic surfaces can produce a ragged, uneven edge. Like a sharpening stone, these methods do not incorporate precision angle guides. In addition, their surfaces are ragged and uneven. It is very difficult to create a uniformly sharp, symmetrical edge this way. Worse, both of these methods can rip off metal, shortening the life of the knife.
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A “V”-shaped or hollow-ground edge gets dull faster than an arch-shaped edge. The edge of a quality knife does not wear away; it gets dull because it folds over on itself. The secret to keeping knives sharp longer is to create an edge that resists folding. An arch-shaped edge has more metal supporting the cutting edge and will stay sharp two- to three-times longer than a “V”-shaped or hollow-ground edge.
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Sharpeners with a “V”-shaped slot – – such as crock sticks, one-stage electric sharpeners and sharpeners with overlapping washers – – do not provide precision angle control and cannot reliably produce a sharp, symmetrical edge. If the knife “wobbles” from side to side while it is pulled through the slot, the edge will not be symmetrical. Only sharpeners with precision guides that keep the knife at the exact same angle along the entire length of the blade, create symmetrical edges. Metal washer-type sharpeners can rip the knife-edge and remove excess metal.
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Recently developed professional-quality manual knife sharpeners are extremely effective, safe and easy to use. Look for sharpeners with built-in precision angle guides and 100-percent diamond abrasives. Diamonds will not detemper knives and precision guides make shaping the edge foolproof.
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Years ago, this was true. However, a new class of electric knife sharpeners is safe for quality knives. Most single stage electric knife sharpeners (especially “free” sharpeners built into the back of electric can openers) damage knives. They use harsh abrasives which throw sparks (indicating the edge is overheated), remove too much metal and can gouge knives. These sharpeners provide no angle control and cannot produce a strong, symmetrical edge. The new class of safe sharpeners uses 100-percent diamond abrasives and built-in precision sharpening angle guides, safely creating a stronger arch-shaped edge that resists dulling two- to three-times longer than conventionally sharpened edges.
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Sparks produced during sharpening mean the knife is being damaged. The sparks are actually bits of red-hot, overheated metal coming off the knife. They indicate that the grinding wheel is seriously overheating the knife-edge, which detempers (weakens) it.
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Most original edges, as delivered from the factory, are a weak “V”-shape and actually become much stronger when resharpened to a longer-lasting arch shape. Factory edges vary widely in quality; even those produced by well-known European cutlery companies. It is better NOT to restore the “original” edge but to create a new longer-lasting arch-shaped edge.
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Never-need-sharpening knives are serrated, like a saw blade. A serrated knife does get dull because the teeth become bent and misaligned. A serrated knife functions like a saw, which will continue to cut, after a fashion, even when relatively dull. However, when dull, it will shred or tear rather than slice cleanly. There are several types of “never-need-sharpening” knives. Most serrated edges are created by mechanically grinding or laser-cutting the blade. Today there are sharpeners that quickly and easily revitalize serrated edges restoring their ability to cut smoothly. However, some “never-need-sharpening” knives have blades sprayed with a hard metallic coating such as tungsten carbide. A tungsten carbide edge is very brittle and in a relatively short time (less than a few months in most home kitchens) pieces break off and the edge becomes jagged, cutting in somewhat the same fashion as a serrated edge. These blades cannot be satisfactorily sharpened by home sharpeners and must be returned to the factory for refurbishing.
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Sharpening and realigning the prominent teeth will resharpen a serrated knife. It is not necessary to sharpen the scallops between the teeth. Like a saw, the tips of the teeth do most of the cutting.
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There are electric and manual knife sharpeners that safely sharpen serrated and “never-need-sharpening” knives (which are also serrated and do need resharpening). These sharpeners use built-in precision angle guides and 100-percent diamond abrasives to realign serrated knife teeth and to sharpen each tooth so it is shaped like a tiny knife or “micro-blade.”
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The type of cutting board used has a much greater impact on knife-edge durability than the food it cuts. Many hard cutting boards (made of acrylic, glass, granite, marble, synthetic stone) cause knives to dull much faster. Polyethylene or polypropylene boards are best for knife-edges and, in addition, they can be sanitized in the dishwasher or bleached in the sink. Wood boards are second best in terms of knife-edge maintenance.
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Washing sharp knives in the dishwasher can be hazardous to the knife, the dishwasher and the cook! It is too easy to reach into a dishwasher and get a nasty cut. Sharp knives can knick plastic-coated wire shelves and other utensils. The force of the water can dull knife-edges by pushing them against shelves or utensils. The combination of hot water and the chemicals in dishwasher detergent can leave stains on stainless steel cutlery that comes in contact with silver or silver-plated flatware or copper. (These stains don’t effect the knife’s performance.)
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Knives should be stored in a knife block, knife drawer insert or secure magnetic rack. Loose in a drawer, knives can cut the unwary hand or nick other utensils or the drawer itself. Magnetic knife racks can be effective as long as the knives are held securely and the rack is not located where the exposed knife-edges could cause injury.
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There are major differences among the alloys used in kitchen knives. The best alloy guarantees an edge that stays sharp longer, which means the knife cuts better, needs less sharpening and lasts longer. Early knives were made from refined iron ore that was “cast” or molded. Cast iron is strong, hard and takes a good edge but it oxidizes (rusts) easily and can be too brittle or too soft. Steel, a combination of refined iron ore with other elements, is harder than cast iron but still quite brittle and it, too, rusts easily. Carbon steel is a stronger alloy but is still prone to rusting and brittleness. Stainless steel is a mixture of iron, carbon and various additional elements, especially chromium, which give the alloy high rust-resistance and reduced brittleness or improved ductility (resilience). It’s important to note that the performance properties of stainless steel depend to a large degree on how the alloy is processed — whether it is stamped or forged — and how well it is manufactured.
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Hardness is a factor in edge durability, but it must be balanced with resilience or the knife will be too brittle and the edge will “chip out” and become dull. A strong, tough alloy is ductile (resilient). A strong blade will actually ring like a bell when tapped on a hard surface. Like a bell, which must withstand multiple blows from its clapper, a knife must be resilient enough to repeatedly withstand the impact of hard foods and cutting surfaces.
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Most stainless steel knives are softer than carbon steel knives and are as easy or easier to sharpen, but do not stay sharp as long. Carbon steel is harder than most stainless alloys but it can also be brittle, so pieces of the knife-edge can break off. Carbon steel edges are weakened by the alloy’s tendency to rust easily.
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To increase stain resistance, early stainless steel alloys contained an excessive amount of chromium, which made the alloy too soft to form a durable edge. Later alloys increased edge durability. Today, a new ultra-high carbon alloy gives knives exceptional edge retention. Today’s stainless alloy knives take a durable, razor-sharp edge because they contain a much lower percentage of chromium while still retaining excellent stain resistance. A recently introduced forged knife line made from a unique ultra-high carbon stainless alloy holds an edge up to ten times longer than any other stainless kitchen knife and has excellent stain resistance. The new alloy contains about 1% carbon (for hardness), twice the carbon of any other forged kitchen knife. Unlike carbon steel knives that tend to be brittle, this new alloy is resilient, due in part to the fact that it contains between 10 and 30 times the molybdenum (for ductility or resilience) of any other forged kitchen knife. This alloy is as strong as carbon steel and takes an edge that is as sharp or sharper.
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None of the metal alloys used in knives are truly “stain-free” or “stainless.” Most are stain-resistant. Stainless steel knives should never be soaked for lengthy periods or put in high-concentration bleach solutions or salt water. Primarily for safety reasons, stainless steel knives should not be washed in the dishwasher. A stainless knife placed in contact with a metal pan or utensil can pick up a stain due to the chemical reaction of the two metal items in combination with hot water and dishwasher detergent. Such stains do not affect performance.
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Stamped knives are cut, cookie-cutter style, from sheets of rolled steel. They are not as strong and do not hold an edge as well as forged knives. Forging strengthens steel, creating a fine, homogenous grain structure with more ductility (flexibility) in much the same way as kneading yeast bread produces a finer crumb and more resilient texture than the more brittle texture of baking powder biscuits cut from sheets of rolled dough.
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A one-piece knife, forged from a single bar of alloy, is the strongest knife structure. Weld points are weak by comparison. Some manufacturers cut costs by welding together stamped knife parts with forged knife parts creating “imitation” forged knives that are not as strong as knives forged entirely from a single bar of alloy.
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A thick bolster is a safety feature on most types of knives but can reduce the useful life of a chef’s knife. Thick bolsters help keep the hand from slipping onto the blade, especially when the blade is used close to the hand. (As with a boning or paring knife.) However the best bolster for a chef’s knife is tapered so that it is no thicker at the heel than the rest of the blade. This allows the entire edge of the chef’s knife to be sharpened for the life of the knife. Old-fashioned chef’s knives with thick bolsters eventually prevent sharpening of the entire edge. An indentation or “swale” develops near the bolster and part of the edge no longer contacts the cutting board, making the knife virtually useless.
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The tang should extend the full-length of the handle. This gives additional strength to the handle. A partial-tang handle is more prone to cracking and breaking. A full-length tang also allows the knife to be balanced properly so the center of gravity is over the working fingers.
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A handle molded around a full-length tang is much stronger than a riveted handle or a pre-molded handle shoved onto the tang. Riveted handles have crevices, can crack (as can pre-molded handles) and can harbor bacteria. A molded-on handle will never come off and seals out bacterial cross-contamination.
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Significant differences among knife handles make them an important consideration when selecting kitchen knives. Since a knife is an extension of the hand, a knife handle should be safe, comfortable and designed to help prevent fatigue and repetitive motion injuries. It should be shaped so that the grip is comfortable and secure (wet or dry) and the orientation of the blade to the food is optimal. The best handles have a textured surface to prevent the knife from slipping out of the hand. Extra-long or oddly shaped handles can interfere with a smooth cutting motion and irritate the hand. There should be plenty of knuckle clearance beneath the handle of a chef’s knife — even the shorter chef’s knives — so the knuckles aren’t bruised when chopping on a cutting board.