Knives are among the most essential kitchen tools for any housewives. A keeping knives sharpened so they will work properly is a major concern of everyone who has to work with them. No matter whether a knife is made of carbon steel, high carbon stainless steel of conventional low carbon stainless, it will lose its edge after slicing meat and vegetables.
There are a number of ways to sharpen a knife. Over the past decade or so, several new methods have come into use, but they exist side by side with techniques which have been around for centuries.
The day of the pickup and delivery by the local knife sharpener has disappeared for many of today’s foodservice operators. Most of those specialists still in business are located in larger cities or in smaller communities where the knife sharpener makes a living sharpening chain, circular and hand saw, barber’s shears, lawn mowers, etc. Too often operators and their kitchen personnel must see to the sharpening themselves. Chefs trained in the European tradition generally prefer to do their own sharpening.
Types of Knife Sharpeners
Today the average kitchen has one, and usually two or more different types of knife sharpeners. To old timers there is a difference between “sharpening” and “honing” a knife. To them, honing means running the cutting edge of a knife against a smooth or lightly abrasive surface, usually a round “steel.” This is shaped like a short, round rod, with a handle and sometimes a crossbar guard to protect the hand.
Some European-trained chefs still use a leather hone, a smooth piece of leather mounted on a block or in strap from (often referred to as a “strop”). Leather is slightly abrasive and thus hones the edge of the blade when it is drawn accross the material.
There are also mechanical honers, usually very fine abrasive wheels or discs which provide more of a polishing action than grinding. Most honing in a foodservice operation, however, will be with a steel sometimes with a leather hone or strop. After sharpening, a hone is often used to remove the “feather” edge formed by sharpening. During knife use, honing is used to “burnish” the edge of a knife by removing the “burrs”–rough spots which occur as a blade is used. But honing does not really sharpen a dull blade.
Because of the convenient shap, manual sharpeners have been developed using the “steel” format. These do more than just jone; they sharpen blades through either abrasive or actual cutting action.
Originally steels were smooth or they were scored lengthwise or knurled with grooves. The material of these steels, however, was about the same hardness or only slightly harder than the metal used in the knife blade (until a few years ago almost all professional knife blades were made of high carbon steel). Therefore, removing the feather and deburring the cutting edge was about all steel could do. Both of these types of steels are still used by cooks and chefs to keep their knife blades in condition between sharpenings. While the majority of steels have a round cross-section, there are a number of cooks who prefer an oval shape to the rod, and several manufacturers provide such configurations.
Most steels are magnetized to prevent metal dust or chips from scattering as they are formed by the mild abrasive action. A damp cloth or washing removes the debris. With improvements in metals technology, a number of materials have been developed which are harder than the knife blade. One of these is high carbon chrome vanadium tool steel. Another is the same kind of steel used in file blades. These two metals scored or knurled work like fine files on the blade of a knife being sharpened. They actually cut away metal to form a sharp edge. Such steels usually are magnetized.
Also available in the same rod shape as a steel and sometimes referred to as “sticks” are some of the new abrasive materials which have been developed in the past few years. One is aluminum oxide ceramic, a “space age” material. Another has a surface of zirconium, and there is even a sharpener covered with diamond crystals. These materials all sharpen, that is, they remove metal from the knife blade, generally in a grinding or cutting action.
- Steels and sticks are usually available from the major professional knife manufacturers. They are also available from specialized sharpener manufacturers, particularly those made of some of the more exotic materials, such as carbide and diamond.
- Another cutting material used in sharpening is carbide, the same hard metal which is used in drills used to cut into stone and concrete. Carbide is so much harder than the knife blade that drawing a blade across a sharp carbide edge will actually “shave” off minutes strips of steel.
A traditional tool for sharpening knives has always been the “stone,” the name derived from the fact that a form of sandstone was once used for that purpose. For the past century, however, stones have been formed of harder materials, both natural and manmade. These manufactured “stones” are made of uniformly sized particles (grits), which are bonded together into a block. Thus, various degrees of fineness or coarseness are available; often a fine and a coarse block bonded together back to back into one stone. In this way, the coarse side can be used to grind the blade rapidly, with the fine side used to form an even edge.
Many of the stones used to sharpen knives are oil stones, so called because oil is applied as a lubricant for the grinding. The oil acts as a deterrent to heating of the blade from the friction of grinding. Heat can remove the temper from the knife blade and thus interfere with its ability to hold an edge. Oil cannot be used on all stones, because it sometimes destroys the bond of stones which are not intended for that type of use. Oil stones are labeled for that use.
Here, again, even more effective cutting surfaces are available. One manufacturer produces a “stone” that is block covered with diamond crystals. Used like a regular stone, it doesn’t require oil since the cutting action is so quick that frictional heat is low. It may also be used as a file to shape the knife blade, particularly where the blade has been chipped or nicked badly.
The most common type of mechanical sharpener has a small round grindstone which is revolved at high speed by an electric motor. There is generally a guide surface against which the knife blade is placed, and that permits the blade to be drawn across the whirling stone at the proper angle. Because of the high speed at which the stone revolves and the light pressure that is recommended for sharpening, frictional heat is kept to a minimum and no cutting (cooling) liquid is needed. A variation on this type of sharpener uses a ridge stone to sharpen scallope (serrated) blades. Several ridge spacings are available to match the scallop pattern of different manufacturers. This type of sharpener also permits scalloping the edge of any knife blade or changing the scallops on a already scalloped blade. Some manufacturers offer either smooth stones or ridge ones for their sharpeners.
In addition to the standard wheel sharpener, there are available belt sharpeners that grind the knife against an abrasive coated belt which is electrically operated. Various grits from moderately coarse to very fine are available for this type of sharpener. Speed of the belt is usually similar to the speed at the surface of grinding wheel, so frictional heat is kept low.
Mechanical Hones on the Market
There are also several mechanical hones available for foodservice use. The basic difference between a hone and a sharpener is that the hone removes far less metal, and thus is more suitable for restoring the blade’s edge than to eradicate nicks and chips or change the angle of the cutting edge.
There are at least two types of hones available. One is the disc or plate hone, which consists of a whirling disc to which a past abrasive is applied. The other is a reciprocating hone (moves back and forth is a straight line) that uses a fine abrasive honing cylinder. Both of these electrical tools operate at high speed and use relatively fine abrasive, so there is little danger of losing temper through overheating the metal blade.
The reciprocating hone provides a small diameter cylinder which emits sharpening scalloped blades. You should know the various sharpening capabilities of the products you sell. For example, a smooth or knurled carbon steel hone will only burnish a blade between sharpenings. A steel one made of tool steel (chrome vanadium) or file steel will provide moderate sharpening, but will not change angles or easily remove nicks and chips.
- An abrasive stick, particularly one with a diamond surface, will provide more aggressive sharpening, but still not the equivalent of grinding. The same is true of most manual stones.
- A carbide sharpener will remove metal, but tends to follow the line of the blade and will not remove larger nicks or chips.
- A mechanical sharpener will remove metal quickly and enables the operator to change the angle of the blade edge or to remove nicks and chips with relatively little effort. Some mechanical grinders will perform hollow grinding, but many will not.
- A power hone will provide an excellent edge quickly, but will not remove nicks and chips easily. None of the standard sharpening or honing equipment or tools adequately sharpens so-called “offset” blades, used instead of scalloping by some knife makers.
Find out what the operator or kitchen help wants to do. Then suggest the proper tools for the job. Remember that most operators will have to send knives to a professional grinder about once a year unless they buy the same kind of professional equipment and learn to use it with the same skill the professional does. For many that is desirable; for others it is not.