1998 | No. 47
Revised April 2022
A Sharp Knife
Soft, Hard, Brittle, Tough, Resilient, and Wear-Resistant
The most important kitchen tool after a pot and a spoon is a sharp knife. A dull edge crushes and tears rather than slices. It doesn’t cut crisp vegetables so much as wedge them apart; it mashes tomatoes; it presses the juices from meat. Dullness requires more strength, and real force may cause a knife to slip dangerously. You can test the sharpness by pulling your thumb across the blade at a right angle to it and without pressure. A dull edge feels smooth, a sharp edge catches at your skin.
By Edward Behr
Most knives are stamped out of a rolled sheet of steel. The least expensive can be very thin (which isn’t automatically a defect); no one may have thought much about the shape; the cutting edge may be coarsely or incompletely ground; and the handle may not provide much to hold on to. But even the cheapest knife can be made fairly sharp.
The best knives are forged — hammered — from a single piece of hot steel. A forged knife has more dimension. It also costs much more than a stamped one. Some forged chef’s knives are well under $100, but many are $150 and up. A Japanese knife from a great craftsman can cost several thousand dollars. For most people, even $100 is probably out of proportion to the advantages, but a well-made object is a pleasure for its own sake. Price aside, a well-designed, well-made knife is faster, more precise, and more comfortable to hold. It’s less tiring to use for long periods. It takes and holds a very sharp edge.
For a long time, nearly every knife has been made of stainless steel. What makes steel steel, harder than plain iron, is the addition of a tiny amount of carbon. Seemingly insignificant amounts transform the metal, from less than 0.25 percent in low-carbon steel to as much as 1 percent or more in the high-carbon steel used for knives. To distinguish them from stainless, the staining blades are often called “high carbon,” but both stainless and staining are in fact high-carbon.
The simple addition of carbon makes high-carbon steel, both kinds, very hard — and yet also brittle. If you pry with a knife blade or twist it, the metal may snap dangerously. (Don’t do that with any knife. If it doesn’t break, it may get a permanent kink or bend.) Paradoxically, when it comes to sharpening, high-carbon staining steel behaves as if it were soft. That makes it easier to sharpen, and you might sharpen it more often. And, unlike stainless steel, it doesn’t tend to clog the surface of a sharpening stone. But the reason most of the costliest kitchen knives are made of tarnishing high-carbon steel is that the makers believe it takes a finer, therefore sharper edge.
Stainless steel, in contrast, not only resists corrosion, but it’s tougher because it further contains a large amount of chromium, from about 12 percent to as much as 18 percent in kitchen knives, plus a few percent more of elements such as manganese, nickel, silicon, vanadium, and molybdenum, each contributing particular qualities of hardness, brittleness, toughness, and wear resistance. The more carbon there is, the more chromium is required to maintain stainlessness, and the more chromium there is, the tougher the blade. (“Stainless” steel is a bit of a misnomer because the metal can become a little stained.) Generally, stainless steel is harder to sharpen, but once sharp, it stays sharp longer. Steels have evolved, however, so there are now some stainless steels that are as easy to sharpen as staining steel. The old generalizations don’t necessarily apply.
Sometimes you see the hardness of a blade described by numbers on the Rockwell C scale. That involves forcing a diamond-tipped cone into the metal and measuring the depth of the indentation. A good kitchen knife might be HRC 58 to 60, sometimes higher. The numbers are often a range, even for a particular knife, because the hardening of a blade isn’t easy to control. And Rockwell numbers tell only hardness, not brittleness, toughness (the opposite of brittleness), resiliency (the ability to return to shape), or wear resistance (how long the edge stays sharp in use). Steelmakers balance those qualities when they formulate a kind of steel; knife-makers do the same when they decide which one to use.
A brand-new staining-steel knife protected with a coat of oil looks as bright as stainless, impossible to tell apart. Use it for a couple of weeks, and it loses its sheen, turns dark and blotchy. To prevent rust, you have to wash and dry the blade immediately after each use. Besides the metal blackens when you cut acidic fruits, for instance, or onions, and unless you wipe it after each slice, it can leave a metallic taste. For most cooks stainless is best.
Which basic knife to start with? There are cooks who use a highly flexible filet knife for a lot more than fileting, and the blade is so thin that sharpening is quick. But there’s a lot it can’t do. A paring knife is handy, but most useful is a ten-inch (25-cm) chef’s knife or, for smaller hands, an eight-inch (20-cm). Anything shorter is inefficient for chopping (such as the rocking-chopping motion that makes fine pieces) or for slicing something large, such as a cut of meat or a loaf of bread. Beyond that, if you grip a knife with a thumb and curled forefinger on either side of the blade, then a bolster, either as part of the blade or clamped to it, protects your middle finger as it contacts the butt of the blade. I look for a thinner blade because it’s easier to sharpen and creates less friction in cutting, as long as it isn’t so thin that it wavers.
Some blades are ground more convex, others more concave, which reduces friction. With wear and sharpening, blades gradually become more hatchet-like. Slicing knives can benefit from having a line of ovals ground in to create air pockets, so slices fall away more easily. But with chef’s knives, sticking isn’t much of a problem, and grinding those divots requires a thicker blade. The finest handmade knives don’t have them.
There are Western-style chef’s knives, Japanese ones, and hybrids. Traditional Japanese knives are ground on just one side to form a 15-degree angle (which makes them either left-handed or right-handed). Western blades, ground on both sides, often to 20 degrees each with a final 15 degrees at the very edge to make a total of 30 degrees — a much wider angle, stronger but less sharp. Some hybrid knives are round to 15 degrees on one side with a small grind on the opposite side, also to 15 degrees. The santoku, with its Western influences, is the counterpart to a Western chef’s knife and may be beveled on both sides.
Always preserve the sharp edge of your knife by cutting on a soft, preferably wooden board.
This isn’t a consumer article comparing brands and particular knives, but if you’re going to own just one chef’s knife it should have a thin blade, not a hefty one and, reflecting the way you like to hold the knife, the butt of the blade shouldn’t dig into your skin: a metal bolster or a plastic part of the handle should protect you. For years I’ve frequently used a Victorinox plastic-handled chef’s knife (the ten-inch size now seems to be sold as a “carving knife”), and it’s fine. I prefer a curved French shape that allows an easy rocking motion — having started with French cooking, a Sabatier gives pleasure just through the association. But the first kitchen knife I ever bought, when I was in a college dorm and didn’t have a kitchen, was a wooden-handled Japanese knife I wish I still had, and if I were starting to explore knives for the first time, I might begin again begin with Japan, for the pleasure of experiencing another culture. To the right accomplished cook, the pleasure of cutting with a really well-crafted Japanese blade is worth the price. All my present chef’s knives started with 10- to 12-inch blades: the Victorinox, a matched pair of staining Thiers-Issard Sabatiers (a brand that isn’t currently exported to North America), a stainless Thiers-Issard, a staining Sabatier-syle Henckels from the 1950s or 60s (a style it later abandoned), a fat-bladed stainless Henckels from the 1980s, and a quince-handled, stainless, Japanese-made hybrid (that somehow, out of respect for its price, I almost never use). When you choose a knife, the ideal is if you’re lucky enough to have friends with knives of different sorts that they’ll let you try in their kitchen, is to do just that. ●
Based on an article in The Art of Eating issue 47; revised April 2022.
