Vol. IV · Knives, Tools and the Work Space Plate 1 of 10knife, chef's knife, cleaver, santoku, edge angle, bevel, steel hardnessTM

The Knife.

A knife is a wedge. The thinner the wedge, the less it pushes the food apart — and the more easily it bends or chips.

Every kitchen knife is a wedge of steel ground to an edge. How easily it cuts depends mostly on how thin the wedge is just behind the edge: a narrow angle parts the food with little force, a wide one shoves it apart and crushes. But a thin edge is fragile. European chef's knives are commonly sharpened to about 20° on each side; Japanese knives, made of harder steel, to about 15° or less; a single-bevelled Japanese blade is ground on one side only. The Chinese cleaver (菜刀) — despite its look, a slicing knife for most of its work — sits between.

Steel hardness, measured on the Rockwell C scale, is the other half of the trade: harder steel holds a thin edge longer but chips more easily if twisted or used on bone. The workshop draws the edge at the angle you choose and measures what that angle means for the food.

Below: the blade in section at the angle you choose, and how wide the wedge is one millimetre and five millimetres behind its edge.

What you will learn
Workshop
A blade in section with the edge angle you choose (per side; total for a single bevel). The wedge width behind the edge is 2·d·tan(angle) for a double bevel, d·tan(2·angle) for a single one.

Thin cuts easily, thick lasts

At 20° per side — a typical European chef's knife — the blade is 0.73 mm thick one millimetre behind the edge; at 15°, typical for a Japanese gyuto, 0.54 mm, so the European edge is 1.36 times as thick where it meets the food. A heavy cleaver for chopping bone may be ground to 25° or more (0.93 mm). The thinner edge slips through a tomato skin or raw fish with less force and less crushing; the thicker one survives the board, the bone and the occasional twist.

For a home cook the practical choice is a chef's knife or a Chinese cleaver of 18–22 cm for almost everything, a small paring knife for hand work, and a serrated knife for bread and ripe tomatoes, whose teeth cut where a smooth edge would skid. Whatever the knife, the edge angle is a choice you make every time you sharpen (IV.6), and a sharp knife is the safer one: it goes where it is guided, without the force that makes a dull blade slip.

At the stove

Slice a ripe tomato with your sharpest knife and with your dullest, without sawing. The sharp one parts the skin with almost no pressure; the dull one pushes the tomato flat first. That extra force is what makes dull knives dangerous.

The Chinese cleaver (菜刀) does duty as knife, scraper, crusher and spatula: its broad blade carries cut food to the wok, its flat smashes garlic and ginger, and its spine pounds meat.

Terms

Edge angle
The angle between the bevel and the blade's centre line; the included angle is twice it for a double-bevel edge.
Bevel
The ground face that forms the edge.
Single bevel
An edge ground on one side only, traditional for many Japanese knives.
Rockwell hardness (HRC)
A measure of steel's hardness; kitchen knives range from about 55 to over 62.
A knife is a wedge: a thin edge cuts with less force, a thick one survives more abuse. Keep it sharp; a sharp knife is safer.

Sources

  1. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.