How to Sharpen a Knife

Whetstone Fundamentals for the Professional Kitchen

A sharp knife is a chef's primary tool, critical for precision, speed, and safety on the line. J. Kenji López-Alt demonstrates the essential techniques for manual knife sharpening using waterstones. Rather than relying on mechanical pull-through sharpeners that strip away excessive steel, the focus is on mastering the manual control of the blade's edge angle on a whetstone. Understanding this process allows chefs to maintain their kit to exact specifications, extending the lifespan of their most valuable tools.

The core of the technique lies in establishing a consistent angle between the blade and the stone. For most Western knives, this is typically around 15 to 20 degrees, while Japanese blades often require a shallower angle. Maintaining this angle throughout the stroke is the most challenging aspect for beginners. The guide addresses this by emphasising muscle memory and stable hand placement, ensuring the blade glides smoothly from heel to tip.

Detecting the Burr and Polishing the Edge

A key indicator of successful sharpening is the formation of a burr—a microscopic wire edge that develops on the opposite side of the blade being ground. Chefs learn to feel for this slight ridge with a thumb stroke away from the edge. Once a consistent burr is established along the entire length of the blade, the knife is flipped to repeat the process on the other side.

After establishing the edge on a medium-grit stone, the process transitions to a finer grit for polishing and refining. This stage removes the scratch marks left by the coarser stone and refines the micro-teeth of the blade, resulting in a clean, sharp finish.

Honing versus Sharpening

It is vital to distinguish between sharpening—which actually removes metal to create a new edge—and honing, which uses a steel to realign a bent edge. Honing should be done daily to maintain performance, but when the edge is truly dull, only a whetstone can restore the bevel. Regular, disciplined maintenance on stones prevents the need for drastic, metal-stripping repairs later on, keeping your knives peak-ready for every service.