The mis-named sharpening steel does not, technically speaking, actually sharpen a knife. Rather it hones the knife, aligning the edge so the knife cuts better.
Sharpening and Honing are Both Parts of Knife Care
We've all seen a chef quickly running the edge of a knife back and forth over a metal rod held in the other hand Some people mistakenly think this is sharpening, but it is not. It is a different process called honing or steeling.
The sharp edge of a metal knife is very thin and in normal use the tiny teeth on it can become bent over and distorted. This is on a microscopic level which you cannot see with the naked eye. The result is that the sharp edge of the knife is not contacting the food but rather is pointing in the wrong direction so the knife does not cut well. A quick honing will straighten the bent parts so the sharp edge is properly oriented once again and the knife cuts as it should—or at least a lot better.
What is Sharpening?
Sharpening is the process of removing metal to create a completely new edge on the knife. Even with regular honing the edge does eventually wear away and sharpening will be required. It is done by rubbing the dull edge on a fine abrasive surface such as a whetstone. This grinds away the metal until a new sharp edge is formed. It is essential that the knife be sharpened at the proper angle for the edge to form correctly.
Hone Often Sharpen Rarely
Regular honing—some people do it for every use—can keep a knife cutting well for a long time, weeks or even months. A lot depends on how you use the knife and the type of cutting board in use. When honing stops making a noticeable difference in how the knife cuts it is likely time for a sharpening.
Some Other Knife-Related Myths for You!
Think titanium cutting boards are better for your knives? Think again!
A sharp knife is one way to minimize tears when cutting onions.
