Burr coffee grinders crush coffee beans between a moving grinding wheel and a non-moving surface. The positioning on the burr is what regulates the ground size, allowing for consistent grinds. Usually only one of the metal burred pieces moves, but in some models both move against each other.
There are two types of burr grinders. The wheel burr and the conical burr. The former is less expensive, and has wheels that spin very fast making a lot of noise. Also the speedy rotation makes for more mess.
The conical burr grinder is really better. Spinning slower, its quieter and less messy. It is actually very good for oily or flavored coffees as the grounds do not clog. Its high price is justified for its quality and efficiency.
Burr grinders work simply. Two pieces of burred metal that may be flat or conical in shape lie on top of one another or inside one another as in conical burrs. The metal pieces rub together the beans that pass through with the grounds being mashed out into a hopper or a chute.
The closer each burred piece of metal is to the other, the finer is the resulting coffee grain. The calibration of the burr wheels decides the even granule size. When grinding for an espresso machine, top-of-the-line burr grinders are better.
