Burr grinders are now the standard for coffee grinding at home and in catering environments. They have many advantages over other forms of coffee grinding such as blade grinders, roller mills, and more traditional methods like pestle and mortars, grind stones or herb roller mills.
Burr grinders are faster than other manual forms of coffee grinders and far cheaper than industry grade machines like roller mills, while also being able to produce a more consistent grind quality than blade grinders.
Burrs are parts inside a grinder that crush the coffee beans into finer particles. Burrs come as two separate blocks, both with sharp ridged surfaces that face each other. When the grinder is activated, one burr spins while the other remains stationary. Coffee is fed into the narrow space between the two burrs and is cut and crushed by the spinning teeth. The shape, orientation, and distance between the two burrs dictates the size and quality of the grounds.
Most burr coffee grinders come with controls that adjust the gap between the burrs, so that users can adapt their grounds to their needs. Out of all the processes in coffee brewing, this control over the burrs probably has the most influence on the final cup. That is why burr grinders are so advantageous over other forms of grinding — they give the user much more control over the quality of their coffee.
There are two distinct types of coffee burrs. conical burrs vs flat burrs.
Most commercial coffee burrs are made of steel or ceramics. More expensive burrs might be coated with other metals (like titanium) to improve durability and sharpness.