There are two kinds of coffee grinders: blade and burr. Between them, burr grinders are much preferred over blade grinders, because burr ones provide a more consistent grind.
Blade Grinders Provide Inconsistent Grinds
Blade grinders are like food processors or blenders designed for coffee beans. They have sharp blades (hence their name) that chop up beans.
These grinders provide minimal control and inconsistent results. They don’t have any settings for fine, medium or coarse grinds. You can only control how long beans are ground for, which gives you a little control over the grind’s fineness.
No matter how long you grind beans for, though, they will never be a uniform size. Because beans remain in one chamber and are chopped multiple times, some beans will be ground more finely than others. For instance, one bean might be chopped 100 times, but another bean might only come into contact with a blade 15 times. There’s no way to compensate for this with a blade grinder.
Burr Grinders Provide Consistent Grinds
Burr grinders, in contrast, provide consistent grinds. They have an upper chamber, a lower chamber, and two burrs, which are abrasive, hard surfaces that grate against each other. As beans pass from the upper to the lower chamber, they are ground by the burrs. Because each bean passes through only once, every coffee bean is ground to the same size.
With a burr grinder, you can select how fine or coarse you’d like your grounds. As the grind setting is changed from fine to coarse, the burrs are moved further apart so that larger grinds can pass through them. On a finer grind setting, the burrs are kept close together, and only small grinds will drop to the lower chamber. Until the beans are the correct size, they’ll keep getting ground by the burrs, but as soon as the beans are ground to the proper size, they’ll drop to the lower chamber
With a burr grinder, you will not only have freshly ground coffee, but it will also be uniformly ground. This will provide even extraction during the brew process and produce the best cup of coffee.