Understanding the extraction process will enable you to learn how to brew coffee successfully. First, the grind (aggregate size) of the coffee is crucial. The finer the grind, the more surface in relation to mass is exposed to the hot water. An un-ground coffee bean has the least amount of surface area in relation to mass, and would be impossible to brew successfully.
The tendency is to assume that the more finely coffee is ground, the better the resulting infusion will be. If the grind is too fine, and the exposure too long, you’ll get much more than you want. Over-extraction of the aggregate will dissolve too many of the undesirable compounds, generally referred to as “bitters”. The trick is to get just what you want out of the coffee, and no more. Typically, a fine grind is used for espresso, a medium grind for a home brewer and a coarse grind for a French press.
Blade grinders are inexpensive but produce a very inconsistent grind size. Even if you’re trying to get a course grind, you will still get some powder. Blade grinders are nothing more than little blenders that slice, tear, and smash the coffee beans. Worse yet … since the blades are spinning at a very high RPM, it is very easy to burn the coffee. You’ll have to experiment with any particular blade grinder to achieve the desired results. As a rule, you don’t want to grind for more than 20 seconds or you risk burning the ground coffee. If you are grinding a small amount of beans, you should shake the grinder as it is grinding. When grinding three ounces of beans the blade grinder will produce the best results, because the aggregate produces good resistance to the blades and a natural flowing circulation of the aggregate occurs.
The old-fashioned hand grinders known as burr grinders are excellent, and they don’t cost much more than blade grinders. These grinders have not been significantly improved upon since they came into existence. They’re slow (about a minute for one cup), but produce a very consistent grind, and there is no chance of burning the coffee. They are still made today, and size of the grind can be adjusted from very course to powder.
Disc and Conical
Disc and conical grinders provide the most precise grinding. These grinders have serrations or grooves cut into the discs or cones. The coffee beans fall in between the two discs or cones, one of which turns while the other remains stationary. The sharp edges of the grooves are what cut the beans and result in the most consistent grind. These are the grinders of choice for high quality coffee, but they are quite expensive.