The simpler, less effective grinder type that is easily available for grinding coffee is a blade grinder. This grinder type has a metal blade that spins at high velocity in a small chamber. When coffee is in the chamber, the blade chops the beans into smaller and smaller pieces. Since the coffee is trapped in the small chamber, some pieces get chopped more than others. Consequently, there is a significant range of particle sizes in the final product, leading to a less consistent brew extraction.
Did you know?
Elevation doesn’t have a direct effect on coffee quality, rather, temperature does.
Another concern about blade grinders is the risk of overheating the bean mass while grinding. Because the coffee is trapped in a small compartment under constant attack by high-speed metal blades, the temperature of the beans is elevated for the duration of the process. This extra heat drives off volatiles (including some we probably want to drink) and possibly, negatively influences the chemical composition of the beans. There’s no public research that examines the issue of the grounds heating up but, if it is an issue, then the blade grinder is guilty as charged.
The more complex, effective, and expensive grinder type is a burr grinder. Burr grinders have two metal pieces (burrs) that are maintained a set distance apart from each other. Coffee is added on top of the burrs. As one of the burrs spins, the coffee is ground.
When the particle is small enough to fit through the space between the burrs, it falls into a separate chamber below the burrs. Burr grinders not only achieve a higher uniformity of grind size, but they are easily adjustable, allowing for different grind sizes to be achieved for different purposes. Also, as the beans escape the grinding chamber right away, they aren’t subject to as much of an increase in temperature (although, if a large enough mass of beans are being ground, the heat generated from the burrs will likely be passed on to coffee later down the grind stream).
Both types of grinders have their advantages and disadvantages. As usual, there is no definitive correct answer. In general, consumers concerned about price and having a larger equipment footprint should probably opt for a blade grinder. Whereas a consumer with the available resources who is interested in a higher level of precision to produce a better of cup of coffee should probably acquire a burr grinder.
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