A blade grinder produces a very inconsistent grind by chopping/cutting the coffee beans. The fineness of the coffee is controlled by time. Unfortunately, finer grinds will settle at the bottom and coarser chunks rise to the top during grinding. Inconsistent grind particle size is a problem as the finer particles will extract much more quickly than coarser particles. The finer particles will start to produce unpleasant bitter components while the larger particles are still producing pleasant components. The resulting coffee will include bitter components from over extracted coffee (from fines) and dull, under-extracted coffee from the coarser particles. This isn’t a pleasant mix and will vary greatly from cup to cup.
A burr grinder crushes the beans as they move from the top hopper, through the burrs, and into the catcher. The grind size is determined by the distance between the outer, and inner burrs. This distance is fixed, and so the burr grinder offers much greater consistency in grind particle size. This produces much more evenly extracted, consistent and better tasting coffee.
