Why is my coffee grind size inconsistent?

The pursuit of a 'unimodal' grind—where every particle is identical in size—is the holy grail of coffee preparation. When a grinder produces a wide range of particle sizes, it creates 'differential extraction.' In this scenario, the smallest particles (fines) extract almost instantly, contributing bitterness and astringency, while the largest particles (boulders) remain under-extracted, resulting in a sour, thin, or muddy cup. The mechanism of inconsistency is often mechanical: if the burrs are not perfectly parallel, the gap between them fluctuates as they rotate, causing the grinder to cut some beans finer than others. While many focus on the motor, the true culprit is often the tolerance of the carrier assembly. From the producer's perspective, the physical structure of the bean—its density, moisture content, and cellular integrity—dictates how it fractures under stress. A brittle, light-roast bean shatters differently than a dense, high-altitude bean, meaning a grinder calibrated for one may struggle with the other. A common misconception is that 'fines' are always a sign of a bad grinder; in reality, some fines are necessary for body, but they must be produced predictably. The goal is not to eliminate fines, but to eliminate the chaotic, unpredictable distribution caused by burr wobble, heat-induced expansion of the grind chamber, and static electricity that causes grounds to clump together before they even hit the brew bed.