Grind Distribution Beats Grind Size

Grinders are compared by the size they produce, and recipes specify a setting as though it described the whole output. What actually leaves a grinder is a range of sizes, and the shape of that range matters enormously.

A setting sets a ceiling, not a size

The gap between the burrs determines the largest particle that can escape, so the setting effectively caps the coarse end of the distribution.

Everything smaller than that cap is also present, in proportions determined by how the coffee fractured on its way through.

Two grinders set to produce the same average size can therefore deliver quite different populations of particles.

A wide spread extracts unevenly by definition

Extraction rate depends on particle size, so a wide distribution guarantees that some material is over-extracted while other material is under-extracted at the same moment.

The cup contains both faults simultaneously, which is why it can taste bitter and sour at once and resist correction by adjusting the setting.

Narrowing the distribution raises the proportion of the coffee that is extracted well, which usually reads as increased sweetness and clarity.

Burr type shapes the distribution

Conical burrs tend to produce a distribution with a pronounced fine fraction alongside the target size, which contributes body and a heavier mouthfeel.

Flat burrs generally give a narrower spread with fewer very small particles, which is associated with clarity and separation of flavours.

Neither is superior in the abstract, and the preference tends to follow the brewing method and the character the drinker is looking for.

Speed and sharpness both matter

Fast-spinning burrs impart more energy and tend to fracture particles further after they have already reached the target size, widening the spread.

Sharp burrs cut cleanly, while worn ones crush and tear, which produces both oversized fragments and additional fines from the same setting.

This is why grind quality declines gradually as burrs age even though the setting mechanism continues to work exactly as before.

The cup is the practical test

Measuring a distribution properly requires sieves or laboratory equipment, which is beyond most home setups and rarely necessary.

A more accessible signal is how a brew responds to adjustment, since a narrow distribution gives clear predictable changes and a wide one gives muddled ones.

If moving the setting in either direction seems to make things worse in different ways, the spread rather than the average is likely the constraint.