Fines Are Unavoidable, And They Do Work

Grinding coffee never produces particles of a single size. A quantity of very fine material appears in every grind, and it is neither purely a defect nor something a better grinder eliminates.

Coffee fractures along existing weaknesses

The roasted bean has a cellular structure with walls of varying thickness, and it breaks preferentially where that structure is weakest rather than into uniform pieces.

Cell wall fragments and the contents of ruptured cells are released as extremely small particles regardless of how the burrs are set.

Because these come from the material itself, no adjustment removes them, and a coarser setting simply produces larger particles alongside a similar fine fraction.

Small particles extract disproportionately fast

Surface area rises steeply as particle size falls, so a fine particle gives up its soluble material in a fraction of the time a larger one takes.

By the end of a brew the fines are thoroughly extracted while the coarser particles are only partly so, which is the source of the mixed character in any cup.

An excess of fines pushes a brew towards bitterness and drying astringency even when the nominal grind setting looks correct.

They also contribute things worth having

Suspended fines add body and a perception of texture, and a brew from which they have been completely removed can taste thin and stripped.

In espresso they are essential, contributing to the emulsion and to the stability of the crema as well as to mouthfeel.

Sifting fines out entirely, which is possible, produces a clean and often strikingly clear cup that many people find lacking in weight.

Migration is the practical problem

During percolation, water carries fine particles downward through the bed until they lodge in the filter or against the bottom of the puck.

The accumulated layer restricts drainage, slowing the brew progressively and stretching contact time beyond what the recipe assumed.

Stalled pour overs and slow-running espresso shots are frequently a migration problem rather than a grind setting problem, and grinding coarser treats the symptom.

Grinder design changes the quantity

Burr geometry, sharpness and speed all affect how much fine material is produced at a given setting, though none reduce it to zero.

Blade devices chop rather than mill, producing a wide range of sizes including a great many fines, which is the core objection to them.

Comparing grinders usefully means comparing the width of the size distribution rather than the setting number, since the fine fraction is where they differ most.