Fines

Very small particles (under ~100 microns) produced as a byproduct of grinding.

Category: Extraction — Workflow & Technique

The smallest particles produced by the grinder — typically under 100 microns. Some fines are unavoidable; the proportion of fines depends on burr type, alignment, and the bean.

Why it matters — Fines over-extract quickly because their surface area is so high relative to volume. Too many fines means bitter, astringent extraction. Some fines are necessary for body and crema in espresso.

Good to know

Conical burrs typically produce more fines than flat burrs of the same diameter; this is part of why conicals taste sweeter and have more body.
Burr alignment matters — misaligned burrs produce excessive fines on one side and excessive boulders on the other.