Fines

Fines are the very smallest particles created when you grind coffee: the powdery dust at the bottom of the size range. No grinder produces a single uniform size, so every grind contains a mix of fines, mid-size particles, and the largest boulders. Even a good burr grinder makes some fines; the goal is fewer of them, not none.

Why they matter cuts both ways. Fines have huge surface area for their size, so they extract fast and contribute body, sweetness, and a fuller mouthfeel. That is part of what gives a well-ground cup its texture. But in excess they cause trouble: in percolation brews they migrate down and pack into the filter, slowing or stalling the drawdown, and because they extract so quickly they tend toward bitterness while the rest of the bed lags.

Cheap blade grinders make far more fines than a quality burr grinder, which is the main reason burrs are recommended. See grind-size-guide for how this shapes your settings. Some brewers sift fines out to chase clarity, though most home drinkers simply choose a grinder that makes fewer.