Fines
What is fines in coffee?
Fines are the very small, dust-like particles that every grinder produces alongside the main grind. They extract quickly and can add body, but too many make coffee bitter and muddy. In unfiltered brews such as the French press, fines are what form the silt or sediment at the bottom of the cup.
A good burr grinder makes fewer fines than a blade grinder. In paper-filtered coffee, fines can also clog the filter and slow the drawdown. To reduce sediment in a French press, grind coarser, skim the crust, let the coffee settle and stop pouring before the last centimetre.