- Availability: Specialty
No grinder produces a perfectly uniform particle size; every grind output has a distribution that includes some "fines" (tiny dust-like particles) and "boulders" (oversized pieces). Fines extract very quickly and disproportionately contribute to bitterness, astringency, and channeling in espresso; they also clog filter beds in pour-over. High-quality conical and flat-burr grinders produce a tighter distribution with fewer fines, which is one of the main reasons specialty bars invest heavily in their grinders.