Boulders

Oversized particles (500+ microns) produced when the burrs can't cut beans cleanly. Boulders are the largest end of the particle-size distribution.

Why it matters — Boulders under-extract — they release only surface compounds during a normal shot, contributing sourness or grassiness rather than the balanced sweetness of properly extracted grounds. High boulder counts usually mean dull or misaligned burrs.

Good to know

• Common after burrs reach end of life (typically 500–1000 kg for flat burrs, more for conicals).
• Misalignment can produce boulders even with new burrs — check parallelism with the marker-pen method.