A mechanical device used for rupturing the cell walls of microorganisms to release their intracellular protein products. Laboratory-scale bead mills consist of a chamber filled with small glass beads and a suspension of the cells requiring rupture. The cell wall and membrane are disrupted by collisions between shear force layers generated by high-speed agitation and grinding action of the beads in the chamber. The vigorous agitation can lead to denaturation of released proteins due to the shear forces and local heating effects.