Standard testing of enzyme hydrolysis of biomass is most often performed in shake flasks with orbital mixing (NREL LAP-009).  Mixing of high solids content or poorly treated biomass represents a challenge for orbital mixing.  This is sometimes addressed by impellers more suitable for low viscosity liquids or by lift-and-drop mechanisms (e.g. cement mixers) not scaled for the laboratory.  We built a small and inexpensive tumbler that is analogous to efficient lift-and-drop systems for testing enzyme hydrolysis simultaneously on multiple samples, and demonstrated that poorly treated biomass is more efficiently hydrolyzed by rough mixing than by the standard laboratory process.