<P><B>Abstract</B></P> <P>The effect of mechanical refining on the enzymatic digestibility of pretreated corn stover (PCS) was investigated. Low severity, dilute sulfuric acid PCS was subjected to mechanical refining using a bench-scale food processor blender, a PFI mill, a 12-inch laboratory disk refiner, and a 25mm co-rotating twin-screw extruder. Glucose yields from enzymatic hydrolysis were improved by 10–15% after blending and disk refining, while PFI refining and twin-screw extrusion showed a glucose yield improvement of 16–20%. A pilot scale refining test using a Szego mill was performed and showed approximately 10% improvements in biomass digestibility. This suggests the possibility to scale up a mechanical refining technique to obtain similar enzymatic digestibility glucose yield enhancement as achieved by PFI milling and extrusion technologies. Proposed mechanisms of each mechanical refining technology are presented and reasons for improvements in biomass digestibility are discussed in this paper.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We compared five different mechanical refining technologies on digestibility of PCS. </LI> <LI> We studied the effect of refining severity on digestibility of PCS. </LI> <LI> We explored the particle size and morphological change of biomass after MR. </LI> <LI> We did a pilot scale trial with Szego mill showing the possibility for scaling up. </LI> </UL> </P>