AbstractA new type of reactor, an attrition bioreactor, was tested to achieve a higher rate and extent of enzymatic saccharification of cellulose than is possible with conventional methods. The reactor consisted of a jacketted stainless‐steel vessel with shaft, stirrer, and milling media, which combined the effect of the mechanical action of wet milling with cellulose hydrolysis. The substrates tested were newsprint and white‐pine heartwood. The performance of the reactor was excellent. The extent and rate of enzymatic hydrolysis could be markedly improved over other methods. The power consumption of the attrition bioreactor was also measured. The cellulase enzyme deactivation during attrition milling was not signific