Preprocessing is a crucial step in the utilization of biomass feedstocks for the production of fuel and biomaterials [1]. Size reduction and drying of the material, where used, are two of the most costly and energy intensive operations that are undertaken during preprocessing, reduction of the energy usage during these two phases will reduce cost of processing and ultimately reduce the overall cost to the final user. Traditionally, a hammer mill has been the primary method used for secondary size reduction. For wet material, a hammer mill requires high amounts of energy, while for dry material the hammer mill produces a large quantity of small particles [2]. In both cases, the costs increase either from additionally needed fuel cost or from the cost of lost material. In effort to lower the cost for size reduction, a rotary shear has been developed for the comminution of biomass feedstocks. The rotary shear utilizes interlocking, rotating disk that shear the material rather than using impact to reduce the particle size of the materials. Because the material is size reduced using a cutting motion, rather than impact, the distribution of particle sizes is much narrower than produced by hammer mills.