The water retained by the biomass after draining water but removed after vacuum filtration is water that is lightly bound or held by surface tension, but that can relatively easily be moved out of the biomass. For example, while bagasse with no partical size reduction absorbs 10.7 times its weight in water,vacuum can pull 70% of this bound water out of the biomass indicating that applying a force can move the lightly bound water.This suggests that a pressure differential in a biomass reactor can force water movement even if the solids concentration is above its saturation level. Interestingly, vaccum does not pull a significant of water out the saturated unwashed switchgrass whereas it pull out 45% and 94% of the bound water for washed and FT pretreated switchgrass, respectively.The very fine particles give the saturated unwashed switchgrass the consistency of mud and create a plug where no water can move. As the fines are removed during washing and the fibers structure is opened during pretreatment, there is more volume available for the water to move.