Biomass size reduction belongs to the high energy-consuming operations in industrial biofuel technologies. Its energy requirement actually ranges from hundreds to thousands of kilowatt-hours per ton of dry biomass. These high energy values are primarily caused by energy demand of disintegrators used for wet fibrous biomass. Therefore, the reduction of this energy requirement could significantly improve the whole process economics. Suitable disintegrators were searched and several potential industrial technologies of mechanical disintegration for wet fibrous biomass with respect to minimum energy demand were designed. Wet wheat straw served as model material to evaluate their energy requirements. The technology with the least energy demand was composed of a new, fully developed retting mill.