Cellulosic biomass is reduced to a micropowder with particles having average diameters below 5-10 micrometers with a significant fraction of the particles have diameters below 1 micrometer. Biomass (e.g., wood, agricultural waste or other plant materials) is first processed into pieces having a maximum diameter of about 10 mm. This is then dried to reduce its water content to no more than about 15% by weight and introduced into a disruptor which reduces the particle size to about 1 mm. Next the biomass is processed with a disc mill where edges of rotating discs travel along a groove pressing and squeezing the biomass, thereby breaking the biomass pieces into smaller and smaller particles. The resulting micropowder is extremely susceptible to enzymatic or chemical hydrolysis into constituent sugars. In addition, the micropowder can be suspended in an air stream and burned directly to provide heat to boilers and similar devices.