The present application relates to a fermentation method comprising mixing in a medium xylose, one or more fermenting microorganisms, and an ionizing radiation irradiated cellulosic or lignocellulosic material, fermenting the xylose to a fermentation product, wherein the fermentation step produces fermentation product at a faster rate than would be produced in the fermentation step in the absence of the irradiated cellulosic or lignocellulosic material.