Solid substrates were produced from the pretreated wood chips by disk milling (Fig. 1) under atmospheric conditions after the separation of the solids from the pretreatment hydrolysate using a screen. The pretreatment hydrolysates were saved for chemical composition analysis. The disk mill was equipped with plates of pattern D2-B505 (Andritz Sprout-Bauer Atmospheric Refiner, Springfield, OH).