A technique for pyrolyzing biomass materials is disclosed wherein a hot surface is provided having a predetermined temperature which is sufficient to pyrolyze only the surface strata of the biomass material without substantially heating the interior of the biomass material thereby providing a large temperature gradient from the surface strata inwardly of the relatively cool biomass materials. Relative motion and physical contact is produced between the surface strata and the hot surface for a sufficient period of time for ablative pyrolyzation by heat conduction to occur with minimum generation of char.