Dried milled biomass samples are frequently utilised in small-scale batch digestion tests. However, herbage chemical composition can be altered by thermal drying, and this may affect specific methane (CH4) yields. Thus, the specific CH4 yield of herbage pre- and post-ensiling, prepared by two preparation methods were compared. Perennial ryegrass samples were either non-thermally dried (i.e. subject to cryogenic conditions, -196 degrees C) or thermally dried (40 degrees C), prior to milling. Specific CH4 yield was subsequently determined in a small-scale batch digestion test. Herbage pre-ensiling yielded 204 and 243 L CH4 kg(-1) VSadded and herbage post-ensiling yielded 212 and 188 L CH4 kg(-1) VSadded with non- thermal dried and thermal dried sample preparation methods, respectively. Due to opposing effects of thermal drying on CH4 yields of herbage either pre- or post-ensiling, it is not recommended to use thermal drying. Instead, it is recommended that non-thermal dried herbage samples are used in small-scale batch digestion tests. (C) 2014 Elsevier Ltd. All rights reserved.