The initial stage of a Green Biorefinery involves the fractionation of plant biomass into a fibre-rich press-cake and a nutrient-rich press-juice that are subsequently used to provide energy, chemicals and materials. However, limited information has been published to date on the factors influencing the fractionation of green biomass. Perennial ryegrass and cocksfoot silages harvested at two stages of maturity were subjected to hydrothermal conditioning at three temperatures (20, 40 and 60 C-degrees) with or without detergent. In a second experiment, Italian ryegrass and timothy silages harvested at three stages of maturity were subjected to three washing steps (30 min al: 60 degrees C in a 3 water + detergent (30 g L (1)): 1 silage ratio; undertaken 1, 2 or 3 times), before being mechanically pressed at three different pressures (1.5, 3.0 or 4.5 MPa). Overall, repeated washing (up to 2 washing steps) and mechanical pressing (3.0 MPa) proved the most effective treatments for the removal of solubles from a range of grass silages and in the isolation of a fibre-rich press-cake fraction. (C) 2012 Elsevier Ltd. All rights reserved.