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In a Green Biorefinery processing green biomass, one possible application for the press-cake fraction is as biomass fuel for combustion. In an industrial setting, the preservation of herbage as silage and its subsequent fractionation into press-juice and press-cake fractions represent the two major process steps in the utilization of green biomass. This study investigated (i) the effects of ensiling and fractionation on the chemical composition of three common temperate grassland species harvested at different stages of maturity and (ii) the suitability of the herbage of these species for thermal combustion. The high contents of ash, N, Cl and K in perennial ryegrass, cocksfoot and red clover, at both pre- and post-ensiling, make these materials less suitable for combustion in certain applications. The loss of soluble/fermentable organic matter during ensiling increased the relative proportions of fibre, ash and N in the herbage, but these changes were relatively minor. In contrast, the substantial reduction in the concentration of compounds such as ash, N, Cl and K during fractionation improved the suitability of the press-cake fraction for combustion compared with the parent material. Press-cake prepared from later-harvested grass herbage with lower ash, S and N contents would be more suitable for combustion.