Nanotiltration (NF) of silage juice from a green biorefinery was investigated as a first step to purify lactic acid and amino acids which are seen as valuable products. The performances of three organic NF membranes (PES 10, N30F and MPF36) as well as one ultrafiltration (UF) membrane (PES004H) were compared by experiments in a stirred batch cell. Cross flow trials with two inorganic membranes (UF Tami, NF Inocermic) completed the membrane screening. Special attention was directed to the retention of free amino acids, lactic acid, sugars, salts and colouring substances. Nanofiltration showed average fluxes of up to 6.5 L m(-2) h(-1). Decolouring amounted to 80-99%. The membrane screening resulted in a recommendation for one NF membrane (PES10) with adequate specific separation properties. The UF membrane PES004H showed high transmission properties for amino acids and lactic acid in combination with noticeable specific separation properties for colouring substances. (c) 2005 Elsevier B.V. All rights reserved.