The effect of growth stage at harvest and of storage practice on the biochemical methane potential (BMP) of winter wheat was investigated using batch-fed stirred mesophilic digesters. The wheat used was a single variety sown at the same time (autumn) and harvested at 3 different stages in its growth: medium milk (A), soft dough (B) and Caryopsis (C). Wheats (A and B) were ensiled whilst the later harvested material (C) with a higher dry matter content was treated by the alkalage process. The BMP values expressed on the basis of volatile solids (VS) were 0.360 +/- 0.030, 0.346 +/- 0.006 and 0.311 +/- 0.016 I CH(4) g(-1) VS(added) for A, B and C, respectively. A simple first order kinetic model gave only a poor fit to the experimental data but a close match was obtained using a modified first order pseudo-parallel model which explains the methane production curve on the basis of differences in biodegradability of the plant material. (c) 2010 Elsevier Ltd. All rights reserved.