The effectiveness of wheat straw fine to ultra-fine grindings at pilot scale was studied. The produced powders were characterised by their particle-size distribution (laser diffraction), crystallinity (WAXS) and enzymatic degradability (Trichoderma reesei enzymatic cocktail). A large range of wheat-straw powders was produced: from coarse (median particle size similar to 800 mu m) to fine particles (similar to 50 mu m) using sieve-based grindings, then ultra-fine particles similar to 20 mu m by jet milling and similar to 10 mu m by ball milling. The wheat straw degradability was enhanced by the decrease of particle size until a limit: similar to 100 mu m. up to 36% total carbohydrate and 40% glucose hydrolysis yields. Ball milling samples overcame this limit up to 46% total carbohydrate and 72% glucose yields as a consequence of cellulose crystallinity reduction (from 22% to 13%). Ball milling appeared to be an effective pretreatment with similar glucose yield and superior carbohydrate yield compared to steam explosion pretreatment. (C) 2011 Elsevier Ltd. All rights reserved.