An extractive fermentation process for 6-pentyl-alpha-pyrone (6PP) production by Trichoderma harzianum was scaled-up from 500 ml shake flasks to 10 1 stirred tank bioreactors keeping constant the volumetric power drawn (P/V). Two general effects of Mover 6PP production were observed: at the low P/V cultures (from 0.08 to 0.4 kW/m(3)) a gradual increase in P/V improved 6PP production; meanwhile, at P/V values above 0.6 kW/m(3) 6PP concentration was significantly reduced due to higher hydrodynamic stress. Overall, maximum 6PP production (230 mg/l) was a function of P/V regardless of the cultivation scale. However, agitation with impellers triggered an earlier synthesis of 6PP in the 10 1 bioreactor cultures, if compared to their shake flask counterparts. This suggests a physiological mechanism through which this fungus responds to hydrodynamically stressful conditions. (c) 2006 Elsevier Ltd. All rights reserved.