Solid-state fermentation (SSF) has received more attention and has been applied to production of different products in recent years, especially biofuel production. The major problems to overcome in large-scale SSF are heat accumulation and heterogeneous distribution in a complex gas-liquid-solid multiphase bioreactor (or fermenter) system. In this work, a mathematical model of a rotating drum bioreactor for anaerobic SSF is developed considering the radial temperature distribution in the substrate bed. Validation experiments were conducted in a 5 m(3) pilot plant fermenter for production of fuel ethanol from milled sweet sorghum stalks. The model that was developed fit well with the experimental data. From these results, it was concluded that this mathematical model is a powerful tool to investigate the design and scale-up of an anaerobic SSF fermenter in the application of bioethanol production using cellulosic materials such as sweet sorghum stalks. (C) 2009 Elsevier Ltd. All rights reserved.