BACKGROUND: Heat removal is one of the major constraints in large-scale solid-state fermentation (SSF) processes. The effect of internal air circulation by forced convection on heat and water transfer has not been studied in SSF tray bioreactors. Formulation of a mathematical model for SSF requires a good estimation of the mass and heat transfer coefficients. RESULTS: A stainless steel tray bioreactor (80.6 L capacity) was used. Aspergillus niger C28B25 was cultivated under SSF conditions on an inert support. Temperature, moisture content, biomass and substrate concentrations were measured. Water and energy integral balances were used to estimate the heat and mass transfer coefficients involved in the process. The Reynolds number (N(Re)) in the headspace of the tray bioreactor ranged from 2.5 to 2839, which increased the global heat transfer coefficient from 4.2 to 6.9 (Wm(-2) K(-1)) and the mass transfer coefficient from 1.0 to 2.1 (gm(-2) s(-1)). Mathematical model predictions of the temperature and moisture content of the fermentation bed showed a high goodness-of-fit with the experimental results. CONCLUSIONS: This is the first report describing the effect of N(Re) of air in the headspace of a SSF tray bioreactor on the heat and mass transfer coefficients and temperature regulation in SSF. (C) 2011 Society of Chemical Industry