The filamentous fungus Schizophyllum commune secretes a β-1,3- d-glucan branched at β-1,6. The resulting highly viscous culture suspension exhibits pseudoplastic flow behaviour. Power requirement, productivity and quality (expressed as specific shear viscosity) of aqueous glucan solutions were determined using agitators of the following types: Rushton turbine, helical ribbon, fundaspin and three fan impellers of different sizes. Using the fan impeller 64 with a ratio of impeller/vessel diameter of 0.64, both highest specific shear viscosity (200 mPa, 0.3 g l −1 glucan, 0.3 s −1, 20°C) and optimal productivity of 2.8 g l −1 d −1 were achieved during 30 l batch cultivations at a low aeration rate of 0.08 v/vm and constant impeller speed (100 rpm). A maximum rate of glucan formation of 8.8 g l −1 d −1 results when the impeller speed is gradually increased from 100 to 200 rpm at the point of oxygen limitation for providing a raised, but limited, oxygen supply. Due to its simple design the fan impeller is suitable for further scale-up.