The aim of this work was to investigate the rheological behaviour of liquorice extract to design properly and to optimise a single screw extruder dedicated to liquorice production. A stress-shear rate law was determined and a simplified analysis of the extruder performance was carried out. The velocity profiles in the extruder channel were determined by using a numerical method, while few geometrical parameters, like the channel depth and the helix angle, were optimised to obtain the maximum flow rate as a function of different operating conditions. A power law relationship between either the flow rate or the power consumption and the screw speed was established. The deviation from linearity was expressed by an exponent which. in all the cases examined, was found to be almost constant and ranging from 1.22 to 1.30. (C) 2001 Elsevier Science Ltd. All rights reserved.