Tarhana, a fermented wheat flour-yoghurt mixture used in soup making, was produced in ready-to-eat form using canning. The effects of rotation speed (6.6-8.4 rpm) and retort time (3.2-3.8 min) on the viscosity of the samples were analysed using response surface methodology. Increasing rotation speed and retort time resulted in increased viscosity (p > 0.05). Retort time had more effect on viscosity than rotation speed. It is suggested that the regression equation can be used to estimate canning variables for the desired viscosity of the soup. (C) 2003 Elsevier Ltd. All rights reserved.