The influence of impeller design and operating conditions on the continuous manufacture of food foams was studied in a narrow gap mechanically stirred unit using a model food. Quality and texture of foams were characterised on the basis of density, bubble size and theological measurements. Mixing mechanisms were investigated using residence time distribution (RTD) experiments. The results show that mean bubble size in foams depends only on the intensity of viscous forces generated by the impeller. For a similar intensity of shear forces, impellers with a small internal volume are to be preferred for foaming because they improve bubble dispersion and mixing of surface-active agents. These allow the manufacture of foams with a lower density, which has been shown to improve their texture and increase their mechanical strength. RTD analysis is shown to be a simple diagnosis tool for estimating the mixing efficiency of new impellers which may be helpful in improving choice of adequate impeller design and operating conditions to produce foams with desired properties. (C) 2003 Elsevier Science Ltd. All rights reserved.