In this study, a dimensional analysis of the continuous foaming operation by whipping was performed. Newtonian model fluids were formulated with controlled rheology and interfacial properties. The viscosity has been modified by changing the dilution of glucose syrup and surface tension has been modified by using two different surfactant species (whey protein and sucrose ester). Foams have been produced on an instrumented industrial rotor-stator mixer by varying the rotation speed, flow rates and pressure. An image analysis method which makes possible to characterize accurately the bubble sizes was performed on each samples. A dimensional analysis allowed to describe in a general way the foaming operation with dimensionless ratios and also enabled to weigh the magnitude of each operating parameter. A model which predicts bubble size, depending on process parameters and those related to the products has been established. This model offers a new definition of capillary number. The major influence of this number provides information on the mechanisms involved in the process. However, the approach also shows that other phenomena affect the bubble size. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.