Hydrodynamic effect on the numbers of adhering Bacillus cereus spores before and after cleaning in place of part of a dairy processing line was investigated using nonintrusive flow characterization (local wall shear stresses and velocity profiles measurements). Geometrical changes, like gradual asymmetric pipe contractions and pipe expansions and bends, induce nonhomogeneous distribution of the initial and the residual soiling levels. Moreover, the recirculation zone resulting from the flow detachment after the expansion, allowed to explain the high level of adhered spores downstream of this geometrical change due to the generated shear stresses. The resistance to cleaning processes in the same zones is mainly governed by the adhesion strength of spores induced by the applied flow rate it? the contamination step. Welding and gasket areas, located at different positions in the loop, constituted deposit spots for spores and remained difficult to clean despite high-shear stress forces involved. (C) 2008 American Institute of Chemical Engineers.