Fluid velocity, shear stress and shear rate at membrane wall exhibit profiles in complex geometries leading to more or less thick fouling layer. According to a reverse approach, mapping of fouling can be used as indirect tracer of velocity and shear stress profiles. Quantification of fouling due to proteins is interesting when working with alimentary fluids. To this aim, a novel technique based on FTIR-ATR has been developed for direct measure on membrane samples. The only requirement is the presence of polyethersulforte (PES) or polysulfone (PSU) in the membrane composition, as it is often the case. For demonstrative purposes, ultrafiltration of skimmed milk was carried out in two different module geometries: The first one was a flat RO membrane inserted in a circular vibrating housing (VSEP) of known shear rate distribution according to radius. The second one concerned a flat UF membrane inserted in a plate and frame transparent module allowing visualisation of velocity profiles. Then, mapping of protein deposit obtained by FTIR-ATR for two spiral UF membranes and one spiral NF membrane are shown. The results of the mapped protein distribution showed to be related with a shear rate expression for the VSEP and with CFD calculations for the plate and frame module. The technique was also validated by image analysis of charcoal deposits obtained through experiments with a charcoal suspension at the same hydrodynamic conditions. According to this, it can be said that protein mapping by FTIR-ATR is a reliable technique for autopsy purposes of membrane modules in the dairy industry. (C) 2008 Elsevier B.V. All rights reserved.