Micro-organisms on food contact surfaces provide a 'biotransfer potential', i.e. the ability to contaminate foods during processing or preparation. Surfaces coated with organic materials can act as sites for microbial attachment. This investigation into the surface properties of glass and poly(methyl methacrylate) substrates soiled with a milk powder, oil, and starch composite has found that fatty acid esters dominate the surface chemistry. A lower concentration of proteinaceous material was also detected, with the concentration dependent on both the underlying substrate and the thickness of the soiling material. The physical surface structure of the fouled surfaces showed a complicated surface topography with features of the order of tens of micrometres wide and up to 2 mu m high, which increased in size with increasing thickness of the soiling layer. The features reflect bulk incompatibilities between the components of the soiling material and demonstrate the heterogeneity of the surface as presented to micro-organisms.