This report illustrates that infra-red reflection absorption spectroscopy (IRRAS) is a new powerful and promising technique to obtain detailed molecular information of biomolecules at and near the air/water interface of complex food solutions. Here it is demonstrated that in combination with spectral simulation, this technique can provide information on local concentration, conformation and orientation of different constituents simultaneously. Furthermore, dynamics of, e.g. protein accumulation and unfolding at the interface, can be studied on-line. Molecular properties can be measured together with system parameters, such as surface pressure, pH and ionic strength, and as a function of process, like expansion or compression the surface.