The present paper contributes to the application of the coupled CFD-DEM approach (CFD - Computational Fluid Dynamics; DEM - Discrete Element Method) for the simulation of the separation process of grain and material other than grain (MOG) in the cleaning device of a combine harvester. The large number of influencing factors, their interactions, the wide range of scatter of properties, which are typical for biogenic particles, and the resulting complexity of the separation process require a strategic approach for the creation of a valid simulation model. The study presented in this paper investigates the separation process therefore at two levels, which differ by the degree of process abstraction. The numerical results prove the applicability of the numerical method by the comparison to corresponding experiments in general. However, deviations can also be identified which emphasize the need for further research to improve parameterization and modeling.