This paper is concerned with stabilizing open loop unstable fluidized bed spray granulation with internal product classification by means of feedback control. Using the results of a detailed model analysis, that is, numerical bifurcation, controllability and observability analysis and a study of the gap metric, an appropriate combination of manipulated and control variables is proposed. Using a reduced transfer function model a robust controller is designed by means of H-infinity shaping methods. The controller is validated by simulation of the nonlinear plant model using an appropriate start-up strategy.