The present paper deals with the control of a Multi-Stage Continuous Fermenter (MSCF) used for the study of wine fermentation. The control design is facing three main difficulties: (1) system nonlinearity; (2) lack of on-line measurement of the controlled variable (sugar concentration); (3) positive constraints on the control inputs (inlet flow rates of each tank) coming from the cascade structure of the system. A control strategy has been proposed that accounts for these specificities. It is based on an input-output linearization control law coupled with an anti-windup technique and a state observer (Kalman filter). The strategy has been tested and validated first on numerical simulations and has then been applied to the real process. The experiments gave satisfactory results that open up new perspectives on the use of the MSCF.