This paper discusses the problem of controlling a multiple-stage industrial evaporator in a sugar factory. The control objectives are: syrup should have a sucrose concentration of 72%, the evaporator should produce the required amount of steam, and the steam consumption should be as low as possible. Achieving these objectives is difficult, due to the following plant features: strong disturbances, large time delays and many constraints. The control problem is solved by developing a physical model which is used as benchmark; then, a parametric identification is performed to obtain a control model. Finally, a successful real-time application of a multivariable GPC controller is presented.