The well known multi-stage evaporation is an energy efficient process applied for concentrate juice production. There are however, some important issues concerning its thermodynamics which are not commonly revealed by the producers. The multi-stage design requires a properly designed control system to achieve maximum efficiency and capacity of the evaporator. In this paper, results of the author’s practical experience concerning the thermodynamics of the operation of the multi-stage evaporator in the industrial environment are presented. The report describes problems concerning the steady-state evaporator operation, choice of control parameters, and thermodynamics of the transient states.