In the overall plant constraints, it is intended to keep syrup brix between 50° and 72°bx. Thus when this brix constraint was approached, the controller increased the clear juice flow rate, the only remaining input variable move, in order to bring the syrup brix back under control. A similar effect was observed for the case where the disturbance censed a decrease in syrup brix, e.g. a decrease in juice temperature. In this case, the v2 throttling valve was opened until it encountered a constraint (100% open) and then the clear juice flow rate was reduced, to prevent the syrup brix from falling below its constraint of 50°bx.