This paper details the application of an iterative identification and control design methodology implemented in a modified form, which has been successful in improving the performance of a sugar cane crushing mill. The cornerstone of this iterative method is a frequency weighting derived from closed-loop input-output signals. The modified scheme includes a sequence of frequency-weighted controller design iterations using the initial plant model. After the controller performance has leveled out, a plant model re-identification is undertaken, followed by another series of controller designs. If plant model re-identification does not result in a controller with improved performance, the iterative design is terminated.