Since the early use of automatic control, partial control strategy has frequently been adopted in complex chemical processes having more process variables than manipulated variables. The key idea of partial control strategy is to find the dominant variables such that when they are controlled to constant setpoints, one can ensure the variations in the operating objectives are acceptable in the face of external disturbance occurrence. Although the idea seems simple to understand, the identification of the dominant variables can be a daunting task where presently this is largely done through the application of extensive process knowledge and experience. In this paper, we present a novel methodology based on Principal Component Analysis, which can provide an avenue to the engineers to conveniently identify the dominant variables without the need for extensive process knowledge and experience. The effectiveness of the methodology is demonstrated based on the control structure design of a complex extractive fermentation process.