Results of the expert opinion poll were fed into the fuzzy inference system to codify the fuzzy rule base. Totally, 25 rules were created in the fuzzy rule base using the logic operators. Since the two input variables (DOM and PBK) simultaneously participated in the fuzzy decision making process, the AND logical operator was applied to create the fuzzy rules. The overall form of the fuzzy rule base is shown in (Table 1). It should be noted that in the formed fuzzy rule base, the term “is” in the consequent part of each rule that presents an imperative result. In other words, the consequents should be read as commands which must be done according to the information presented in the antecedent part of fuzzy rules. Hence, the term “is” in the consequent part is read as “must be changed to”. The FIS was implemented using Mamdani interface engine which utilizes the minimum method for the implication operation and the maximum method for the aggregation process (Lee, 2006). The results of aggregation process should be defuzzified to provide a real value indicating the “level” of pressure on the discharge section of the whitening machine. In this study, the centroid of area (COA) method was selected for conducting the defuzzification process.