Conventional control systems can not give satisfactory results in fermentation systems due to process non-linearity and long delay time,. This paper presents design and simulation a fuzzy controller for industrial fed-batch baker's yeast fermentation system in order to maximize the cell-mass production and to minimize ethanol formation. Designed fuzzy controller determines an optimal substrate feeding strategy for an industrial scale fed-batch fermentor relating to status of estimated specific growth rate, elapsed time and ethanol concentration. The proposed controller uses an error in specific growth rate (e), fermentation time (t) and concentration of ethanol (Ce) as controller inputs and produces molasses feeding rate (F) as control output. The controller has been tested on a simulated fed-batch industrial scaled fermenter and resulted in higher productivity than the conventional controller.