Acomparative evaluation of on-line control techniques was made for the glucose-controlled fed-batch culture of baker's yeast. Based on the comparison of control qualities by computer simulation, two methods -moving identification combined with optimal control and programmed-PI control-were adopted for the experiments to keep the glucose concentration in the culture broth at low level. The control variable was the feed rate of concentrated glucose. The glucose concentration in the culture broth was measured on-line every 5 min using an automatic glucose analyzer. The glucose concentration in the broth was controlled in the range of 0.1-0.2 kg/m3 with these control strategies.

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A turbidimeter (suspended solid concentration analyser: SSCA) which can measure directly the turbidity of culture broth has been developed. The SSCA was used to monitor baker's yeast and Escherichia coli fermentations. Although the medium conditions changed during the fermentations, the optical densities evaluated from the measurement of SSCA and predetermined calibration curves coincided well with those determined spectrophotometrically. Since SSCA can monitor microbial growth, it was applied to the control of glucose concentration in fed‐batch baker's yeast cultures by assuming a constant growth yield. Glucose concentration in the medium could be maintained between 0.2 and 0.3 g dm−3, and ethanol concentration was less than 4 g dm−3.