INFLUENCE OF SUBSTRATE DISTRIBUTION ON PRODUCTIVITIES IN COMPUTER CONTROLLED BAKER'S YEAST PRODUCTION

In recent years considerable emphasis has been placed on the application of computer control to substrate feeding in baker's yeast production. Many investigators have studied the dynamics of different control loops and also first steps have already been taken to optimize the control algorithms. As far as the experimental verification of different strategies is concerned, the published work is, however, restricted to laboratory scale only. From current practice in baker's yeast industry which is most often based on open loop control with fixed schedule for carbon substrate addition, it is well known that mixing of substrate is playing an important role. The effects of the dynamics of mixing process in mechanicaly stirred tanks upon the performance of baker's yeast fermentation with fixed schedule have been investigated earlier by using a circulation model (Bajpai and Reuss, 1982). In the present contribution this framework is used in conjunction with a closed computer control of carbon substrate feeding based on exhaust air analysis. From experimental results for computer controlled fermentation in 10 and 20001 scale a decrease of productivity with increasing circulation times of liquid is observed. These results can be confirmed with the model calculations.