Abstract: The present invention provides novel techniques for controlling biofuel production processes. In particular, estimated yeast activity values are determined by yeast activity sensors. These estimated yeast activity values are used to bias predicted yeast activity values from an inferential dynamic predictive model. The biased predicted yeast activity values are in turn used to control a fermentation sub-process of the biofuel production process, while also be used to update the inferential dynamic predictive model, to maximize yeast activity in the fermentation sub-process. Maximizing yeast activity and yeast growth in the fermentation sub-process leads to the maximization of biofuel production in the biofuel production process.