On-line estimation and control of apparent extract concentration in low-malt beer fermentation

Apparent extract concentration, which is defined as the apparent total dry matter concentration in the media calculated by measurement of the specific gravity, is a very important variable in the process of beer and low-malt beer fermentation. In the present study, ethanol formation and the residual apparent extract concentration were estimated using the CO 2 concentration in the exhaust gas. A simple mathematical model involving the CO 2 production rate, temperature and cell activity was constructed and a novel system for on-line estimation and control of apparent extract concentration was developed. In the control system for the residual apparent extract concentration, cell activity was estimated by monitoring the differences in actual CO 2 production rate. In addition, the future trajectory of the apparent extract concentration was predicted. The degree of fermentation, i.e., the residual apparent extract concentration trajectory, was controlled by raising or lowering the temperature, taking into account the estimated cell activity at that time. The residual apparent extract concentration reached the target value at a given time, using the on-line estimation of apparent extract concentration and temperature control.