LONG-TERM STABILITY OF IMMOBILIZED YEAST COLUMNS IN PRIMARY FERMENTATION

The long-term operation of an immobilized continuous primary fermentat ion was studied. The system consisted of two packed-bed columns. The c arrier material was porous glass beads (Siran). An industrial wort and an industrial yeast strain were used. The pre-column was aerated with mixtures of synthetic air and CO2. Attenuation was stable during a co ntinuous run of more than 14 months. The percentage of dead cells in t he outflow from the main column varied between 7 and 42%. No problems with microbial contaminations were observed. The flavor compounds anal yzed indicated a balanced flavor close to that of a commercial Finnish lager beer. Statistically significant changes were observed only in e thyl acetate and propanol concentrations over the run time. A control strategy was developed based on changes in the gas feed into the preco lumn. Some flexibility in the capacity of the system also was observed .