Long-term stability of immobilized yeast columns in primary fermentation

The long-term operation of an immobilized continuous primary fermentation was studied. The system consisted of two packed-bed columns. The carrier 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 CO(2). Attenuation was stable during a continuous run of more than 14 months. The percentage of dead cells in the outflow from the main column varied between 7 and 42%. No problems with microbial contaminations were observed. The flavor compounds analyzed indicated a balanced flavor close to that of a commercial Finnish lager beer. Statistically significant changes were observed only in ethyl acetate and propanol concentrations over the run time. A control strategy was developed based on changes in the gas feed into the pre-column. Some flexibility in the capacity of the system also was observed.