RAPID FERMENTATION OF BEER USING AN IMMOBILIZED YEAST MULTISTAGE BIOREACTOR - CONTROL OF SULFITE FORMATION

The characteristics of yeast sulfite metabolism in a multistage biorea ctor system for beer fermentation were investigated. No sulfite was pr oduced in the continuous stirred-tank reactor (CSTR). However, large a mounts were produced in the packed-bed reactor (PBR). Production of su lfite in the PBR seems to be inevitable when it is operated continuous ly. In order to control the sulfite level in the young beer, the yeast needs to be reactivated into the growth phase. One possible strategy to achieve this is to aerate and periodically remove yeast clogged in the reactor once every 6-7 months before the sulfite level exceeds a g iven concentration (e.g., 20 mg/L). It was confirmed that sulfite prod uction is closely related to the growth condition of the yeast and is therefore important to consider in the control strategy for sulfite wh en using the immobilized yeast reactor for beer production.