Immobilized yeast bioreactor systems for continuous beer fermentation

Two different types of immobilized yeast bioreactors were examined for cont inuous fermentation of high-gravity worts. One of these is a fluidized bed reactor (FBR) that employs porous glass beads for yeast immobilization. The second system is a loop reactor containing a porous silicon carbide cartri dge (SCCR) for immobilizing the yeast cells. Although there was some residu al fermentable sugar in the SCCR system product, nearly complete attenuatio n of the wort sugars was achieved in either of the systems when operated as a two-stage process. Fermentation could be completed in these systems in o nly half the time required for a conventional batch process. Both the syste ms showed similar kinetics of extract consumption, and therefore similar vo lumetric productivity. As compared to the batch fermentation, total fusel a lcohols were lower; total esters, while variable, were generally higher. Th e yeast biomass production was similar to that in a conventional fermentati on process. As would be expected in an accelerated fermentation system, the levels of vicinal diketones (VDKs) were higher. To remove the VDKs, the yo ung beer was heat-treated to convert the VDK precursors and processed throu gh a packed bed immobilized yeast bioreactor for VDK assimilation. The fini shed product from the FBR system was found to be quite acceptable from a fl avor perspective, albeit different from the product from a conventional bat ch process. Significantly shortened fermentation times demonstrate the feas ibility of this technology for beer production.