Immobilized yeast shortens beer production time.

Immobilization in biotechnology involves restricting the free movement of cells or enzymes by fastening them to a solid carrier. When the cell or enzyme is bound to a solid carrier, the fluid surrounding the particle can move rapidly without washing away the cell or enzyme. This, in turn, facilitates continuous processing techniques.

Continuous beer fermentation has a long history, but only a few success stories. Scientists at VTT Biotechnology (PO Box 1500, FIN-02044 VTT, Finland) have undertaken much research on immobilized beer fermentation. Their research has often focused on the maturation process--secondary fermentation.

By using immobilized yeasts, researchers were able to remove a buttery off-flavor from lager beer during the maturation step. This involved first a slow chemical step and then an enzymatic reduction step inside the yeast cell. By designing a process in which these processes were separated--a heat step followed by an immobilized yeast step--the time for maturation could be shortened from about two weeks to one to two hours.

The next target of VTT researchers was immobilized primary fermentation. Their largest laboratory unit produces 0.5 L/hour of beer. They have been able to run the system for more than 440 days without encountering any problems. The production of major aroma compounds was stable. Investigators were able to control the formation of major aroma compounds by changing gas feeds into the first reactor.

Long-term operational stability and the use of inexpensive carrier materials helped make possible larger-scale experiments in primary fermentations. VTT's industrial partners have designed and built pilot or semi-industrial sale systems to further investigate the feasibility of continuous, immobilized primary fermentation.

The industrial units produce 600 L/day to 1200 L/day, and the first results are encouraging.

Further information. Ilkka Virkajarvi; phone: [phone]; fax: [phone]; email: [e-mail].