Semana de Engenharia 2010 Guimarães, 11 a 15 de Outubro CONTINUOUS FERMENTATION OF ALCOHOL-FREE BEER: BIOREACTOR HYDRODYNAMICS AND YEAST PHYSIOLOGY

Over the last years the development of new beer types such as alcohol–free beer has been increased. This development is motivated by the effort for a greater market share in the brewing industry and by the global trend to a healthier lifestyle without alcohol. Alcoholfree beer can be produced by removal of alcohol after regular beer fermentation or by methods that suppress alcohol formation. Suppression of alcohol formation or its early interruption, so that the alcohol content remains below 0.5 % (vol./vol.), is economically more attractive, since no additional equipment is necessary. Continuous fermentation using immobilized yeast cell systems have been developed successfully allowing the production of regular beer in as little as 2-3 days (Brányik et al. 2004). Similarly to regular lager beers, the production of alcohol-free beer can also take the advantage of continuous immobilized cell systems. In this case, only a short contact between yeast and the wort is required to remove the undesired worty offflavours (Van Iersel et al. 1995). However, continuous fermentation systems based on immobilized cell technology, have serious limitations as: (1) engineering problems (reactor design, optimization of operating conditions); (2) unbalanced beer flavour (altered cell physiology, ageing) and (3) unrealized cost (carrier price, unstable operation) (Brányik et al. 2005). In order to implement continuous fermentation systems for beer production, further development in reactor design and understanding of immobilized cell physiology, together with application of cheap, alternative carrier materials could provide a new stimulus to both research and application is required (Brányik et al. 2004). Being so, the main aims of this work are not only to understand and develop an appropriate system (carrier; reactor design, yeast strain) for immobilized yeast in order to produce alcohol-free beer continuously but also to determine and characterize the hydrodynamic behaviour of the reactor. The final objective is to understand the interaction between biofilm formation (immobilization method) and the reactor hydrodynamics in continuous alcohol-free beer