STATE-OF-THE-ART AND FUTURE-DEVELOPMENTS IN FERMENTATION

The objective of process optimization in brewery fermentations is to build up yeast concentrations sufficient to gain an optimal rate and extent of attenuation and desired flavor development, while balancing, but not overexpending, wort nutrients for growth and maintenance. In terms of process economics, two alternatives exist-moving to greater volume accelerated-batch processing and applying small-scale, high-rate fermentation systems that are capable of being stepped up to meet peak output when necessary. In the standard batch process, volumetric productivities are controlled mainly by cyclic variations in growth and fermentation rates and by the amount of yeast in suspension as a result of the gas-lift action taking place in the fermentor. Thus, fermentor design must be optimized with respect to agitation and yeast concentration. Reduced process times may be achieved in cylindroconical vessels because of increased movement within the fermentor. Unfortunately, high degrees of agitation have been shown to give flavor problems. The adverse effects of agitation on beer quality may be prevented by operating under fed-batch conditions. Another approach to improve volumetric productivity is cell immobilization. With the successful application of immobilized yeast reactors for continuous beer maturation, as well as for the production of low-alcohol and nonalcoholic beers, one can expect an increasing contribution of immobilized yeast systems to the development of a new process area in the brewing industry.