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

The objective of process optimization in brewery fermentations is to b uild up yeast concentrations sufficient to gain an optimal rate and ex tent of attenuation and desired flavor development, while balancing, b ut not overexpending, wort nutrients for growth and maintenance. In te rms of process economics, two alternatives exist-moving to greater vol ume accelerated-batch processing and applying small-scale, high-rate f ermentation systems that are capable of being stepped up to meet peak output when necessary. In the standard batch process, volumetric produ ctivities are controlled mainly by cyclic variations in growth and fer mentation rates and by the amount of yeast in suspension as a result o f the gas-lift action taking place in the fermentor. Thus, fermentor d esign must be optimized with respect to agitation and yeast concentrat ion. Reduced process times may be achieved in cylindroconical vessels because of increased movement within the fermentor. Unfortunately, hig h degrees of agitation have been shown to give flavor problems. The ad verse effects of agitation on beer quality may be prevented by operati ng under fed-batch conditions. Another approach to improve volumetric productivity is cell immobilization. With the successful application o f immobilized yeast reactors for continuous beer maturation, as well a s for the production of low-alcohol and nonalcoholic beers, one can ex pect an increasing contribution of immobilized yeast systems to the de velopment of a new process area in the brewing industry.