PITCHING RATES RELATED TO GLUCOSE AND FRUCTOSE UTILIZATION INSaccharomyces cerevisiae

Pitching rates, in the range 1.5 g/litre to 24 g/litre of yeast in high gravity sucrose adjunct laboratory-scale wort fermentations, are directly proportional to the natural logarithm of glucose utilization throughout fermentation, whereas this relationship only holds for fructose utilization during the intermediate phases. The natural logarithmic rate of fructose utilization in the latter stages of fermentation remains constant irrespective of the pitching rate used. Adjustment of the pitching rate allows residual fructose concentrations at the end of fermentation to be regulated such that they remain below the fructose taste threshold in beer. The difference in utilization rates produced by the preferential utilization of glucose over fructose appears to remain constant irrespective of the pitching rate used. This differential may be ascribed to the competitive inhibition of fructose transport by glucose for their common hexose constitutive facilitated diffusion membrane transport system in S. cerevisiae.