The Effects of Wort Valine Concentration on the Total Diacetyl Profile and Levels Late in Batch Fermentations with Brewing Yeast Saccharomyces Carlsbergensis

Abstract

Total diacetyl concentration often is used by the brewing industry to determine the time when fermentation or maturation is complete. As a result, fermenter or maturation vessel productivity often is dictated by total diacetyl concentration. Lab-scale batch fermentations using brewing yeast were carried out on wort containing different concentrations of free amino nitrogen (FAN). The resulting valine concentrations of these worts varied from 83 to 211 mg/L without altering the amino acid distribution. As the initial wort FAN and valine concentrations decreased, the rate of valine uptake increased, coinciding with lower final valine concentrations. Experiments using wort with initial valine concentrations of 130–140 mg/L showed the highest diacetyl levels late in fermentation. At more extreme shortages of valine (83–115 mg/L), a diacetyl double peak also occurred; however, the second peak occurred early enough in the fermentation that the yeast were able to reduce diacetyl to acceptable levels. Valine concentrations of 130–140 mg/L were found to be just below the critical concentration necessary for single-peak diacetyl profiles. The implications of these findings are greatest for breweries fermenting worts with valine concentrations just above the critical value for their set of fermentation conditions.