Factors influencing ethanol production rates at high-gravity brewing

The aim of this work was to investigate the influences of different fermentation factors on ethanol production rates by Saccharomyces cerevisiae (lager strain), at high-gravity brewing using response surface methodology. An empirical linear polynomial model was developed to describe the behaviour of the dependent variable as a function of significant factors. The resultant functional relationship in terms of coded values for predicting ethanol production rates was: Y=0.421+0.155X₂+0.0575X₂X_3, where Y represents the ethanol production rate (g/lh), and X₂ and X₃ are coded levels for fermentation temperature and nutrient supplementation, respectively. Patterns of yeast growth, decrease in wort gravity and ethanol production were also evaluated at the maximum ethanol production rate (0.694 g/lh). It was concluded that higher ethanol production rates could be achieved by increasing fermentation temperature and supplementing high-gravity worts with yeast extract, ergosterol and Tween 80.