Top pressure and temperature control the fusel alcohol/ester ratio through yeast growth in beer fermentation

Temperature and toy pressure are key factors for maintaining a consistent quality of lager beer Their influence on yeast growth, CO2 production, final concentrations of fusel alcohol and ester and production kinetics was analysed under industrial conditions. Fermentations of 12 degreesP lager wort were performed at 10 degreesC or 16 degreesC temperature and 1.05 bars or 1.8 bars top pressure, corresponding to dissolved carbon dioxide concentrations of 1.98 g/litre to 3.65 g/litre. Analysis of variance was performed to test the significance of temperature and dissolved CO2. Results show that temperature increases fermentation rate and the production ratio and final concentration of fusel alcohol, independently of the top pressure applied. Conversely, dissolved carbon dioxide controls the production rate and final concentration of ester by limiting yeast growth. Relationships between initial or maximum ester production rates and maximal growth rates were shown. Considering the metabolic pathways occurring during anaerobic growth of yeast, a limited production of acetyl CoA was expected in cultures with high concentrations of dissolved carbon dioxide. Also, final ester concentration and biomass produced are linearly correlated. Furthermore, whatever the ester considered, its synthesis is not influenced by corresponding fuse alcohol availability. It was demonstrated that fermentations performed with a reasoned combination of temperature and top pressure can result in a beer of distinctive aroma without resorting to modification of the initial wort or yeast strain.