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

Temperature and toy pressure are key factors for maintaining a consistent q uality of lager beer Their influence on yeast growth, CO2 production, final concentrations of fusel alcohol and ester and production kinetics was anal ysed under industrial conditions. Fermentations of 12 degreesP lager wort w ere performed at 10 degreesC or 16 degreesC temperature and 1.05 bars or 1. 8 bars top pressure, corresponding to dissolved carbon dioxide concentratio ns of 1.98 g/litre to 3.65 g/litre. Analysis of variance was performed to t est the significance of temperature and dissolved CO2. Results show that te mperature increases fermentation rate and the production ratio and final co ncentration of fusel alcohol, independently of the top pressure applied. Co nversely, dissolved carbon dioxide controls the production rate and final c oncentration of ester by limiting yeast growth. Relationships between initi al or maximum ester production rates and maximal growth rates were shown. C onsidering the metabolic pathways occurring during anaerobic growth of yeas t, a limited production of acetyl CoA was expected in cultures with high co ncentrations of dissolved carbon dioxide. Also, final ester concentration a nd biomass produced are linearly correlated. Furthermore, whatever the este r considered, its synthesis is not influenced by corresponding fuse alcohol availability. It was demonstrated that fermentations performed with a reasoned combinatio n of temperature and top pressure can result in a beer of distinctive aroma without resorting to modification of the initial wort or yeast strain.