| Summary: | One of the most important contributions to flavour compounds in beer is that associated with the activity of yeast. A kinetic model that quantitatively predicts the influence of changing process parameters on yeast metabolism and the production of flavour compounds would be invaluable. However a review of the literature has revealed that there is an absence of good quantitative data on which to build a model. The literature uses a wide variety of yeast strains and undefined fermentation media. There is also very little quantitative analysis of flavour formation and the models that have been published have little physiological relevance. The aim of the present study was to develop a kinetic model that would describe the production of the higher alcohols, isoamylalcohol and isobutanol, by the yeast N.C.Y.C 1681 within a brewery fermentation system. H.P.L.C., G.C. and enzyme assay analytical methods were developed that allowed the determination of concentrations of pertinent medium components during a fermentation. Amino acid concentrations were determined using Pico-tag (P.I.T.C.) pre-column derivatisation chemistry. Beer volatile components were analysed using G.C. head space analytical procedures. Yeast growth was studied in experimental defined media and in the complex wort medium. The vessels of the study were stirred tank fermenters, tall tubes and brewery cylindroconicals. Higher alcohol production is intimately linked with the yeast populations amino acid metabolism. Thus the influence of medium nitrogen content was investigated in relation to catabolic and anabolic production of higher alcohols.
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