THE EFFECT OF LOW CO2PRESSURES ON THE ABSORPTION OF AMINO ACIDS AND PRODUCTION OF FLAVOUR-ACTIVE VOLATILES BY YEAST

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Abstract
Laboratory fermentation of 51 batches of wort under CO2 pressures of 0·5 and 1·0 atm have shown that whilst the speed of fermentation was affected only slightly, absorption of amino acids, production of several flavour-active compounds and some yeast features were affected. The CO2 pressure led to reduced absorption of Group B amino acids although Group A compounds were unaffected; fusel oil and ester concentration was reduced whereas that of the vicinal diketones and acetaldehyde was increased. Yeast crop and cell viability fell with increase in pressure and at 1·0 atm the mean cell volume was increased. The results suggest that CO2 could have significant effects on yeast and beer quality within the range of concentration which can be expected to occur in unpressurized commercial fermentations.