The impact of process parameters on flavour profile of alcohol-free beer from a single-stage continuous gas-lift reactor with immobilized yeast

Abstract

In order to study the formation and conversion of the most important flavour compounds, the real wort used in alcohol-free beer fermentation was mimicked by a complex model medium containing glucose, yeast extract and aldehydes (hexanal, 2-methyl propanal, 3-methyl butanal, furfural). Fermentation experiments were carried out in a continuously operating gaslift reactor with brewing yeast immobilized on spent grains. During continuous experiment, parameters such as oxygen supply, residence time (Rt) and temperature (T) were changed to find the optimal conditions for alcohol-free beer production. The formation of ethanol, higher alcohols (HA), esters (ES), reduction of aldehydes, and consumption of glucose were observed. The results suggest that the process parameters, particularly the oxygen supply, represent a powerful tool in controlling the degree of fermentation and flavour formation carried out by immobilized biocatalyst. Under optimal conditions in the continuous immobilized cell reactor it was possible obtain a fermented model medium with a composition approaching commercial alcohol-free beers.