Pilot-scale brewing using self-cloning bottom-fermenting yeast with highSSU1expression

Abstract

A pilot-scale fermentation was performed using SSU1-overexpressing bottom-fermenting yeast strains constructed by ‘self-cloning’. In these strains, the gene SSU1, encoding a plasma membrane protein that excretes sulphite, was highly expressed. The rate of fermentation of the two SSU1-overexpressing strains tested showed some reduction during the mid-fermentation phase as compared with the parental strain. These differences, however, did not affect overall fermentation and the final apparent extracts had decreased to a level normally obtained during brewing. The concentration of hydrogen sulphide in the wort remained low during fermentation in the case of the two self-cloning strains compared with the parent. The concentration of 2-mercapto-3-methyl-1-butanol, a sulphur compound that causes an ‘onion-like’ off-flavour, was also reduced in the case of the self-cloning strains, a result confirmed by sensory evaluation of the beer immediately after bottling. Furthermore, with these strains the anti-oxidation potential of bottled beer, as measured by electron spin resonance, was improved and the concentration of trans-2-nonenal in bottled beer after 7 days of accelerated aging at 37°C was decreased. These observations, together with the lower stale flavour score determined by sensory evaluation of bottled beer after a month of aging at 25°C, indicated that the flavour stability of the beer had been successfully improved. Copyright © 2013 The Institute of Brewing & Distilling