The influence of brewing yeast strains on monoterpene alcohols and esters contributing to the citrus flavour of beer

'Aroma hops' and especially newly bred 'flavour hops' are used throughout the world to impart citrus-like and/or exotic fruit-like flavours to craft beers. Citrus-like flavours in beer are known to be influenced by yeast fermentation when transforming certain secondary metabolites of the hops such as monoterpene alcohols. In this study, the influence of different Saccharomyces cerevisiae/pastorianus brewing yeast strains on the citrus flavour of beers hopped at different times during beer production (30 min boiling, added during fermentation, added during maturation) with Hersbrucker, Mandarina Bavaria or Hallertauer Magnum was investigated. Yeast strains TUM 68, TUM 506, TUM 511, TUM 34/70, TUM 69 and TUM 193 that are widespread in worldwide beer production were used for standardised laboratory scale fermentations. The yeast strains showed similarly low glucoside hydrolase activity in fermenting beer. The de novo synthesis of monoterpene alcohols was identified, and the geraniol decrease during fermentation was confirmed using HS-GC-MS. This research indicates that the impact of monoterpene alcohols on the citrus flavour of beer could be significantly influenced by flavour active esters owing to the combinatory effects of the flavouring substances. The results of instrumental analysis and sensory evaluation suggest that the choice of yeast strain is significant for the intensity of citrus flavour in beer. (C) 2018 The Institute of Brewing & Distilling