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

Abstract

‘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. © 2018 The Institute of Brewing & Distilling

Assessment of Volatiles and Polyphenol Content, Physicochemical Parameters and Antioxidant Activity in Beers with Dotted Hawthorn (Crataegus punctata)

“…In a study about wines made from hawthorn fruit juice, conducted by Zhang et al [47], it was shown that concentration of ethyl hexanoate in wines was 7 times higher than in BJ, 10 times higher than in BC, and similar to the concentration in BF. Another ester identified in hawthorn fruit and all tested beers was ethyl (4E)-4-decenoate, which is characterised by fruit (pineapple), cognac and wax flavours [48,49]. It was detected in the tested samples in the amount of 0.1267 µg/100 mL for BJ, 0.4505 µg/100 mL for BF and 0.0985 µg/100 mL for BC.…”

Biotransformation of hop derived compounds by Brettanomyces yeast strains

“…Therefore, an understanding of the interaction of yeast with hop derived compounds is required. De novo synthesis of monoterpene alcohols in conventional brewer's yeast has also been reported, in both natural and genetically engineered strains (6,12).…”

“…Recently it has been reported that there can be synergistic effects on flavour formation between yeast and hops (3,4). The authors found that monoterpene alcohols from hops can be metabolised by brewer's yeast, imparting tropical and citrus flavours, however the exact mechanisms are not fully understood (3,5,6). It is not clear whether similar effects are catalysed by Brettanomyces species and an evaluation of this would aid in understanding the mechanisms behind the positive attributes of brewing with this yeast.…”

Changes in key hop‐derived compounds and their impact on perceived dry‐hop flavour in beers after storage at cold and ambient temperature

“…The evolution of key hop aroma compounds during storage at 20°C for 10 months was evaluated based on a selection of 15 hop compounds representing the major functional groups (esters, ketones, terpene alcohols, monoterpenes and sesquiterpenes) present in the essential oil. These compounds are presented in Table 4 alongside their aroma impression, and were selected because they have been identified in several studies to contribute in some form to the overall flavour of dry-hopped beers (2,6,8,9,24,25).…”

“…Hops are the major source of bitterness and aroma in beer and are loosely categorised as 'bittering' , 'dual purpose' and 'aroma' varieties. Bitterness varieties are selected primarily for their bittering potential whilst 'dual purpose' hop varieties, which contain appreciable levels of both α-acids and essential oil can be applied in the brewhouse interchangeably to derive both bitterness and aroma in beer (1,2). Aroma varieties are often used to produce sensorially complex beers and are selected based on the amount and constituents of essential oil ranging from 0.5 -4% w/w of hop cones (3).…”