Biotransformation of Hop-Derived Monoterpene Alcohols by Lager Yeast and Their Contribution to the Flavor of Hopped Beer

Abstract

It is well-known that various beers contain many flavor compounds derived from barley malts, hops, yeast fermentation, and other raw materials. Among these flavor compounds, terpenoids are mainly derived from hops. Linalool, one of the monoterpene alcohols, has been found in various beers and been regarded as an important factor for a hop-derived beer flavor. We focus on contributions of other monoterpene alcohols (geraniol, beta-citronellol, nerol, and alpha-terpineol) to hopped beer flavor. Several researchers have reported that monoterpene alcohols are biotransformed by yeast and that geraniol is mainly transformed to beta-citronellol during the first 2-4 days in model fermentation. In this study, we investigated the biotransformation of monoterpene alcohols during fermentation of hopped beer by using various hop cultivars. As a result, geraniol drastically decreased during the first 3 days. beta-Citronellol was almost absent in wort and gently increased during the total fermentation period. The concentrations of geraniol and beta-citronellol in finished beer increased, depending on the initial concentration of geraniol in the wort. The continuous increase of beta-citronellol did not correspond to the fast decrease of geraniol. This increase of beta-citronellol might be partly explained by an occurrence of glycosidically bound flavor precursor and a glucoside hydrolase activity secreted from lager yeast. In addition, we examined flavor characteristics of monoterpene alcohols and found that there was an additive effect among linalool, geraniol, and beta-citronellol and that only 5 microg/L of geraniol and beta-citronellol were enough for this effect. Therefore, it is suggested that not only linalool but also geraniol and beta-citronellol might contribute to hopped beer flavor at lower levels, at which OAVs of these compounds become below 1.0.

Evaluation of Beer Fermentation with a Novel Yeast Williopsis saturnus

“…S. cerevisiae is able to convert the odourless linalyl glycoside to linalool via the action of β-glucosidases (38). Yeast has been shown to be able to convert geraniol to linalool (37,39), although geraniol was not detected in the wort.…”

The Contribution of Geraniol Metabolism to the Citrus Flavour of Beer: Synergy of Geraniol and β-Citronellol Under Coexistence with Excess Linalool

“…It had already been reported that the content of geraniol and β-citronellol in finished beer could be increased by enriching the initial geraniol content in the wort 27 . In beer production, hops (Humulus lupulus L.) are the main source of geraniol.…”

“…The flavour characteristics of monoterpene alcohols have also been reported 27 . Table I lists the olfactory descriptions of monoterpene alcohols and their group thresholds as determined by the sensory panellists.…”

“…It was assumed that geraniol and β-citronellol might contribute to the citrus flavour of these beers. This laboratory has previously published that there is an additive effect with linalool, geraniol and β-citronellol, and that this effect might contribute to the citrus flavour of hopped beer 27 . However, in the Citra beer and in the coriander beer, the content of the linalool was in excess in comparison with geraniol and β-citronellol ( Fig.…”

“…This laboratory has previously reported on the biotransformation of monoterpene alcohols during the fermentation of hopped beer using various hop cultivars 27 . Geraniol was observed to decrease during the first 3 days.…”