Screening of Geraniol-Rich Flavor Hop and Interesting Behavior of β-Citronellol during Fermentation under Various Hop-Addition Timings

Abstract

In a previous study, we have focused on biotransformation of hop-derived monoterpene alcohols (linalool, geraniol, β-citronellol, nerol, and α-terpineol) and their contribution to the flavor of hopped beer. Geraniol showed a drastic decrease during the growth phase and a part of geraniol was converted to β-citronellol by yeast. β-Citronellol was almost absent in hop and wort and gradually increased during the total fermentation period. The concentrations of geraniol and β-citronellol in finished beer could be enriched depending on the initial geraniol content in the wort by using a geraniol-rich hop. As a result of sensory evaluation, there was an additive effect among linalool, geraniol, and β-citronellol, and the flavor impression became lime-like by coexistence of these three monoterpene alcohols. In this study, we compared the composition of monoterpene alcohols in various hops, including new flavor hop varieties. Of all screened hops, most of the U.S. hop varieties contained relatively large amount of geraniol. Cascade, Bravo, and Mosaic were screened as geraniol-rich flavor hops. By using these varieties, we brewed test beers under various hop-addition timings to compare the composition of three monoterpene alcohols and total hop flavor profiles in the finished beers. As a result, the content of geraniol in finished beer could increase by delaying the timing of hop addition, while the yeast growth phase was avoided. On the other hand, the β-citronellol contents in the finished beers made with the same hop variety (except Bravo) were present at almost the same levels, regardless of the timings of the hop addition, because of active generation of β-citronellol during the storage period. In addition, interesting behaviors of monoterpene alcohols, especially β-citronellol, observed in this study, and the relationship between the timing of hop addition and the profile of various flavor compounds in beer are discussed.