KIYOSHI TAKOI (1), Yutaka Itoga (2), Koichiro Koie (2), Yuuta
Katayama (1), Masayuki Shimase (1), Takayuki Kosugi (1), Yasuyuki
Nakayama (1), Junji Watari (1)
(1) Sapporo Breweries Ltd., Yaizu, Shizuoka, Japan; (2) Sapporo Breweries Ltd., Sorachi-gun, Hokkaido, Japan
Various beers contain many flavor compounds derived from barley
malts, hops, and yeast fermentation. Among these flavor compounds,
terpenoids are mainly derived from hops. Especially, linalool, one of
the monoterpene alcohols, has been regarded as an important factor for a
hop-derived beer flavor. In this report, we focus on contributions of
other monoterpene alcohols (geraniol, β-citronellol, nerol, and
α-terpineol) to hopped beer flavor. Several researchers have reported
that monoterpene alcohols are biotransformed by brewing yeasts during
beer fermentation, and that geraniol is mainly transformed to
β-citronellol. First, we investigated biotransformation of monoterpene
alcohols during fermentation of hopped beer by using various hop
varieties. As a result, geraniol drastically decreased during the first 3
days. β-Citronellol was almost absent in wort and gently increased
during total fermentation period. The concentrations of geraniol and
β-citronellol in finished beer increased depending on the initial
concentration of geraniol in wort. We next examined flavor
characteristics of monoterpene alcohols and found that there was an
additive effect among linalool, geraniol, and β-citronellol. The
test-brewed beer containing these three monoterpene alcohols had a
citrus flavor. Therefore, we carried out the screening of various hop
varieties and selected Citra as a geraniol-rich hop. The use of Citra
was effective for enriching the concentration of geraniol and
β-citronellol in the finished beers and this Citra beer had a strong
citrus flavor. We evaluated the synergy of geraniol and β-citronellol
under coexistence with excess linalool, simulating the composition of
the three monoterpene alcohols in the Citra beer, and found that the
flavor impression became lime-like citrus by coexistence of all three
monoterpene alcohols. From these results, it was suggested that geraniol
metabolism by brewing yeasts contribute to the citrus flavor of beer.
In addition, the variation on geraniol contents among the U.S. hop
varieties is also discussed.
Kiyoshi Takoi graduated from Tohoku University with an M.S. degree in
agricultural chemistry in 1989 and joined the Brewing Research
Laboratories of Sapporo Breweries, Ltd. as a biochemist. From 1989 to
2002, he worked on brewing chemistry and mainly investigated beer foam
stability. During 2002–2005, he evaluated the brewing properties of
malts and hops using the pilot malting and brewing plants in the
Production & Technology Development Center. In 2006, he managed
product development in the New Product Development Center. During
2007–2008, he worked in the Frontier Laboratories of Value Creation as a
lead research brewer and mainly investigated hop-derived flavor
compounds. At present, he is working in the Value Creation Department of
Sapporo and developing new products. He received a Ph.D. in
agricultural chemistry from Tohoku University in 2011.
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