Kuniyasu Tamaoka, Suntory Beer Limited, Gumma,
Yeast, Fermentation, and Microbiology
Monoterpene alcohols, such as linalool and geraniol, are important natural flavor compounds that are contained in beer via hopping. It is known that the metabolism of a monoterpene alcohol is influenced by the yeast strain. However, no one has clarified the behavior of monoterpene alcohols in fermentation. So we investigated the behavior of monoterpene alcohols in fermentation and the relationship between monoterpene alcohols' metabolism and the fermentation parameter in the commercial plant. First, we investigated the behavior of monoterpene alcohols (geraniol, linalool, nerol, α-terpineol, geranyl acetate, citronellyl acetate, and β-citronellol) in fermentation and lagering every day for 14 days by using lager yeast. A big change of monoterpene alcohols occurred for the first 48 hours, and only a little change followed it up to 14 days. Geraniol especially was observed to decrease rapidly in the first 3 hours and then to decrease slowly up to 48 hours. This result indicates there is a close relationship between monoterpene alcohols' metabolism and the growth of yeast. Second, we carried out several tests that had different fermentation temperatures (12.5 ℃, 13.5 ℃, and 14.5 ℃) to investigate the effect of temperature on monoterpene alcohols' metabolism. We found that a high fermentation temperature, which led to high growth in yeast, was influenced by lower content of geraniol and by higher content of the other six monoterpene alcohols. It is suggested that geraniol content in beer became higher with lower growth of yeast and the six other monoterpene alcohols' content in beer became higher with higher growth of yeast. Finally, we also investigated the relationship between monoterpene alcohols' metabolism and DCO2. Higher DCO2 caused lower content for all seven monoterpene alcohols, including geraniol. It was suggested that monoterpene alcohol content in beer became higher with lower DCO2.
Kuniyasu Tamaoka graduated from the Graduate School of Information Science and Technology at Osaka University. He joined Suntory Holdings Ltd. in April 2011 and started his career in the brewing department. His work is beer product management in Tonegawa Brewery.