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​O-4. Behavior of hydrogen sulfide during late-stage fermentation

Presenter: Yutaka Yamaguchi, Suntory Liquors Limited, Japan. Coauthor(s): Taichi Maruhashi, Takuya Hashimoto, Kaneo Oka, and Nobuyuki Fukui, Suntory Liquors Limited, Japan.

Hydrogen sulfide gives beer an unpleasant off-flavor reminiscent of the smell of rotten eggs, so it is important to keep the concentration of hydrogen sulfide in finished beer well below the sensory threshold. Control of hydrogen sulfide at the end of fermentation is important not only for high quality beer, but also to keep the brewing period short. Hydrogen sulfide behavior during fermentation has been investigated. It is released from yeast cells during the cell maturation cycle and assimilated during the budding cycle. The decrease in beer’s hydrogen sulfide content during late-stage fermentation is attributed both to the purging effect of carbon dioxide and assimilation by yeast. Several reports have been published on the effects of fermentation conditions and gene modifications on the production of hydrogen sulfide. In this study, another behavior of hydrogen sulfide was observed in the late stage of fermentation at the low malt ratio wort. Although hydrogen sulfide levels in late-stage fermentation are normally low under our brewing conditions, under certain conditions hydrogen sulfide content remains high. It was suggested that yeast metabolism and the free amino acid concentration in the wort were key determining factors. After that stage, the hydrogen sulfide content increased again and then it declined at the end of fermentation. It seems that the hydrogen sulfide content is the result of the balance between its production, its assimilation, and the carbon dioxide purging effect. This investigation confirmed earlier work and provided a more detailed description of the behavior of hydrogen sulfide during the late stage of fermentation.

Yutaka Yamaguchi graduated with a master of the department of chemical science and engineering degree from Kobe University in 2005. After joining Suntory, he worked for two years in the position of second brewmaster at the Suntory Tonegawa Brewery in Gumma, Japan. Since 2007, he has been working at the Beer Development Department of Suntory Liquors Limited.