196. Elucidation of the ester formation mechanism in top-fermenting yeast

Chie Hayashi (1); (1) Suntory Beer Limited, Osaka, Japan

Yeast, Fermentation, and Microbiology

We developed a weizen beer with both a “refreshing finish” and overwhelming “banana-like sweet and fruity aroma.” Iso-amylacetate is a cause of the banana-like sweet and fruity aroma, and its normal concentration in weizen beer is said to be 2.5-3.5 ppm. To achieve the overwhelming banana-like sweet and fruity aroma, we thought that a much higher concentration of iso-amylacetate is required. Therefore, we were challenged to elucidate the mechanisms of ester formation during beer production process, in order to regulate iso-amylacetate concentration in the final beer. According to previous research, iso-amylacetate is synthesized from acetyl-CoA and iso-amylalcohol catalyzed by alcohol acetyl transferase (AATase) in yeast. The formation of iso-amylacetate is influenced by various factors, such as wort composition, including unsaturated fatty acids, amino acids and fermentation conditions. The purpose of this study is to elucidate the effect of the following factors on iso-amylacetate production during mashing and fermentation. The effects of substrate (of precursor) concentration, fermentation temperature, and aeration rate were investigated by a 2 L scale fermentation test. Substrate concentration in wort, such as valine or leucine, is more effective than fermentation conditions in the range of investigated conditions. Detailed results will be reported at the conference. Based on the results obtained by the 2 L scale test, we designed the brewing conditions to produce a beer with a higher concentration of iso-amylacetate at a 50 hL scale and confirmed the effectiveness of various factors investigated. Through this study, we obtained the technology to improve the banana-like sweet and fruity aroma in top-fermenting yeast by controlling certain brewing conditions.

Chie Hayashi studied biotechnology at Kyoto University and got her master’s degree in 2014. Following graduation, she join Suntory Beer Ltd. Her research area is brewing technology.