O-10. Investigation for improving metallic flavor in third-category beer

Presenter: Shinichiro Yamamura, Suntory Liquors Limited, Ohra-gun, Gunma, Japan

“Metallic flavor” is a metal-like flavor that gives the impression of rusty iron or of a can. This flavor is easy to detect in beers with a light taste, such as third-category beers, and it is a factor that negatively impacts beer quality. Third-category beers have been rapidly expanding in the Japanese beer market, and the ratio of sales is about 35%. Therefore, it is an urgent task for us to improve metallic flavor. Based on a previous study, it was known that the substances causing metallic flavor are 1,5-octadien-3-ol and its oxide 1,5-octadien-3- one, which are oxides from an unsaturated fatty acid derived from raw materials. Our attempts to reduce metallic flavor could not proceed, however, because we did not know how the substances are generated. We analyzed a product that was judged as having a strong metallic flavor in our sensory evaluation. It was confirmed that this product had a high iron concentration in the beer. Based on this fact, we performed an iron addition experiment to elucidate the mechanism generating the metallic flavor. From this, we developed the hypothesis that it is necessary to reduce the unsaturated fatty acid and iron concentrations in the beer to improve metallic flavor. We tried to reduce wort turbidity during the lautering process to decrease the unsaturated fatty acid, because it had already been reported that there is a correlation between wort turbidity and the concentration of the unsaturated fatty acid (Kühbeck et al., J. Inst. Brew. 112:222-231, 2006). We also tried to reduce the amount of kieselguhr to decrease the iron concentration, because kieselguhr includes some iron. As a result, we were able to reduce the substances causing the metallic flavor and to improve the sensory evaluation score dramatically. We also carried out a sensory evaluation after eating various foods and consuming beers with high and low iron concentrations. When there were high concentrations of iron, a metallic flavor could be detected in reaction to the unsaturated fatty acid derived from the food. From this result, we could prove our metallic flavor hypothesis.

Shinichiro Yamamura is an assistant brewmaster in the Suntory Tonegawa brewery. The main subject of his work is development of brewing technology. He majored in molecular biotechnology at Hiroshima University, and he was engaged in elucidation of molecular mechanisms of mouse olfactory. He joined Suntory Ltd. in 2010. He is now engaged in improving beer quality and development of brewing technology.

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