Norio Doi (1), Masayuki Aizawa (1), Minoru Kobayashi (1), Susumu Masuda (1); (1) Asahi Breweries Ltd., Ibaraki, Japan
The perceived quality of beer is predominantly influenced by flavor. One of the most important and undesirable flavors associated with beer is metallic taste, as even trace amounts of metallic flavor impart a certain degree of unpleasantness. During the last ASBC Annual Meeting, we described the identification of the main compound associated with the metallic flavor of beer: 1-octen-3-one. In addition, it was determined that 1,5-octadien-3-one is the primary compound responsible for metallic flavor when beer is consumed together with seafood. As beer is often enjoyed with food, the reaction of components in beer with those in food to form compounds that impart a metallic flavor is of particular concern. Because the detection threshold of 1,5-octadien-3-one is only several parts per trillion, the formation of 1,5-octadien-3-one must be tightly controlled. Further study revealed that 1,5-octadien-3-one is formed when omega-3 long-chain fatty acids from seafood react with the iron present in beer. In addition, the formation of 1,5-octadien-3-one was shown to be highly related to iron concentration. Because the iron in beer is mainly supplied from iron oxides present in the kieselguhr used in the filtration process, we speculated that the formation of 1,5-octadien-3-one could be lowered by reducing the elution of iron from kieselguhr. To this end, we modified the filtration process, such as changing the kind of kieselguhr, and demonstrated that the formation of 1,5-octadien-3-one was reduced. Then, we could achieve the reduction of 1,5-octadien-3-one formation when we enjoyed beer and seafood by reducing the iron in the beer.
Norio Doi has been a researcher in the Research & Development Laboratories for Brewing at Asahi Breweries Ltd. since 2009. In 2009, he received his M.Eng. degree in polymer chemistry from Kyoto University, where he focused on tissue engineering.