, Suntory Liquors Limited, Osaka, Japan
ABSTRACT: Aroma characters derived from hops are very important for the quality of beer, as they can give an attractive sensory impact to beer by choosing suitable hop varieties, hop boiling conditions, fermentation conditions, and so on. In order to develop strategies to facilitate an attractive hop aroma in beer, we have been trying to clarify the relationship between hop aroma qualities in beer and brewing conditions. Many researchers have been studying hop aroma focused mainly on the essential oils in hop such as terpenoids. But these compounds are not necessary brought directly into beer products as they are. When they go through thermal reaction, oxidation, revelation from their glycosides, and biotransformation by yeast, there are chemical changes to different odor active compounds that are destined for final beer products. Such complexity makes the profiling of hop aroma in beer for mining the key compounds very difficult. In order to estimate the influencing compounds, the idea of "food metabolomics" was introduced for analyzing the data. Five hopped beers were brewed using different hop varieties, as well as unhopped beer. The aroma compounds were analyzed comprehensively by GCÃ—GC/TOF-MS, and sensory evaluation was also performed. Both results, chemical analysis and sensory data, were subjected to multivariate analysis to correlate chemical components and sensory evaluation. As a result, influencing compounds were distinguished from other numerous compounds. For suitable boiling conditions to give preferable hop aroma quality and intensity, linalool, a floral note component in beer, was used as one of the indicators for the hopped beer, because controlling the concentration of linalool in beer is essential for achieving target quality. In order to rationalize the factors that may affect the concentration of linalool during the boiling process, we have carried out brewing experiments using model solutions, as well as pilot scale brewing under various conditions, such as the timing of hop addition, temperature and amounts of late hopping, gravity of the wort, and so on. We also have focused on other hop aroma compounds, in addition to linalool, to explain the differences in organoleptic characteristics of beers. For the fermentation conditions, two different brewing yeast strains were used to examine the resulting hop aroma characteristics and hop derived components. Although the same cold wort was used for the fermentations, significant differences in hop aroma portraits were perceived. The obtained results, thus, are attributable to differences in metabolites generated from the components derived from hops by different yeasts. Further detailed investigations on the effects of hop on beer aroma, particularly on the changes during brewing, are awaited.
Takako Inui graduated from Kyusyu University. She started her research career with Suntory Ltd. in 1989 at the Institute for Fundamental Research. Since 2002, she has been conducting research at the Institute for Beer Development on the development of brewing technology and flavor science of beers, including hops.