Influence of fermentation compounds from yeast on the quality of hop aroma

Technical Session 01: Hops I Session
Hitoshi Takemura, Kirin Brewery Company, Limited

ABSTRACT: Hop aroma is a very important factor that contributes to the flavor of beer; therefore, a great deal of care is taken to adjust hop aroma by controlling brewing parameters. Nevertheless, even when using the same hop variety under the same conditions (timing of addition and quantity), samples can have different aroma intensities if fermentation is performed using different brewing conditions (temperature, yeast pitching rate, etc.). Therefore, we investigated the cause of differences in aroma intensities in order to facilitate more precise control of hop aroma. We had the following two hypotheses: “the extent of conversion of hop aroma by yeast varies according to the brewing conditions” (hypothesis 1), and “hop aroma is masked by compounds that are produced by yeast during fermentation” (hypothesis 2). To test these hypotheses, samples that had different intensities of fruity aroma (lychee, citrus-like), even though the same hop variety (American Cascade and New Zealand Motueka) and hop addition conditions were used, were subjected to GC/MS analysis to determine whether there were any differences in the quantity of aroma compounds. The results indicated that the amount of linalool and the amount of beta-citronellol produced by the yeast did not significantly differ between the samples. This suggests that the validity of hypothesis 1 is low. Furthermore, as there was a difference in the amount of compounds that arise from fermentation, hypothesis 2 appears to be valid. Next, we investigated the influence of esters and alcohols on hop aroma. We observed a tendency for alcohols (e.g., 1-heptanol) to mask fruity aromas. Therefore, we brewed samples in which cold wort from the same batch was fermented (in a 20 L scale fermentor) using different fermentation conditions. Sensory evaluations revealed differences in fruity aroma between samples. Statistical analysis indicated that there was a significant negative correlation between 1-heptanol and fruity aroma. Furthermore, 1-heptanol was positively correlated with the number of yeast cells added at the start of fermentation and fermentation temperature. These results further support hypothesis 2 and suggest that it is important to control fermentation conditions. The results of this research have lead to the establishment of specific brewing conditions for more precise control of hop aroma.

Hitoshi Takemura has worked for Kirin Brewery Company Limited since receiving a master’s degree in life science from Kyoto University in 2002. He worked in the Quality Assurance Department of the Tochigi brewery for three years and then entered the Laboratory for Brewing, where he conducted research on the use of hops in wort boiling. From 2008 to 2010 he worked as a guest researcher in Lehrstuhl fuer Brau- und Getraenke Technologie fuer Technische Universitaet Muenchen. Since August 2010 he has worked in the Brewing Technology Development Center.