Control of Hop Aroma Impression of Beer with Blend-Hopping using Geraniol-rich Hop and New Hypothesis of Synergy among Hop-derived Flavour Compounds

In previous studies, we found that the concentration of geraniol and beta-citronellol in finished beer could be enriched depending on the initial geraniol content in the wort, as a result of single-hopped test-brewing by using geraniol-rich hop. In this study, we tried to confirm the effect of blend-hopping using geraniol-rich Bravo hop on the concentration of monoterpene alcohols during fermentation. As a result, the additional Bravo hop, at only 0.4 g of hop/L dosage, could increase approx. 20 mu g/L of geraniol and > 15 mu g/L of beta-citronellol in blend-hopped beers in comparison with single-hopped control beers. We have also previously demonstrated that the coexistence of linalool, geraniol, and beta-citronellol could increase the average scores of 'Citrus' by using the model solution (5 % v/v ethanol, carbonated). In this study, we observed same effect of increase of monoterpene alcohols on the change of flavour characters, first time in hopped beers. Furthermore, we found that there might be an additive effect between a volatile thiol (4-methyl-4-sulfanylpentan-2-one (4MSP)) and monoterpene alcohols (linalool and geraniol) and that only 1.2 ng/L of 4MSP was enough for this effect. In addition, as a result of model sensory evaluation, it was also found that the 'Tropical' character could be maximized under coexistence of 4MSP and three monoterpene alcohols (linalool, geraniol, and beta-citronellol). We assumed that the synergy among volatile thiols and monoterpene alcohols could contribute to such flavours in beers made from certain 'Flavour Hop' varieties, containing both groups of compounds. This result is also useful for determining blend-hopping recipe based on a composition of flavour compounds of each hop variety.