66. Hop oil extracts add more to beer than hop aroma! Investigating the impact of hop essential oils on bitterness perception

Olayide Oladokun (1), David Cook (1), Joanne Hort (1), Sue James (2), Katherine Smart (2); (1) University of Nottingham, Loughborugh, U.K.; (2) SABMiller plc, U.K.

Technical Session 19: Beer Bitterness
Wednesday, August 17  •  8:15–9:30 a.m.
Tower Building, Second Level, Grand Ballroom

Bitterness and hop aroma are two important flavor attributes driving consumer acceptance of beer and are derived from the addition of hops and hop products during the brewing process. While bitterness is achieved by the thermal isomerization of alpha-acids to bitter tasting iso-alpha-acids, volatile aroma compounds within the essential oil fraction of hops contribute significantly to beer flavor and “hoppy” characters. To achieve desirable “hoppy” flavor in beers, brewers can add aroma hops at several points during the brewing process, e.g., late in the wort boil, or during fermentation or maturation (dry-hopping). Purified hop products such as hop oils are also commercially available and could be added throughout the brewing process for flavor intensification and differentiation of products. It has previously been reported that the addition of certain hop oil fractions to unhopped beer can elicit an increased bitterness perception (Goiris et al., J. Inst. Brew. 108(1):86-93, 2002), but the mechanisms for this remain unknown. In this study an unhopped base beer was manufactured from 70% pilsner malt and 30% dextrose adjunct, to which a liquid iso-alpha-acid extract (Isohop, 30% wt/wt) was added to achieve low, medium and high bitterness levels, corresponding to a bitterness concentration of 13, 25 and 42 mg/L, respectively. Hop oil products representing the total essential oil constituents of Hersbrucker and East Kent Goldings (EKG) hop varieties were added at three levels (0, 0.4, 0.8 µL/mL). Perceived bitterness intensity and bitterness character were assessed by a trained panel at each bitterness level with and without nose clips. The use of nose clips enabled the olfactory aspect to be decoupled from taste and mouthfeel aspects of bitterness perception. Beer samples were evaluated for perceived bitterness intensity, harshness, roundedness and linger using a rank-rating approach. The impact of the different aroma levels at each bitterness level was determined using ANOVA. The results showed that aroma compounds within hop oils significantly affected bitterness perception depending on bitterness level and hop variety. At low bitterness (13 mg/L), beers with Hersbrucker hop oil added were perceived as more bitter and of rounded bitterness character relative to beers without hop oils. The use of nose clips eliminated this observation, implying that the presence of congruent hop aromas results in a perceptual taste-aroma interaction—not only adding hop aroma but also increasing perceived bitterness. Conversely, at high bitterness levels (42 mg/L), even when nose clips were used, beers with Hersbrucker hop oil added were still perceived as more bitter and of harsh bitterness character. At high bitterness levels, these increases in perception with nose clips point toward the hop oil extract stimulating other receptors, e.g., trigeminal receptors, which in tandem with the high bitterness cause perceptual interactions enhancing bitterness intensity and also affecting bitterness character. Some differences in bitterness characters were also observed with the EKG oil extract. Our findings represent a significant step forward in terms of understanding perceived bitterness flavor in beer and the wider impact of hop compounds on sensory perception.

 Olayide Oladokun received an M.Chem. (Hons.) degree in chemistry with industrial experience from the University of Manchester in 2011 before joining the Brewing Science Department of the University of Nottingham as a research technician later that year. In 2014, he completed an M.Res. research project primarily focused on the analysis of hop bitter acids in beer. Olayide is now in the final year of his Ph.D. studies (sponsored by SABMiller and the University of Nottingham) investigating the “Quality of Bitterness” in beers. His hobbies include home brewing and sports.