Graduate Thesis Or Dissertation
 

The influence of polyphenols and humulinones on bitterness in dry-hopped beer

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  • This research sought to determine the origin of bitterness as a result of dry-hopping. An unhopped ale was dry-hopped and examined in the controlled dry-hop experiment and commercial beers were examined for chemical changes from dry-hopping in the commercially dry-hopped beer survey. This thesis work suggested specific bitter hop components that contribute to the bitterness of dry-hopped beer. The controlled dry-hopping experiment set out to determine specific sensory properties of dry-hopped beer. Using quantitative descriptive analysis, UV-spectroscopy, and liquid chromotography, the perceived bitterness intensity, aroma intensity, and hop component concentrations were determined. An unhopped ale (13° Plato Original Gravity, 2.53° Plato Final Gravity, 5.1 pH) was employed as the base and control for the study. Chinook pellets (13% alpha acids, 3.4% beta acids) were dry-hopped into the beer at 4g/L and 16g/L and examined after several exposure times: 6, 24, and 72 hours. Samples were then taken from each of the beers and analyzed for concentrations of hop acids, polyphenols, and Bitterness Units (BU). A trained sensory panel rated the samples for bitterness intensity and aroma intensity on two separate categorical scales (0-9) over 6 testing sessions. Chemical analysis indicated an increase in BU, polyphenols (mg/L), and humulinones (mg/L) from dry-hopping. The dry-hopped samples were also found to have significantly higher perceived bitterness intensity and aroma intensity compared to the unhopped control. Correlations between the quantitative data and the sensory data were determined. Overall, perceived bitterness intensity and aroma intensity for these dry-hopped samples could be predicted by polyphenols, humulinones, and the BU measurement. The commercially dry-hopped beer survey examined pre- and post-dry-hopped samples of commercial beers for chemical changes. The aim of this study was to determine the specific non-volatile hop compounds coming from dry-hopping. Commercial examples from breweries in the Pacific Northwest were examined for differences in BU, polyphenols, iso-alpha-acids (IAA), humulinones, hulupones, and alpha acids. Consistent with findings from the first study, polyphenols and humulinones increased as a result of dry-hopping. A notable finding indicated total IAA decreased with dry-hopping. Contributions to the BU measurement were predicted with multiple linear regressions, indicating humulinone concentrations as a major contributor to BU from dry-hopping. Further research is needed to determine predictions for the BU measurement using concentrations of IAA, humulinones, hulupones, and polyphenols. These studies indicate dry-hopping contributed bitterness to beers. The addition of humulinones, hulupones and polyphenols as a result of dry-hopping further suggested these compounds as the bittering components. With the knowledge of the bitter compounds added as a result of dry-hopped, the brewing industry can better understand the measured and perceived bitterness of their beers.
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file details ParkinEllenJ2015.pdf 2017-08-09 Pubblico Scaricare