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Theses and Dissertations

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Browsing Theses and Dissertations by Author "Avens, Jack, committee member"

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    Influence of barley genetics on beer chemistry, flavor, and flavor stability
    (Colorado State University. Libraries, 2017) Bettenhausen, Harmonie M., author; Bunning, Marisa, advisor; Heuberger, Adam, advisor; Avens, Jack, committee member; Broeckling, Corey, committee member; Stone, Martha, committee member
    In the brewing industry, identifying superior ingredients that provide distinct flavors is an important area of research. While the contribution of raw ingredients such as yeast and hops to flavor is well understood, it is currently unclear if different genotypes of barley provide unique flavor to beer. In brewing, barley is malted to provide saccharides and enzymes for fermentation, however the malt also contains thousands of metabolites that may influence flavor. The goals of this study were to determine (i) if there would be metabolite differences among six commercial barley genotypes, (ii) if differences in barley chemistry are reflected in the chemistry of the beer, (iii) if the differences in the beer chemistry impact sensory attributes of beer, through flavor and flavor stability, and (iv) if there are barley and/or malt metabolites that can be markers for beer flavor and/or flavor stability. Six distinct malts were brewed into six beers using a recipe designed to evaluate differences in flavor. The malts were derived from the barley genotypes: Copeland, Expedition, Full Pint, Meredith, Metcalfe and PolarStar were grown and malted in either Canada or the U.S. Metabolomics was used to characterize chemical variation among the six malts and beers using RP-UHPLC-MS, HILIC-MS (non-volatile metabolites), HS/SPME-GC-MS (volatiles), and ICP-MS (metals). The metabolomics analysis detected 5,042 compounds in malt, and 217 were annotated as known metabolites and included amines (20 metabolites), amino acids (36), fatty acids/lipids (40), sugars (11), phenols (30), and others (80). A total of 4,568 compounds were detected in beer and included 246 annotated metabolites and included amines (9), amino acids (37), fatty acids/lipids/fatty acyls (28), sugars (10), phenols (20), esters (89), aldehydes (21), others (31). The chemical profiles of the six malts and beers were evaluated for metabolite variation using principal component analysis (PCA) and analysis of variance (ANOVA). Principal component analysis was conducted on the annotated metabolites and demonstrated that each of the six malts and beers contained unique chemical profiles. ANOVA characterized 150/217 malt metabolites (69.1%) and 150/246 beer metabolites (60.9%) varied among genotype (ANOVA, FDR adjusted p < 0.05). The six beers were evaluated for flavor using a modified Quantitative Descriptive Analysis® (QDA) for 45 sensory traits at 0, 4, and 8 weeks of storage at 13 °C. PCA characterized flavor differences among the six beers at 8 weeks and Full Pint was described as fruity and Meredith as corn chip. The metabolite and sensory data were integrated using two approaches: Spearman's correlation and two-way orthogonal projection to latent structures (O2PLS). The analyses revealed associations between fruity or corn chip flavor in beer with beer purines/pyrimidines, volatile ketones, amines, and phenolics; and malt lipids, saccharides, phenols, amines, and alkaloids. Taken together, these data support a role of barley metabolites in beer flavor and flavor stability. As a raw ingredient, malted barley genotypes should be evaluated for a contribution to flavor, and this may be a future target for plant breeding efforts to selectively improve flavor and flavor stability quality in beer.
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    ItemOpen Access
    Influence of roasted barley on quality of beer
    (Colorado State University. Libraries, 2013) Davis, Dave, author; Stone, Martha, advisor; Avens, Jack, committee member; DeVoe, Dale, committee member
    The research examined the influence of roasted barley content of beers on the quality of the resulting product. Recent researchers have indicated that moderate consumption can be a source of beer specific antioxidants, help reduce the risk of cardiovascular disease, and lower the occurrence of certain types of cancers. Beers were made with two-row malted and six-row unmalted roasted barley. Brews contained varying levels of the unmalted six-row roasted barley with the balance of the grain bill composed of two-row malted barley. They were analyzed for total phenolic content, sensory properties, and the physical properties specific gravity, color, and calculated alcohol. Four test groups were prepared with four replications of each test group for a total of 16 brews. No significant differences (P > 0.05) were found between the test brews for total phenolics. Total phenolics ranged from 314.77 to 451.72 micromoles / 100 milliliters for the test brews. Using Kuskal-Wallis one-way analysis of variance, a significant difference was found (χ2 =14.328, p = 0.00249) which demonstrated an increase in beer color as the percentage of roasted barley increased for the beer treatments. A significant difference was found in the organoleptic properties of the finished beers for total score, but not in individual categories. Perception of the bitter and burnt characteristics imparted by roasted barley appeared to increase as the percentage of roasted barley increased. This was not necessarily viewed as a detriment to the beer, but as an increase in complexity that added to the overall flavor and balance of the beer. There was a linear progression (P > 0.05) in the scores for aroma and appearance as the percentage of roasted barley increased. No significant differences (P > 0.05) were found in original or final specific gravity or within calculated alcohol values.