Graduate Thesis Or Dissertation
 

The Role of Alcohol Content on Sensory Aroma Detection Thresholds in Beer

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/p2676x83s

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  • This work set out to examine whether ethanol content can influence the human detection of volatile hop compounds in beer. Advances in chromatography have identified hundreds of chemical compounds in the essential oil of hops but only a fraction are directly associated with "hoppy" aroma. To screen compounds, sensory detection thresholds (the minimal concentration of a stimulus that can be detected by humans) are used to determine odor potency of aromatic compounds in a food system. Compounds present in concentrations multiple times above threshold will have a greater probability of contributing to the overall aroma than compounds that occur at concentrations much lower than their thresholds. One measure of flavor potency, odor activity value (OAV) is the concentration of an individual compound found in a food system divided by its sensory threshold concentration. The accuracy of the value is partially determined by the robustness of the threshold measurement, influenced by various psychophysical and chemical factors. Differences in individual perception, sensory testing methodology and flavor interactions contribute to the wide variation found in published threshold values. In addition to sensory factors, the chemical properties of flavor compounds determine the likelihood that the compound will be released from the matrix into the headspace of the container. The matrix (air, water, beer) in which the compounds are tested will impact the measured threshold value. For instance, published thresholds in water or air are lower than in food systems due to the increased complexity of the matrix. The stimulus is typically suppressed or overpowered by background volatiles in the base. Therefore, odor activity values should be calculated using threshold measurements determined in the food of interest as opposed to air, water, or other model systems. The composition of "beer" bases varies slightly between sources of published thresholds but all are pale adjunct lagers of less than 5% alcohol by volume (ABV). Literature values do not cover the hop forward styles or variants found in the craft beer sector, especially the highly hopped and higher ethanol, all-malt beers. The role of ethanol content on sensory aroma detection thresholds of odors in beer has not been published. The authors hypothesized that the solvating properties of ethanol would impact sensory aroma detection thresholds of hydrophobic compounds in beer. Hydrocarbons, being especially hydrophobic, would be retained in the higher ethanol beer thereby resulting in higher threshold concentrations. Ten potential character-impact hop compounds were selected to represent a range of chemical classes: (-)-β-carophyllene, (±)-β-citronellol, β-damascenone, geraniol, geranyl acetate, α-humulene, (±)-β-linalool, β-myrcene, nerol and 4-mercapto-4-methylpentane-2-one (4MMP). The olfaction detection threshold of each compound was determined in unhopped pale ale with 5% and 10% ABV using ASTM E679 “best estimate threshold’ standard methodology. Results of this study indicated that ethanol content has little effect on the sensory aroma detection of hop compounds in beer. Ethanol content was not a main effect in the analysis of variance of the combined dataset. The majority of compounds were not influenced by ethanol concentration. Thresholds not exhibiting an alcohol effect, averaged across bases, are: 715 μg/L (-)-β-carophyllene , 42 μg/L (±)-β-citronellol, 480 μg/L geranyl acetate, 317 μg/L α-humulene, 135 μg/L β-myrcene, 6 ng/L 4-mercapto-4-methylpentane-2-one (4MMP) and 869 μg/L nerol. Results of paired comparisons indicated β-damascenone, geraniol and (±)-β-linalool thresholds were significantly influenced by ethanol content. However the practical significance of the 36ppb difference between bases for β-damascenone (195 μg/L in 5% ABV to 74 μg/L in 10% ABV) is uncertain. Interestingly, terpene alcohols increased by up to 2.5 fold with increased ethanol. The threshold of geraniol increased from 141μg/L to 305 μg/L and linalool increased from 83 μg/L to 205 μg/L when more ethanol was present. Our overall conclusion from this work is ethanol content has little effect on the aroma detection thresholds of hop compounds in beer considering compound, assessor and inherent threshold testing methodology variation. In instances where ethanol was significant there may be little potential impact on odor activity values because the 2.5 fold threshold increase was relatively small. Considering these ten hop compounds, more variation was seen in the typically 500 fold difference in individuals' detection thresholds and the 3-10,000 fold difference in reported thresholds between literature sources. Where ethanol concentration clearly has an effect on beer flavor its effect on sensory detection thresholds of hop compounds is minor. The results of this study can be used for OAV calculations across a wide range of ethanol concentrations in beer.
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