Graduate Thesis Or Dissertation
 

Factors that Influence the Sensory Characteristics of Dry-hopped Beer

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  • When hops are added to beer, varying degrees of hoppy aroma persist in the finished beer as a result of a number of factors. Dry-hopping is a technique whereby hops are added to beer post-fermentation to leverage the maximum aroma potential of the hop essential oils while minimizing bitterness contribution from the hop alpha acids. Brewers are very interested in understanding dry-hopping as this practice is widely used throughout the industry. The studies herein investigate both the dry-hop process as a vehicle to dose flavor and aroma into beer and hop/processing factors that contribute to this operation. Hop oil serves as the primary reservoir of aromatic compounds in the hop plant and it is hypothesized that using hops with greater total oil content will result in more hoppy aroma in dry-hopped beers. An unhopped beer was dry-hopped with 23 individual Cascade hop lots and was evaluated using sensory descriptive analysis. There was no correlation between total oil content (ml oil/100g hops) and overall hop aroma intensity (OHAI). Therefore, the specific volume of hop oil in hops is an inadequate indicator of hoppiness potential in dry-hopped beer. Cascade, Chinook, and Centennial hops are some of the most popular American hops used by brewers across the globe. Because of their high use, there exists a need to understand how the hop-derived, analytical profile of these cultivars in the beer system can be used to enhance quality assurance strategies. An in-depth flavor analysis approach utilizing Solvent-Assisted Flavor Evaporation (SAFE) and Aroma Extract Dilution Analysis (AEDA) was carried out to understand which compounds contribute the most to the character of these hops in the dry-hopped system. The analysis revealed Cascade, Chinook, and Centennial had 9, 10, and 11 character impact compounds (CIC). Commonalities were observed among the three cultivars regarding 2-furanmethanol, linalool, geraniol, cis-geranic acid methyl ester, and n-decanoic acid in beer. Variation between the Centennial and Chinook cultivars is a function of only a few character impact compounds whereas Cascade is markedly different, anchored heavily by benzenacetaldeyde. This knowledge could help introduce potential replacements, removals, and/or reductions for these hop cultivars in the future. When stored under pro-oxidative conditions, qualitative changes in the chemical and aroma profile of Hallertauer Mittelfrüh (HHA) hops occurs. It was hypothesized that lager beer dry-hopped with oxidized HHA would impact both the qualitative attributes related hop aroma in the finished beer and influence consumer acceptance. Lager beer was dry-hopped using oxidized hops and a non-oxidized control at two different hopping rates (3.8 g/L, 1.5 g/L). Trained panelists using descriptive analysis evaluated the beer dry-hopped at 3.8 g/L. At this dosing rate, significant qualitative changes were observed in the beer as a result of using oxidized hops. The beers dry-hopped with the oxidized hops had significantly higher sensory ratings for woody and herbal attributes, which are associated with “noble” hop aroma. 60 consumers rated their acceptance of the beers dry-hopped at a lower rate of 1.5 g/L and no significant difference in overall liking was found between the hop preparations. While changes in hop chemistry occur as a result of oxidation, these changes may not adversely affect overall liking of beer prepared with oxidized hops but may serve as a way to enhance noble hop aroma in lager beer. Dry-hopping can be used as a method to assess the aroma potential of a hop cultivar, for instance as a tool used during the late stages of the hop breeding process or as a way to determine beer performance of a prospective hop cultivar when evaluating hops pre-purchase. These evaluations, though quick, are commonly prone to high variation. From a hop perspective, more effective sampling and preparation techniques were implemented to reduce within lot variation and increase homogeneity. From a processing perspective, increased volumes of liquid, duplicate dry-hopping events, blending and filtration methodology, as well as oxygen control have reduced the process derived variation. The Oregon State dry-hopping method has evolved to best display hop material in dry-hopped beer in an accurate and precise manner as well as reveal the variable nature of small-scale hop evaluations.
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