Graduate Thesis Or Dissertation


Evaluating the Impact of Dissolved Oxygen and Aging on Dry-Hopped Aroma Stability in Beer Public Deposited

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  • It is generally recognized within the brewing industry that hop aroma and flavor in beer changes as beer ages post-packaging. Lager beer staling has been the primary focus of research investigations, with dry-hopped beers receiving limited attention. In the interest of exploring dry-hopped beer staling, this study investigated the impact of dissolved oxygen on the sensory and hop volatile profiles of dry-hopped beers during storage. Dry-hopped beer, which was prepared with low dissolved oxygen throughout its production, was dosed with oxygen in a controlled fashion to create beers with a variety of dissolved oxygen levels ranging from low (40-70 ppb), moderate (70-100 ppb), medium (100-150), to high (>150 ppb) and stored under chilled (3°C) and accelerated (30°C) storage conditions. A sensory panel comprised of 17 participants was used to evaluate the impact of staling on beer after two weeks of accelerated storage. Projective Mapping (Napping®) was used to establish unique Euclidian configurations for each panelist, and ultra-flash profiling helped to enrich the product map with sensory descriptors. Sensory results very clearly identified storage temperature, used as a proxy for aging duration, as having the greatest effect on aromatic changes during storage. DO concentration was also observed to have a lesser, but significant, impact at both high and low storage temperatures after only two weeks of aging. Higher storage temperature and dissolved oxygen concentrations resulted in a loss of tropical, citrus and hoppy characteristics and the production of malty, dried fruit and cardboard aromas. Analytically, haze and color increased with increasing DO, while bitterness units (BUs) decreased. Hop derived monoterpenes were not significantly affected by treatment temperature or dissolved oxygen, suggesting stale character expression from alternate sources (lipid oxidation, and/or Strecker aldehydes).
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