The German hop Hallertauer, hallertauer is highly valued because of its "noble aroma", but it has a very low yield when cultivated in the U.S. Two new crosses of Hallertauer, U.S.D.A. 21455 and 21459, have high yields and promising aroma characteristics. In order to predict sensory properties of beers as a function of the varieties of hop used in brewing, a more complete sensory and chemical characterization of hop oils is necessary. The aims of this study were to compare the aroma profiles of the new crosses against the German variety by determining their most important odor active compounds, and correlating the sensory attributes evaluated by a descriptive sensory panel (DSP) with the odor intensities detected during the gas chromatograph (GC) effluent detected during the gas chromatograph (GC) effluent sniffing. Oxygenated fractions were spiked into spring water and evaluated by the DSP. The same samples were injected into the GC and the effluents were evaluated quantitatively and qualitatively by four subjects using a special data collection device. Samples were then analyzed by mass spectrometry (MS). There were no significant differences among the three varieties based upon the DSP results and the "aromagrams" obtained during the sniffing of the GC effluents. Important odor active peaks were associated with humulene oxidation products. A number of statistical correlations existed between the sensory attributes and the odor active peaks. In summary, the new varieties are potential contributors to "noble aroma". Trials with beers brewed with these hops are underway in order to establish their contribution to beer flavor. / Graduation date: 1990

This work set out to examine the methodologies of dry hopping, compare different hop materials, and look at the extraction behavior of different types of hop compounds. This work consists of two discrete studies, where the first study informed the design of the second. The first study measured the concentrations of hop aroma compounds extracted from Cascade hops during dry hopping using a model beer system devoid of malt, yeast aromas, and hops. Cascade hops pelletized by four different processors yielded different particle size distributions and pellet densities. These pellets were dosed into a degassed medium (water, 6% v/v ethanol, pH 4.2) and the hop aroma extraction was measured periodically over a one week period. Solid phase micro-extraction (SPME) followed by gas chromatography (GC-FID) was used to analyze the levels of aroma compounds in the extraction medium. Variation in the hop pellet physical properties did not significantly impact the extraction rate of hop volatiles such as linalool, geraniol, limonene and myrcene with one exception. One treatment showed an increased absolute concentration of geraniol. Separately, dry hop aroma extraction was measured over a short time (1 day) at room temperature in an unhopped beer using small-scale (1L), stirred vessels. Irrespective of the hop form (whole or pellet), the concentrations of hydrocarbon terpenes peaked between 3 and 6 hours and subsequently declined, while the concentrations of terpene alcohols continued to increase throughout the 24 hour dry hop extraction. The rate of hop aroma extraction did not appear to be significantly influenced by hop pellet properties and occurred rather rapidly regardless of the hop form. The second study examined the extraction of hop aroma compounds during a pilot brewery scale (~4hL) dry hop treatment. Dry hop treatments consisted of whole cone hops and pellet hops (Cascade cultivar, 2011 harvest) which were dosed into cylindroconical vessels which were either stirred with a pump or left quiescent. Samples were taken for GC-FID and HPLC analysis as well as sensory evaluation at various time points between 30 minutes and 12 days. Polyphenol and alpha acid extraction was highest in a stirred system dosed with pellets. Hop aroma compound extraction was also the highest in the stirred system utilizing pellet hops. The sensory panel rated the stirred pellet samples as having the highest hop aroma, bitterness, and astringency. The results showed that hop flavor from dry hopping can be readily achieved with much shorter contact time than the current 4-12 day industry practice. / Graduation date: 2013