M. Shaun Townsend

Effect of Harvest Maturity on the Chemical Composition of Cascade and Willamette Hops

Considerable expertise is required to grow high-quality hops, and brewers and hop growers alike have a common goal of obtaining the highest quality hops possible. Changes in the chemical composition of hops during plant maturation is a dynamic process requiring a comprehensive chemical and sensory analysis in order to maximize the characteristics of interest to brewers. The effect of harvest date, location, and cultivar on key chemical components of Willamette and Cascade hops was investigated for the 2010 and 2011 growing seasons. Hops were harvested at three time points (early, typical, and late) within a 3 week interval from two different farms in the Willamette Valley, Oregon. A split-plot experimental design for each cultivar was used; each farm represented a main plot and harvest years were designated as subplots. American Society of Brewing Chemists standard methods of analysis were used to measure moisture content, hop acids and their homologs, hop storage index, total essential oil content, and volatile profile by GC-FID. Additionally, difference testing, descriptive analysis, and consumer acceptance testing was conducted using beers brewed with either typical or late harvested Cascade hops from the 2010 harvest year. The response of analytes was dependent on the cultivar being examined, its location within the Willamette Valley, as well as timing of harvest. Hop acids did not change appreciably during plant maturation for the period examined, while hop oil content increased. Increases in oil quantity were strongly correlated (r > 0.90) with increases in α-pinene, β-pinene, myrcene, limonene, methyl heptanoate, and linalool concentrations. Clear sensory differences were found between beers brewed with typical and late harvested Cascade hops using triangle testing, consumer preference testing, and descriptive analysis.

Potential Heterotic Crosses in Hops as Estimated by AFLP-Based Genetic Diversity and Coefficient of Coancestry

Hop is a dioecious perennial with female plants grown commercially for brewing purposes. Parent selection in hop breeding on the basis of heterotic potential has not been reported in literature even though dominance has been reported in hops for several economically important traits. The objectives of this study were to determine if amplified fragment length polymorphism (AFLP)-based genetic distance among male and female accessions accurately reflect pedigree relationships and present information on potential heterotic crosses in hop. Nineteen cultivars were analyzed for genetic distance to 82 male accessions representing the assumed diversity of U.S. hops. Genetic distances (GD) between male/female pairs were estimated using AFLP (490 polymorphic bands). Distance estimates comparing males with females ranged from 0.169 to 0.62 with an overall average of 0.306. For each hop female, the 10 most genetically diverse and 10 most genetically similar males were identified and grouped. Coefficients of coancestry (COA) for each male/female pair within these groups were calculated using pedigree analysis. Values of COA for the genetically similar pairs (COAavg = 0.046) were significantly higher than the COA for the diverse pairs (COAavg = 0.013), suggesting that choosing male/female pairs on the basis of AFLP-based genetic distance may predict heterotic potential in crosses when GD >0.36.