Hops (Humulus lupulus L.) are primarily used to provide specific characteristics to beer, such as bitterness, aroma, flavor, and microbial stability. The chemical composition of hops, relative to how they are used during the brewing process, dictates the expression of these characteristics. Of the raw ingredients that go into making beer, hops are perhaps the most costly. Considerable resources are required to grow quality hops, and therefore, brewers and hop growers alike have a common goal of obtaining the highest quality hops possible. However, quality can be a relative term. While it is commonly agreed upon that high brewing values, such as α-acids and essential oil content, and robust structural integrity are indicators of quality hops, there are many opinions of the ideal aroma.
Changes in the chemical composition of hops during plant maturation are a dynamic process requiring a comprehensive, in-depth chemical and sensory analysis in order to maximize the characteristics of interest to brewers. The complex aroma chemistry associated with hops in beer has been
a confounding variable for the practical brewer, and a deeper understanding of hop aroma development during cultivation is needed.
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 3 time points (Early, Typical, and Late), within a 3-week interval from 2 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 Chemist 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 days until harvest. Hop acids did not change appreciably during plant maturation for the period examined, while hop oil content increased hyperbolically to a plateau as the hops aged on the bine. Increases in oil quantity were strongly correlated (r > 0.90) with increases in α-pinene, β-pinene, myrcene, limonene, methyl heptanoate, and linalool concentrations. For Cascade, α-pinene, β-pinene, myrcene, limonene, ρ-cymene, caryophyllene, E, β-farnesene, and humulene
all increased from Early to Typical points but no increase was observed between the Typical and Late time point. Linalool and methyl heptanoate increased between each time point while citral and humulene epoxide differed between Early harvest and Late harvest, but not between Early and Typical or Late and Typical harvests. For Willamette hops, α-pinene, β-pinene, myrcene, limonene, ρ-cymene, and linalool all increased between each time point. Caryophyllene, E β-farnesene, humulene, farnesol and citral all increased from Early harvest to Typical harvest but no difference was observed between Typical and Late.
Clear sensory differences were found between beers brewed with Typical harvest Cascade hops and Late harvest Cascade hops, in terms of difference testing, descriptive analysis and consumer preference tests. / Graduation date: 2013
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37394 |
| Date | 18 January 2013 |
| Creators | Sharp, Daniel C. (Daniel Collier) |
| Contributors | Shellhammer, Thomas H. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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