A fellow BA sent me a link to a Wired Science blog (Better Beer Through Chemistry: The Search For Noble Hop Aroma Chemicals) that reports researchers from Australia and New Zealand have been working on identifying the chemical compounds that give noble hops their trademark spicy scent.
Target, Saaz, Hallertauer Hersbrucker, and Cascade hop were compared during the tests. According to the article, hops contain upwards of a thousand unique scents, but by using a gas chromatography-olfactometry they managed to isolated 5 terpenes; a class of chemicals responsible for the unique scents found in food, perfumes, and beverages. 1) Geraniol; named after geranium flowers / floral scent. 2) Linalool; floral and spicy; also found in mint, cinnamon, and rosewood. 3) Eugeneol; spicy, clove-like. 4) Beta-ionone; complex woody and fruity scent. 5) Caryophyllene; found in black pepper.
Here are their findings, as reported to the Journal of Agricultural and Food Chemistry ... Comparison of Odor-Active Compounds in the Spicy Fraction of Hop (Humulus lupulus L.) Essential Oil from Four Different Varieties (abstract)
-- The "spicy" character of hops is considered to be a desirable attribute in beer, associated with "noble hop aroma". However, the compounds responsible have yet to be adequately identified. Odorants in four samples of the spicy fraction of hop essential oil were characterized using gas chromatography-olfactometry (GC-O) and CharmAnalysis. Four hop varieties were compared, namely, Target, Saaz, Hallertauer Hersbrucker, and Cascade. Odor-active compounds were tentatively identified using comprehensive two-dimensional gas chromatography (GC×GC) combined with time-of-flight mass spectrometry (TOFMS). An intense "woody, cedarwood" odor was determined to be the most potent odorant in three of the four spicy fraction samples. This odor coincided with a complex region where between 8 and 13 compounds were coeluting in each of the four spicy fractions. The peak responsible was determined by (i) correlating peak areas with Charm values in eight hop samples and (ii) heart-cut multidimensional gas chromatography-olfactometry (MDGC-O). The compound responsible was tentatively identified as 14-hydroxy--caryophyllene. Other important odorants identified were geraniol, linalool, -ionone, and eugenol.