According to Wired Science, scientists from Down Under (the Department of Food Science, University of Otago, in Dunedin, New Zealand, and the Australian Centre for Research on Separation Science, Department of Applied Chemistry, RMIT University, in Melbourne, Victoria, Australia more specifically) have published a paper identifying the chemicals creating the spicy aromas in noble hops using four different hop varieties: Target, Saaz, Hallertauer Hersbrucker, and Cascade. (That’s what’s being reported, target and cascade, of course are not noble hops.) They’ve now succeeded in finding the chemicals responsible for “spiciness,” using “two-dimensional gas chromatography mass spectrometry.” The equipment takes “individual chemical[s] from the hops in a two-step process, and then weighs the individual molecules to identify them.” There are nearly 1,000 separate chemical components that contribute to the aromas just from hops so this was definitely like looking for the proverbial needle in a haystack.

Dr. Lingshuang Cai and Jacek Koziel at Iowa State University

From the Wired article: When the test results came in, five chemicals stood out from the others. All of them are terpenes. Geraniol, which is named after geranium flowers and obviously has a floral scent. Linalool, has a floral and spicy scent. It is also found in mint, cinnamon, and rosewood. Eugeneol has a spicy, clove-like aroma. Beta-ionone has a complex woody and fruity scent. Caryophyllene is found in black pepper. Terpenes are a class of chemicals that are often responsible for the unique scent of food, perfume, and beverages. In 2002, other researchers showed that adding a tiny amount of a particular terpene to a very bland beer made it smell fantastic, but not quite as complex as a premium brew.

From the Abstract in the Journal of Agriculture and Food Chemistry:

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-ß-caryophyllene. Other important odorants identified were geraniol, linalool, ß-ionone, and eugenol.