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.
--
On the surface this is all very cool, in an über-beer-geek-learning-
more-about-beer kind of way, but it does bring up some questions and
concerns as to how findings like these could be applied to hops and
brewing. In my opinion, if a brewer wants the unique characteristics
found in noble hops in their beer: use noble hops. We already have
enough man-made junk (aka shortcuts) in our lives, under the guise of
progress and "improving" the quality of the products in our lives. The
last place I want them is in my beer.
http://beeradvocate.com/smack/archives/2007/08/1056934