LANCE T. LUSK (1), Susan B. Kay (1), David S. Ryder (1)
(1) MillerCoors, Chicago, IL
Numerous compounds that are subject to concentration changes have
been suggested as markers of beer flavor instability. The subset of
these compounds with a flavor impact is much smaller and includes
compounds such as trans-2-nonenal (cardboard aroma) and methional
(potato aroma). In the current work, GC×GC-olfactometry-MS was used to
identify significant changes in aroma compound levels as beer aged. The
key was to search for the significant changes in aroma, not necessarily
the most intense aromas. A further challenge was confirming the chemical
identity of low levels of flavor-active compounds buried in a
chromatogram under much higher concentrations of compounds without
flavor impact. The challenge was met through knowledge of the aroma,
analysis of standard compounds (when available), and statistical PCA
mapping of MS ions from narrow GC time windows. Compound identity was
further confirmed using GC×GC-time-of-flight-MS. The beers used for this
work did not develop typical cardboard aroma, and trans-2-nonenal was
not one of the compounds identified. The compounds that significantly
increased or decreased in aroma during 12 weeks of forced aging at 30°C
were methyl mercaptan, methional, dimethyltrisulfide,
phenylacetaldehyde, 1,1,6-trimethyl-1,2,3,4-tetrahydronapthalene (TMTN),
citronellyl acetate, and δ-cadinene. TMTN is a flavor-active
norisoprenoid oxidation product of carotenoids. This is an example of
the oxidation product of an antioxidant contributing to oxidation
character. δ-Cadinene is a minor sesquiterpene in hop oil. During beer
fermentation, yeast biotransformation of hop-derived monoterpene
alcohols leads to β-citronellol, which would provide a source for
esterification to citronellyl acetate. Other researchers previously
showed that methyl mercaptan, methional, dimethyltrisulfide, and
phenylacetaldehyde contribute to beer oxidation aroma. The validity of
the importance of this group of compounds as key olfactory cues for beer
oxidation was demonstrated by the excellent multivariate analysis
correlation (R2 = 0.99) between the sensory panel
scores (for oxidation increases over 12 weeks) and the flavor stability
compound level changes (MS-selected ion monitoring values).
Lance Lusk is an internationally recognized expert in beer flavor
stability and foam properties. He is also an experienced brewery process
troubleshooter and product and process improvement innovator. He has
extensive knowledge of beer flavor gained through gas
chromatography–mass spectroscopy–olfactometry analysis, as well as
extensive experience with electron spin/paramagnetic resonance
spectroscopy for beer free-radical analysis. He held various positions
at Miller Brewing Company (now MillerCoors) for more than 29 years until
his retirement. He is now a brewing consultant. Lance is a member of
six professional societies, including ASBC and MBAA. Lance is the
recipient of seven U.S. patents, the 1996 ASBC Eric Kneen Award, and the
2010 ASBC Honorary Life Membership Award. He has presented his work at
ASBC and EBC meetings and the Jean de Clerck Chair. Lance’s former
interns include brewing professionals on three continents, a medical
doctor, and the director of consumer insights at a major producer of
flavors and fragrances.
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