Jörg Maxminer (1),
Johanna Koserske (1), Nils Rettberg (1), Sarah Thörner (1); (1)
Research and Teaching Institute for Brewing in Berlin (VLB), Berlin,
Germany
Technical Session 17: Beer Aging
Tuesday, August 16 • 3:30–5:15 p.m.
Plaza Building, Concourse Level, Governor’s Square 14
The aroma of beer is a major quality characteristic that is commonly
described as a complicated puzzle with hundreds of pieces. Beer as
manufactured is not at chemical equilibrium and undergoes complex
chemical reactions during storage, which can lead to undesirable changes
in sensory characteristics. This phenomenon largely remains a mystery
and is a major challenge for the brewing industry in the effort to
supply a consistent product to consumers. Certain aldehydes are
essential for the perception of staleness and can be directly linked to
undesirable sensory attributes as their concentration increases during
storage. When it comes to the analysis of staling aldehydes, their
volatility, reactivity, but most importantly their low concentration
(µg/L to ng/L) in a complex beer matrix, has challenged brewers for
decades. Doubtless, gas chromatography-mass spectrometry is a
well-established tool for the analysis of staling aldehydes; however,
drawbacks in selectivity and sensitivity can hinder the reliable
quantification of those aldehydes related to undesirable “aged flavor.”
These drawbacks might be circumvented when using headspace solid-phase
microextraction combined with gas chromatography and tandem mass
spectrometry (HS-SPME-GC-MS/MS), which is a new tool in brewing
analysis. The performance in the sub-ppb range increases enormously
using this analysis technique. The current presentation gives a detailed
insight into an improved method for the analysis of staling aldehydes
utilizing a HS-SPME step and on-fiber derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine
hydrochloride (PFBHA). The oxime derivatives formed on the fiber are
thermally disport, followed by gas chromatographic separation coupled to
a GC-MS/MS. Selecting specific fragment ions within the electron
ionization (EI(+)) mass spectra of these oxime derivatives as precursor
ions for MS-MS fragmentation provides a suitable method for the target
analysis of individual aldehydes. Employing isotope standard
d5-phenylethanal as an internal standard increases the reproducibility
and is a unique feature of this tandem mass spectrometry technique. In
the present study, the method was verified for 15 different staling
aldehydes by analyzing 4 different beer styles (alcohol-free, lager,
dark and ale) fresh and after 1 and 2 weeks of storage at 40°C. Low
limits of quantification (down to 25 ng/L) and a wide working range (up
to 250 µg/L) could be accomplished for certain aldehydes in all 4 beer
matrices. The very low standard deviations (<10%) and high linearity (R2
> 0.99) achieved for all evaluated aldehydes is a major advantage of
this technique compared to any other method previously described. The
above data highlight the advantages of this promising measuring
technique (e.g., selectivity, sensitivity, automation) and its
possibilities to gain further understanding about the complex chemistry
of beer aging and in the hunt for improved flavor stability.
After receiving a Dipl.-Ing. (FH) degree in beverage technology
from the University of Applied Science Wiesbaden-Geisenheim (Germany),
Jörg Maxminer worked at the Karlsberg Brewery in Homburg (Germany) in
the Technology and Development Department for two years. In 2011 he
graduated from Heriot-Watt University Edinburgh (U.K.) with an M.S.
degree in brewing and distilling. Jörg is currently working toward a
Ph.D. degree at the University of Nottingham (U.K.) with a research
focus on flavor stability of lager-style beers. In addition, Jörg is
employed as head of the department for the central laboratory at the
Research Institute for Instrumental Beer and Beverage Analysis at the
Research and Teaching Institute for Brewing in Berlin (VLB) (Germany).
Here he manages the standard beer analysis and is involved in different
research projects with a focus on beer flavor. Aside from work, Jörg
enjoys brewing his own beer and playing handball.
