Program Book - Master Brewers Association of the Americas

P-74
Optimized analytical methods for the determination of SO 2 in
beer and malt
THOMAS KUNZ (1), Victoria Schiwek (2), Frank-Juergen Methner
(1)
(1) TU Berlin/VLB Berlin, Berlin, Germany; (2) VLB Berlin, Berlin,
Germany
The determination of the SO 2 content in beer is becoming more
of a focus for brewers. The technological importance of SO 2 is
based on its anti-oxidative potential, which protects beer against
oxidation and therefore enhances flavor stability. However SO 2
is said to have some allergenic potential, especially for sensitive
individuals it may cause hives, stomach problems and a headache,
even though the content in beer is considered to be harmless from
a physiological point of view. Nevertheless the allergenic potential
has provoked a European directive, which is limiting the content
of SO 2 and sulfites to a concentration of 10 mg/L, otherwise it has
to be labeled. Based on these backgrounds, different analytical
methods for the determination of SO 2 were compared among each
other according to their accuracy, application, linearity, precision
and selectivity and have been optimized. The oldest and most
used analysis in brewing is the distillation method according to
Monnier-Williams. Due to the high expenditure of time, personnel
costs and a recovery rate of ≈90% this analysis is less suitable for
determination in beer. Opposite to that for determination in malt
it is more appropriate, because there is no adequate possibility of
extracting the SO 2 from the malt without higher losses. Comparative
measurements using whole malt kernels show significantly higher
yields with much lower coefficients of variation compared to fine
and coarse grist. The reasons are the oxidation of the SO 2 during the
milling process and mainly the fact that in the flask agglutination
occurs by fine and coarse grist in contrast to whole malt kernels.
It is generally possible to determine the SO 2 content in whole malt
kernels, because of the fact that the SO 2 is primarily located in
the husks. The suitability of the new method could be confirmed
in several interlaboratory tests. Photometric analysis via CFA
(continuous flow analysis), using pararosaniline, is another possible
method. This method showed significantly higher results for SO 2
in beer compared to the distillation method. These higher results
can be explained by the occurrence of background signals caused
by the beer matrix. It could be demonstrated that the background
signals are mainly caused by Maillard reaction products in the
beer. By using new developed Teflon membranes it was possible
to eliminate the interfering signals almost completely and led to a
significant increase in the sensitivity of this method. In recent years,
ion chromatography (IC) has been established more and more in
breweries for the determination of SO 2 . IC is characterized by a low
standard deviation, good reproducibility of the individual values and
a good recovery of up to 100%.
After qualifying as a certified technician in preservation engineering
(1991–1993), Thomas Kunz completed his basic studies in chemistry
at Isny University of Applied Sciences (1994–1995) and his basic
studies in food chemistry at Wuppertal University (1995–1998)
before starting to study food technology at Trier University of Applied
Sciences (1998–2002). After graduating, he worked as an engineer
(Dipl.-Ing. FH) in the area of ESR spectroscopy at the Institute of
Biophysics at Saarland University (2002–2004). Since January
2005, he has been employed as a Ph.D. student at the Research
Institute for the Technology of Brewing and Malting at VLB/
Technical University of Berlin under the supervision of Professor
Methner. His main research focus is analysis of radical reaction
mechanisms in beer and other beverages using ESR spectroscopy.
P-75
Brewing industry quality control applications using headspace
sampling/gas chromatography
TOM KWOKA (1), Ruth Martin (2), Tim Ruppel (1)
(1) PerkinElmer LAS, Shelton, CT; (2) Sierra Nevada Brewery,
Chico, CA
There are four major HS/GC analyses that are performed at
breweries for the purpose of quality control and identifying
problems or changes occurring in brewing and fermentation
processes that can adversely affect both the taste and quality of
the final product. The first and perhaps most important of these
is monitoring for vicinal diketones (VDK’s) in beer. VDK’s are
known to affect the taste of beer, imparting a butter-like flavor
that is considered undesirable at higher concentrations. Generally
speaking, heavier beers, including stouts etc., tend to have higher
levels of VDK’s than do lighter beers. Typically, VDK’s are found in
the 1–50 ppb range in lighter beers and can exceed several hundred
ppb in darker beers. Acetaldehyde is a further analysis performed
throughout the brewing process. Acetaldehyde is reduced to
ethanol by yeast during secondary fermentation, but oxidation of
the finished beer may reverse this process, converting ethanol back
to acetaldehyde. The taste and aroma of acetaldehyde has been
described as fresh cut green apples, grass, leaves and even latex
paint. Levels of acetaldehyde are generally in the 1–20 ppm range.
A third group of compounds of interest are the trihalomethanes.
These are usually introduced into the beer through the municipal
water supply. Municipal water is often treated with chlorine,
resulting in a variety of chlorinated disinfection by-products.
Chloroform is usually the most prominent trihalomethane identified
during this analysis. The fourth test commonly performed on beer
is the isolation and identification of sulfur compounds. Dimethyl
sulfide (DMS), sulfur dioxide (SO 2 ) and hydrogen sulfide (H 2 S) are
of particular interest to brewers worldwide. DMS has the taste and
aroma of sweet corn. This comes either from the malt, as a result
of a short boil of the wort, slow wort chilling or bacterial infection.
SO 2 is often used as a preservative. Various types of yeast will
produce significantly different levels of H 2 S. Above very low ppb
levels, these sulfur compounds give off an unpleasant taste and
smell (e.g., rotten eggs). Though traditionally these four QC tests
have been performed individually, the use of the PerkinElmer HS/
GC allows for the combining of these analyses, thus dramatically
enhancing productivity. In fact, depending on one’s desired level
of detection, all four methods can be analyzed simultaneously or, if
need be, broken up into method specific parameters. The improved
application will be described and criteria for performance and
quality control will be outlined.
Tom Kwoka received a B.S. degree in chemistry from California
State University, Sacramento, in 1983. He began employment with
PerkinElmer, Inc. in 2004 as a chromatography product specialist.
Tom’s current functions include pre-sales support, post-sales
customer training, and applications development. Tom has 19 years
of environmental laboratory experience, including QA/QC, GC, and
GC/MS analysis.
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