Yeast and Fermentation Session
Frank-Jurgen Methner, TU Berlin
Co-author(s): Katrin Schwarz, TU Berlin, Germany
ABSTRACT: Styrene is a harmful component with a low
carcinogenic potential. Depending on type, the content of styrene in
commercial wheat beers ranges between 0 and 24 ppb. The formation of
styrene, derived from cinnamic acid (CA), occurs as analog with the
decarboxylation of ferulic- and p-cumaric acid to 4 vinylguaiacol (4VG)
and 4 vinylphenol These reactions can proceed both as an enzymatic and
as a thermal decarboxylation. The enzymatic decomposition of CA to
styrene is encoded by the same phenyl acrylic acid decarboxylase (PAD1)
and ferulic acid decarboxylase (FDC1) gene, as the decomposition of
phenol carboxylic acids to the corresponding phenols. Only phenolic
off-flavor positive (POF+) yeast strains, e.g., top-fermenting Saccharomyces cerevisiae,
which are used for wheat beer production, possess these enzymes.
Styrene is quantified with a headspace GC-FID. The hydroxycinnamic acids
and 4VG are determined with HPLC-DAD. The fermentation temperature was
set at 16 and 25°C. The influence on the release of CA during mashing is
determined for the parameter’s temperature (25–80°C), pH (4.2–6.8), and
time (10–300 min). This work should present a practical aid for brewers
to help minimize the content of styrene in wheat beer by optimizing
different fermentation parameters. Higher fermentation temperatures and
an open fermentation management lead to a rapid decrease in styrene.
Fortunately, these two parameters also lead to higher formation of 4VG.
In the case of widely used bottle fermentation, it can be assumed that
the use of POF+ yeast strains will lead to a higher styrene content in
the final beer. Furthermore it could be shown that all available CA in
wort was converted to styrene within a few hours. In addition to the
improvement in fermentation management there is also the possibility to
minimize the formation of styrene by a targeted selection of low-CA malt
and an optimized mashing process. A screening of different malt types
and the influence of temperature, time, and pH on the release of CA
during mashing is also part of this research. These results will be
compared with the existing publications on the release of ferulic acid
during mashing.
Frank-Jürgen Methner conducted studies in
brewing science at Berlin Institute of Technology (TU) from 1975 to
1981. After the studies, he began working as an operating supervisor at
the Schlösser Brauerei, Düsseldorf. From 1982 to 1986, he was a
scientific assistant with teaching duties. Research projects and Ph.D.
thesis, “Aroma Formation of Berliner Weissbier with Special Focus on
Acids and Esters,” were further tasks. For 18 years, starting in 1987,
he held a leading position as a director at the Bitburger Brauerei,
Bitburg, Germany, with responsibilities in fields such as research and
technology, as well as quality assurance. Beginning with the winter
semester 2004/2005 he took over the Chair of Brewing Science within the
Department of Biotechnology at Berlin Institute of Technology (TU
Berlin).
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