FRANK-JÜRGEN METHNER (1), Katrin Schwarz (1)
(1) Berlin Institute of Technology (TU Berlin), Berlin, Germany
Styrene, which is created by phenylalanine during mashing and wort
boiling or by the enzymatic decarboxylation of cinnamic acid during
fermentation, has been classified as “possibly carcinogenic to humans”
by the IARC. The average concentrations of styrene in commercial wheat
beers range between 3 and 24 µg/L and increase up to 65 µg/L during
fermentation (temp. ADI 4 µg/kg BW). Previous analyses also showed that
darker beer has a higher styrene concentration than pale beer. However,
there was no linear correlation between the cinnamic acid and
phenylalanine concentration in wort and the styrene concentration in
finished beer. Concluding from this, there is evidence that the
formation of styrene mainly depends on the applied mashing, wort
boiling, fermentation and maturation process. First of all, the employed
yeast strains and the temperatures during fermentation are important
factors. This is confirmed by fermentations with different
top-fermenting yeast strains, e.g. W68 with and without the addition of
cinnamic acid. 4-vinyl guaiacol and 4-vinyl phenol, two of the main
aroma compounds of wheat beer, are created by the enzymatic
decarboxylation of ferulic and p-coumaric acid during fermentation. The
level of these phenolcarboxylic acids and therefore the concentration of
aroma compounds in beer depends on the used wheat fraction and the
roast intensity. While styrene is formed at the beginning of the
fermentation, the other 4-vinyl-derivates are not created in greater
quantities until the cinnamic acid is completely converted. Styrene
reaches its peak after 24 h while the concentrations of 4-vinyl guaiacol
and 4-vinyl phenol accumulate during the whole fermentation process.
Excluding the influence of other decarboxylases, the results may prove
that cinnamic acid has a higher enzyme affinity than ferulic and
p-coumaric acid.
Frank-Jürgen Methner studied brewing science at Berlin Institute of
Technology (TU Berlin) from 1975 to 1981. After finishing with a
Dipl.-Ing. degree, Methner began working as an operating supervisor at
the Schlösser Brauerei, Düsseldorf. From 1982 to 1986 he was a
scientific assistant with teaching duties at the Research Institute for
Brewing and Malting Technology of the VLB in Berlin. For 18 years,
starting in 1987, Frank-Jürgen has held a leading position as a director
at the Bitburger Brauerei, Bitburg, Germany, with responsibilities in
fields such as technology and quality assurance. Beginning with the
winter semester of 2004/2005 he took over the chair of brewing science
at TU Berlin.
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