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).