Styrene is formed by the thermal decarboxylation of cinnamic acid during wort boiling or by enzymatic decarboxylation during fermentation. The enzymatic reaction processes simultaneously to the decarboxylation of ferulic-and p-cumaric acid to clove-like 4-vinylguaiacol and phenolic 4-vinylphenol by the same PAD1 and FDC1 decarboxylase enzymes. However, the formation of styrene occurs much faster within the first hours of fermentation. In addition, the conversion of cinnamic acid starts immediately after pitching without an adaption of yeast on the new medium. Only after 120 min does the level of transposition decrease. Moreover, high cinnamic acid content in pitching wort, in combination with an open fermentation management, causes faster and higher styrene formation during this period. In contrast to the formation of 4-vinylguaiacol, a correlation between pitching rate and styrene formation during open fermentation could be shown. The resulting time interval between styrene and 4-vinylguaiacol formation provides scope for minimization strategies for styrene, while maintaining the typical wheat beer flavours.

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