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.
Craft breweries that tend to convince consumers with new interpretations of (ancient) beer styles increasingly influence the traditional beer market. Thereby, also ingredients not directly compliant with German beer purity laws come into use. Official food control currently faces the general problem of verifying food authenticity based on instrumental analytical methods. Related tasks in this field are the detection of non-labelled ingredients and the verification of product claims such as special food processing methods. For that purpose, chemometric analysis of high-resolution 1 H NMR spectra was applied for the differentiation of related beer styles including also special beers. It could be shown that pilsner style beers, wheat beers, India pale ales, sour beers, and special beers can be easily differentiated applying consecutive principal component analysis. Thereby, it turned out that crafted pilsner style beers are distinguishable from industrial pilsner style beers based on their organic acid profiles. Furthermore, three conspicuous compounds present in two different batches of only one of the beer samples were identified as allyl alcohol, 1,3-propanediol, and 3-hydroxypropionic acid directly from the NMR spectra without any further analytical efforts. Finally, the present paper serves as a proof of concept that NMR-based quantification is also possible using chemical shift information instead of signal intensities/integrals-at least in special cases.
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