Balance of volatile phenols originating from wood- and peat-smoked malt during the brewing process

The characteristic aroma of smoked malts and, subsequently, of the beers made from them, is mainly derived from phenols, guaiacols, syringols and some furan derivatives. These compounds are the products of pyrolysis, which are transferred to the malt during kilning by the smoke generated through the burning of wood or peat. In the work presented here, the contents of nine characteristic markers in two malts kilned by wood- and peat smoke as well as bottom- and top-fermented beers brewed exclusively from these malts, including intermediate products, were determined using HS-SPME coupled with GC-MS. Significant differences in the content and ratios of specified compounds were found for each type of malt. The peat-smoked malt contained up to 4 times higher levels of most analytes, with significantly higher phenol and cresols (4.2-16.5 mg.kg(-1)) compared to guaiacols (about 2 mg kg(-1)). In contrast, in wood-smoked malt, both groups of compounds were present at comparable levels between 1 and 2 mg kg(-1). During mashing and wort-boiling, levels of volatile phenols decreased by up to 80% of their original amount. Significantly lower losses occurred during fermentation, and no significant differences were found for beers fermented using different yeasts. Nevertheless, most of the differences in the contents of the analysed compounds found in the malts were carried over to the beers. Differences in the composition of beers made from malts kilned using different materials were also confirmed statistically using cluster analysis by comparison with commercially available smoked beers.

Automated summary

The characteristic aroma of smoked malts and beers made from them is mainly derived from specific compounds produced during the smoking process. Different types of smoked malts have significant differences in the levels and ratios of these compounds. During fermentation, these compounds are retained in the beer, resulting in the characteristic aroma.