A gene {POFl) has been cloned, which confers upon yeast {Saccharomyces cerevisiae) the ability to decarboxylate phenolic acids such as ferulic and trans-cinnamic acid. This property was previously shown to be a cause of phenolic off-flavour production in wort fermentations. The identity of the cloned gene was confirmed as POF1 by gene disruption techniques. Southern blotting of total genomic DNA revealed that sequences homologous to POF1 are conserved in Pof" brewing strains of Sacch. cerevisiae. The transformation of a Pof" lager strain with the cloned POF1 gene led to the production of an aroma characteristic of a phenolic off-flavour, when the transformed strain was used in wort fermentations. This latter observation suggests that the Pof~phenotype of brewers' yeast is specifically due to the absence of a functional POF1 gene.