Roasted notes contribute to the flavor of thermally processed foods such as meat and bread. 2-Acetyl-2-thiazoline is one of the key volatile compounds responsible for the roasted and popcorn-like aroma character. We report here on the biogeneration of flavoring preparations with intense roasted notes, which are characterized by a high content of 2-acetyl-2-thiazoline. These flavoring preparations were obtained by fermentation of cysteamine, ethyl-L-lactate, and D-glucose with baker's yeast. The precursor of 2-acetyl-2-thiazoline, 2-(1-hydroxyethyl)-4,5-dihydrothiazole, was prepared under mild conditions by microbial reduction of the carbonyl group of 2-acetyl-2-thiazoline using baker's yeast as biocatalyst. The addition of 2-(1-hydroxyethyl)-4,5-dihydrothiazole as aroma precursor to pizza dough resulted in an increase of the roasted note.