Formation of sweet flavor compounds during fermentation

The sweet flavor compounds present in lager beer and the variation in their concentrations during fermentation was investigated. Lager beer was extracted with methylene chloride. The extract was separated by liquid-liquid extraction into four fractions. The fractions were analyzed by gas chromatography-olfactometry and combined gas chromatography-mass spectrometry. The compounds 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF), 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF), and maltol were identified as having a caramel-like sweet flavors and aromas. HDMF and maltol were present in wort, but HEMF was not detected. The concentration of HEMF increased during fermentation as wort gravity was increased. Also, the concentration of HDMF increased during fermentation when certain brewing yeast strains were used.