Biosynthesis of flavour-active furanones by Saccharomyces cerevisiae during fermentation depends on the malt type used in medium preparation

Extracts of a coloured malt contained 4-hydroxy-5-monomethyl-3(2H)-furanone (HMMF), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) but not 4-hydroxy-5(or 2)-ethyl-2(or 5)-methyl-3(2H)-furanone (HEMF). Extracts of a pale malt did not contain any of the furanones. HMMF and HDMF were produced by Saccharomyces cerevisiae during fermentation of both types of malt extract. About 0.09 mg HEMF I^-1 was synthesised during fermentation of the coloured malt extract but none was produced with the pale malt extract. Final concentrations of HDMF (2.0 mgl^-1) and HEMF (0.09 mgl^-1) were in excess of their aroma threshold values in water (0.16 and 0.02 mgl^-1 respectively) after fermentation of the coloured malt extract.