The contribution of 4-hydroxyfuranone derivatives to the aroma of commercial beers and malts

Analysis of hot water extracts from a range of commercial malts showed that 2,5-dimethyl-4-hydroxy-3(2H)furanone (DMHF) varied from undetectable (lager malt) to 4.2 mg/litre (crystal malt), a concentration twenty-six times the flavour threshold in water. 5-Methyl-4-hydroxy-3 (2H)furanone (MHF) was detected in all samples except one but was always well under its flavour threshold value. 2(or 5)-Ethyl-5(or 2)-methyl-4-hydroxy-3(2H)furanone (EMHF) was not detected in any of the samples. Fermentation of lager, ale and crystal malt extracts with an ale strain of yeast led to the appearance of EMHF in all cases as well as additional DMHF. The greatest increases in both compounds was with the ale malt. Both increases and decreases occurred in MHF concentration as a result of fermentation but final levels were always well below the flavour threshold value. Analysis of ten commercial beers found DMHF in all the samples and in five cases levels exceeded twice the flavour threshold value in beer with flavour units from 2.4 to 9.1. A flavour panel noted that in four of these cases the beer had a distinctly sweet/caramel aroma which is typical of DMHF. EMHF was undetectable in six samples, detectable, but unquantifiable, in three cases but at about 80% of the flavour threshold value in the remaining sample. MHF was found in all samples but at insignificant levels. The results show that DMHF is an important flavour compound in British ales and EMHF may make a contribution in a limited number of situations. The contribution of malt type, brewery processing and yeast strain in determining the concentration of the two 4-hydroxyfuranones in beer remains uncertain.