Key steps during barley malting that influence the concentration of flavor compounds

The production of the three potential flavor compounds 5-methyl-4-hydroxy-3(2H)-furanone (MHF), 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF), and 5(or 2)-ethyl-2(or 5)-methyl-4-hydroxy-3(2H)-furanone (EMHF) during the malting of barley was investigated. Malts were germinated for different lengths of time and kilned using a variety of regimes. The hot-water extracts of the malts were extracted with methyl acetate and analyzed by gas chromatography-mass spectrometry. It was demonstrated that both germination and kilning were essential for the formation of MHF and DMHF, as neither green malt, raw barley, nor kilned raw barley contained these flavor compounds. EMHF was not detected in any of the samples tested. The levels of MHF and DMHF detectable in the malt were shown to increase as the length of germination increased up to 66 hr, after which the furanone content declined. Low-temperature kilning gave rise to little or no furanones, as did roasting over short periods. However, if the green malt was stewed before roasting, the levels of DMHF in the hot-water extracts increased to above that of the aroma threshold in water. The highest concentration of MHF was 19% of its aromas threshold.