Behaviors of 3-Mercaptohexan-1-ol and 3-Mercaptohexyl Acetate during Brewing Processes

Abstract

The behaviors of 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) during brewing processes were examined to establish their contributions to the distinctive beer aroma. In hops, 3MH was detected in both U.S. and European cultivars. The concentration differed between cultivars, ranging from 10 to 120 μg/kg of pellet, whereas the occurrence of 4-mercapto-4-methylpentan-2-one (4MMP) depended on the growing region as well as the cultivar—4MMP was not detected in European cultivars. The addition of copper granules to beer indicated that 4MMP was more susceptible than 3MH to binding with copper, which may corroborate the fact that the growing regions of cultivars have little effect on 3MH content. During the boiling process of hopped wort, the 4MMP content decreased, whereas the 3MH content increased at a faster rate at 100°C than at 90°C. During fermentation, the 3MH and 4MMP contents increased and peaked at an early stage of the process. 3MH also was detected in measurable amounts in the hop pellets of all cultivars and in unhopped beer but not in unhopped wort. This finding indicates that both malt and hops are a source of 3MH precursors. Little or no 3MHA was detected in hop pellets. It was revealed that 3MHA was synthesized during fermentation from 3MH and had a lower threshold value than 3MH. This study suggests that selecting yeast strains with a high ability to convert thiols from 3MH to 3MHA is a useful strategy to increase the aroma impact of beer.