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- Abstract
- Besides its bacteriostatic effect against Gram+ bacteria and its contribution to beer foam stability, hop (Humulus lupulus L.) is mainly used by brewers to increase bitterness and flavor. For a long time hops have been classified as high bitter or aromatic hops on the basis of the α-acid content. Yet in the past few decades, new dual-purpose varieties characterized by hop cones rich in both α-acids and essential oils have been produced. These dual-purpose hops were a direct response to the growing demand of brewers. After widely studying terpenes and terpenoids (the major constituents of hop essential oils), researches have more recently focused on polyfunctional thiols. These are very pleasant odorant and highly volatile molecules with thresholds below ppb, associating an SH group with an ester, carbonyl, or alcohol function (with a 3-carbon distance in between). Forty-one polyfunctional thiols have now been found in hop, each variety having a unique profile. Surprising increase of such compounds in beer (based on the hopping rate) led investigators to suspect the presence of S-conjugate compounds. After the evidence in hop of the cysteinylated precursors of 3-sulfanyl-4-methylpentan-1-ol (3S4MPol) and 3-sulfanylhexan-1-ol (3SHol), the corresponding S-glutathione precursors were recently discovered in Amarillo, Hallertau Blanc, Mosaic, Citra and Sorachi Ace. In order to optimize the utilization of this high flavor potential, the impact of boiling, primary fermentation, maturation, bottle refermentation and use of enzymes will be discussed.
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