Dry Hopping with the Dual-Purpose Varieties Amarillo, Citra, Hallertau Blanc, Mosaic, and Sorachi Ace: Minor Contribution of Hop Terpenol Glucosides to Beer Flavors

The dual-purpose hop varieties Amarillo, Citra, Hallertau Blanc, Mosaic, and Sorachi Ace were recently shown to contain unusually high amounts of some discriminating terpenoids, polyfunctional thiols, and precursors of the latter (cysteine and glutathione adducts). The present work aimed to investigate the terpenol glucoside fraction in hops and its potential contribution to beer after a dry hopping process. Terpenols were quantified by stir-bar sorptive extraction GC-MS in five pilot monovarietal dry-hopped beers. In all of them, linalool and geraniol were found above their sensory thresholds (72-178 and 7-57 mu g/L, respectively, for a threshold of 8 mu g/L for linalool and 4 mu g/L for geraniol). beta-Citronellol also exceeded its threshold when the Amarillo, Citra, or Sorachi Ace cultivars were used. The hop glucoside potential was analyzed by GC-MS after enzymatic degradation. A relative hydrolysis efficiency factor was applied to our data to take into account that the commercial beta-glucosidase releases octan-1-ol, used here as an internal standard, 2.8 times more efficiently than geraniol. beta-Glucosidase treatment caused the release of linalool, alpha-terpineol, beta-citronellol, and geraniol from all five dual-purpose cultivars, but in much lower amounts than the corresponding free terpenols (0.6-28.6 mg/kg of aglycons versus 7.8-109.2 mg/kg of free forms). Further quantitative analyses focusing on more traditional aromatic and bitter hops are now needed to compare their glucoside fractions with those here investigated.