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Hop Essential Oil: Analysis, Chemical Composition and Odor Characteristics

2009; Elsevier BV; Linguagem: Inglês

10.1016/b978-0-12-373891-2.00022-5

Graham T. Eyres, Jean‐Pierre Dufour,

Horticultural and Viticultural Research

The essential oil of hops (Humulus lupulus L.) imparts odor and aroma characteristics to beer. Hops can influence beer aroma in terms of floral, spicy, herbal, woody and fruity characters. There are a large number of hop varieties commercially available with distinct odor characteristics, which can be attributed to the different composition of their essential oils. This composition is complex, potentially containing up to 1,000 compounds from a wide range of chemical classes. Fresh essential oil is dominated by terpene hydrocarbons, predominantly myrcene, α-humulene and β-caryophyllene. The composition varies depending on: intrinsic and extrinsic factors during growth, processing conditions, and the extraction method used to isolate the essential oil. In addition, oxidation and hydrolysis reactions occurring during storage alter the composition and further increase the chemical complexity. Despite more than 50 years of research, not all character-impact odorants in hop essential oil have been identified. Due to its abundance, myrcene is important for the odor of fresh hop essential oil. Linalool and geraniol have been determined to be important odorants contributing to the floral character of hop essential oil and beer. Other compounds such as β-ionone, β-damascenone, geranial, neral, trans-4,5-epoxy-(E)-2-decenal, 1,3(E),5(Z)-undecatriene, 1,3(E),5(Z), 9-undecatetrene, ethyl 2-methylpropanoate, methyl 2-methyl-butanoate, propyl 2-methylbutanoate, (Z)-1,5-octadien-3-one, nonanal and isovaleric acid have been implicated as potent odorants in hop essential oil. Hoppy aroma in beer is still not completely understood due to the physical, biochemical and chemical changes that occur during brewing and fermentation. Hop-derived odorants identified in beer but not present in hop essential oil include citronellol, γ-nonalactone, humuladienone, geranyl acetate and ethyl cinnamate. Oxidation and hydrolysis products of sesquiterpenes (e.g. humulene epoxides) have commonly been associated with “noble” hop characters in beer; however, the importance of these compounds remains controversial. The complexity of hop aroma in beer has led to increasing trends to add fractionated hop oils with specific odor characteristics to beer post-fermentation.