Aging of hops and their contribution to beer flavor

Abstract

Two American hop varieties, Washington-grown Cascade and Idaho-grown Hallertauer mittelfriih, were chosen for this aging study and its effect on beer flavor quality. Prior to brewing, hops were refrigerated at 27 °F (fresh), while one portion of the hops from the same bale was aged at 90 °F for 2 weeks (aged I) and another portion for 9 weeks (aged II). Samples at each brewing stage were taken for chemical profile analysis. The finished beers were also submitted for flavor profile evaluations. Geraniol, linalool, and citronellol are mainly responsible for the floral/citrus note, while the oxidation products of a-humulene, especially the humulenol II and humulene diepoxides, contribute to the herbal/spicy note in beer. A grapefruit-like fruity flavor is also detected in beers brewed with extensively aged Cascade and Hallertauer hops. The survival of various hop-derived aroma compounds is also discussed.

High content of zerumbone in volatile oils of Zingiber zerumbet from southern India and Malaysia

“…Humulene epoxides and humulenols, found in all seven Z. zerumbet accessions, contribute to their herbal, aromatic note as humulene derivatives in hops (Humulus lupulus) contribute to the spicy note in beer and other beverages. [40] Yu et al [41] reported the isolation of a cDNA clone (ZSS1) from Z. zerumbet encoding a-humulene synthase, a key enzyme in zerumbone biosynthesis. This recombinant enzyme on expression in Escherichia coli catalysed the formation the caryophyllenes a-humulene (95%) and b-caryophyllene (5%).…”

The Oxygenated Sesquiterpenoid Fraction of Hops in Relation to the Spicy Hop Character of Beer

“…Identification of marker components, i.e. myrcene, linalool, β-caryophyllene, α-humulene, caryophyllene epoxide, humulene epoxide I, humulene epoxide II, and humulenol II, is based on comparison with published data 4,10,18,29 . Clearly, the combined SFE/ SPE methodology furnishes a sharply defined hop oil fraction only consisting of sesquiterpenoids.…”

“…While there is general agreement on the nature of particular compounds associated with floral and citrus scents, the spicy or herbal aspects of hop character are ill defined. Mainly monoterpene alcohols including linalool, geraniol, and citronellol are key elements of the floral and citrus bouquet of hop aroma 6,[8][9][10]14,[17][18][19] . In addition, several esters of linalool and geraniol, and some uncommon cyclic ethers, such as karahana ether, are often mentioned as contributors to a floral hop aroma in beer.…”

“…Oxygenated hop sesquiterpenes, in particular humulene epoxides, have been related to a spicy character 10,[18][19][20] . Although this view is largely accepted in the brewing world, the flavour threshold values of hitherto identified oxygenated sesquiterpenes are generally much higher than their estimated levels in beer 4,8 .…”

The Contribution of Geraniol Metabolism to the Citrus Flavour of Beer: Synergy of Geraniol and β-Citronellol Under Coexistence with Excess Linalool

“…In the field of beer flavour chemistry, several researchers have proposed that geraniol is biotransformed to β-citronellol during fermentation 13,20 . Recently, King and Dickinson 8,9 reported the biotransformation of monoterpene alcohols by yeast metabolism.…”