Dry Hopping Research Articles

Investigations on the Impact of the Special Flavor Hop Variety Huell Melon on the Odor-Active Compounds in Late Hopped and Dry Hopped Beers.

Bottom-fermented and top-fermented beers, both either late or dry hopped with Huell Melon hops, and respective reference beers without late or dry hopping were subjected to a comparative odorant screening by aroma extract dilution analyses. On the basis of differences in the FD factors, 14 odorants were identified as hop-derived. Among them were ethyl 2-methylpropanoate, methyl 2-methylbutanoate, ethyl 2-methylbutanoate, propyl 2-methylbutanoate, myrcene, linalool, and geraniol. Differences between late hopped, dry hopped, and reference beers were substantiated by quantitation. Results showed minimal transfer of myrcene from hops into beer. Moderate transfer was observed for propyl 2-methylbutanoate, geraniol, and linalool. Process-induced changes of ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, and methyl 2-methylbutanoate were beyond a direct transfer from hops into beer, suggesting a formation from the corresponding hop-derived carboxylic acids by yeast. Spiking experiments revealed that linalool and propyl 2-methylbutanoate contributed particularly to the characteristic aroma of beers flavored with Huell Melon hops.

Review: dry hopping in brewing

Dry hopping defined as the addition of hops or hops-products at the cold stage of the brewing process. The practice of dry hopping is currently used in many American styles of beer (IPA, APA, Imperial Stout), Belgian (Ali and Tripoli), traditional British (IPA, Extra Special Bitter), as well as other styles of beer with a developed aromatic component. The main volatile bitter and aromatic components of hops include terpenes (myrcene, humulene and betacarotene), which are characterized by “herbaceous” aroma. There are also linalool and geraniol, which give floral and fruity notes. Terpineol and pinene are making a resinous character. Currently developed special technology, the introduction of hops and the appropriate equipment for dry hopping: flower hops; hop suspension; hop pellets; semi-automatic methods. Dry hopping carried out to increase the “hoppy” aroma of beer and found application due to the increased popularity of small brewing in the world. Since dry hopping performed at relatively low temperatures thermal decomposition and volatilization of aromatic compounds is significantly reduced. This results in a higher concentration of these compounds in the finished product. The source of the aromatic properties of the beer is the polyphenols. In the process of dry hopping about 80-90% of polyphenols extracted during the first 12 hours. Flavan-3-ols increases perceived bitterness and astringency. Monomers and oligomers of flavan-3-ol play a role in the stability of taste, colloidal stability and foam resistance of the drink, have antiradical and antioxidant properties.

Why Humulinones are Key Bitter Constituents Only After Dry Hopping: Comparison With Other Belgian Styles

Although long renowned worldwide for its unique dry-hopped (DH) Trappist beer, Belgium did not develop this process for other brands until the last decade. Twenty-one commercial Belgian DH beers were investigated and compared with a few other typical Belgian beers whose production involves either late hopping or aged hop addition (Gueuze). Bitterness was determined by spectrophotometric measurements (isooctane extraction) and by reversed phase high performance liquid chromatographic with UV detector (RP-HPLC-UV) (simultaneous quantitation of humulones, cis-/trans-isohumulones, reduced isohumulones, humulinones, and hulupones). In dry-hopped Belgian beers, humulinones (found at concentrations up to 13.3 mg/L) were estimated to be responsible for up to 28% of their bitterness. As humulinones revealed to be gradually lost through boiling (22%), clarification (5%), and fermentation (14%), non-dry-hopped (NDH) beers often displayed levels below 1.7 mg/L. Even in Gueuze beers for which old, humulinone-containing hops are used, no humulinone was found. Contrary to humulones, which were detected up to 7.2 mg/L in DH beers, hulupones were found at less than 3 mg/L in all Belgian beer styles. Humulinones were not produced in the boiling wort from humulones (in contrast to hulupones, readily synthesized from lupulones) but were significantly solubilized from hop thanks to their hydrophilicity. Yet, while the co-form accounted for about 50% of the humulones, the n-form prevailed for humulinones. Some humulinone degradation products were evidenced by RP-HPLC-MS/MS, and as suggested by their retention time (RT), should be more polar than their precursors. Bottle refermentation emerged as an additional critical step of humulinone loss, explaining the low levels found even in some strongly DH beers.

Investigations into the Transfer Rate of Volatile Compounds in Dry Hopping Using an Octanol-Water Partition Coefficient Model

ABSTRACTDry hopping is a powerful practice for imparting a multitude of flavors into beer. In this study, the influence of ethanol content, temperature, dosage, and hop variety on the transfer of essential oil during dry hopping was examined on a laboratory scale. The dry hopping was performed with nonalcoholic beer and beer containing 5.0 and 8.1% ethanol at 1 and 20°C using the hop varieties Tettnanger, Cascade, Hallertau Blanc, and Eureka. The results showed that the basic beer, hop variety, and dry hopping regime influence the composition of hop essential oil constituents in dry-hopped beer. The increase of the basic beer ethanol content, and especially the rise in temperature, led to a significant increase in the proportion of monoterpenes such as β-myrcene among hop volatiles in dry-hopped beers. Increasing hop dosage led to higher proportions of alcoholic compounds (linalool). Furthermore, the transfer rates of particular volatile hop-derived substances correlated with their octanol-water partition coefficients (log KOW), which is a measure of the hydrophobicity of a compound, regardless of tested factors in dry hopping. Therefore, it is proposed that the log KOW could be a useful model for the prediction of transfer rates of hop oil flavor components in dry hopping. However, the transfer rates of the alcohols linalool, geraniol, α-terpineol, and 1-octen-3-ol were higher than the expected levels from the log KOW values. These compounds are reported present in bound form in hops and released during dry hopping.

Analytical and sensory profiles of Slovenian and Czech hop genotypes in single hopped beers

The sensory profile of beer is influenced by the hop variety and hopping technology. This study examined pilot (50 L) pale lager beers, hopped in the kettle with (or without) single dry hopping. Seven Slovenian, four Czech and one American genotypes were used to determine the impact of dry hopping on the sensory and volatile profiles of beer. Descriptive and bitterness lingering assessment sensory methods were used. The essential oil composition of the hops and beers was accessed using GC/MS so as to clarify their correlation to sensory profiles of both brewing processes. Changes in essential oils and aroma profiles of beer related to storage were evaluated. Results showed differences among the genotypes in the hop oil profiles in the kettle-hopped beers. Based on the hop dose, dry hopping increased the monoterpene alcohol (r = 0.60) and monoterpene hydrocarbon (r = 0.74) content. Hoppy flavour correlated to the monoterpene alcohols and hydrocarbons. Hop-derived aroma profiles of the genotypes differed. Dry-hopped beers tended to have a more bitter aftertaste than solely kettle-hopped beers. Both kettle and dry hopped beers of all genotypes showed good sensory acceptance (3–4.5; nine-point scale). After storage of beer, the content of most essential oils and hoppy flavour significantly decreased. The sensory aging of the kettle and dry-hopped beers was comparable. Copyright © 2018 The Institute of Brewing & Distilling

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 μg/L, respectively, for a threshold of 8 μg/L for linalool and 4 μg/L for geraniol). β-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 β-glucosidase releases octan-1-ol, used here as an internal standard, 2.8 times more efficiently than geraniol. β-Glucosidase treatment caused the release of linalool, α-terpineol, β-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.

Contributions of Select Hopping Regimes to the Terpenoid Content and Hop Aroma Profile of Ale and Lager Beers

Recently, brewers have dramatically increased the complexity and intensity of aromas in hop-forward beers by using diverse hopping regimes. For this study, the terpenoid content and sensory attributes of beers made using different hop additions were measured. Beers were brewed while varying two factors: hop cultivar (Simcoe and Hallertau Mittelfrüh) and timing of hop addition (60 min boil, 25 min whirlpool, or 48 h dry hopping). Additionally, the impact of yeast strain on treatment was investigated. Each treatment was compared with an unhopped control using stir-bar sorptive extraction GC-MS and descriptive sensory analysis. Multivariate statistical analysis showed relationships between instrumental and sensory techniques. Whirlpool additions produced beers with the highest concentrations of geraniol, linalool, and β-citronellol; beers brewed with highly aromatic Simcoe hops produced more intense and individually distinct aromas for each hopping regime compared with the Hallertau Mittelfrüh hopped beers. Conversely, beers brewed with Hallertau Mittelfrüh hops showed less intense aromas with less distinction between hopping regimes, except for the dry-hopped treatment, which was characterized by a more floral type of aroma than the other Hallertau Mittelfrüh treatments. This research shows that despite the popularity of dry hopping as an aroma hopping method, whirlpool additions can produce more intensely aromatic beers.

Scale‐up of Dry Hopping Trials: Importance of Scale for Aroma and Taste Perceptions

AbstractIn this study beers that were dry hopped in three different batch sizes were compared. The hop‐oil concentrations were measured and possible aroma‐active hop volatiles were identified in the hop pellets as well as in the beers. The analytical results were correlated with the tasting results from a trained tasting panel. Mass transfer rates were not comparable between the different scales, and significant differences could be detected by the tasters. The beers dry hopped on an industrial scale are not comparable in flavor and odor to those dry hopped on a laboratory scale.

Influence of Hop Oil Content and Composition on Hop Aroma Intensity in Dry-Hopped Beer

When hops are added to beer, varying degrees of hoppy aroma persist as a result of cultivar differences and the point of hop addition. Dry hopping is a technique whereby hops are added to beer to leverage the maximum aroma potential of the hop oil. Given that hop oil serves as the primary reservoir of aromatic compounds in the hops, we hypothesized that using hops with greater total oil content (mL/100 g) will result in higher levels of hoppiness for dry-hopped beers. An unhopped beer was dry hopped with 23 individual Cascade hop lots, and the resultant beer was evaluated with sensory descriptive analysis. The results demonstrated a negligible role of total oil content (mL/100 g) as an indicator of hoppiness. In fact, there was no correlation between total oil content and overall hop aroma intensity. Therefore, the specific volume of hop oil is an inadequate indicator of hoppiness potential in the dry-hop system. This work challenges several conventional ideas, namely, that using hops with higher oil content for dry hopping promotes a greater degree of hoppy aroma in beer. This research affirms the complexity of how hop materials relate to sensory aroma performance in beer systems.

Manganese in Brewing Raw Materials, Disposition during the Brewing Process, and Impact on the Flavor Instability of Beer

Like iron and copper, manganese promotes the staling of beer, by converting ground state oxygen to reactive oxygen species. Manganese was detected in beers at levels that are likely to impact the aging of beer. Manganese originates in the grist materials but is present at even higher levels in hops. Although there is substantially more iron in those hops than manganese, the delivery into beer of these ions is much greater for manganese. Leaching of manganese into beer is much higher than in the equivalent quantity of deionized water. This study suggests that further study is warranted into the adverse impact of dry hopping on the flavor stability of beers.

Are Humulus lupulus L. ecotypes and cultivars suitable for the cultivation of aromatic hop in Italy? A phytochemical approach

Breeding programs are increasingly interested in the introduction of traits from wild hops and in the detection of the cultivars most suitable under different climatic conditions. Eleven Humulus lupulus ecotypes were selected from distinct populations in Northern Italy, grown in a collection field and evaluated for their yield and cone aromatic profiles after a three-year acclimatization. At the same time, the performance of 10 H. lupulus cultivars (Bramling Cross, Cascade, Challenger, Fuggle, Magnum, Marynka, Nugget, Target, Tettnanger, Willamette) grown under the same conditions was investigated by comparing them to commercially available material. Estimated gross yield for ecotypes ranged between 636 and 2491kg/ha, largely exceeding hop production for commercial cultivars (277–1442kg/ha), while essential oil accumulation was inverted. Essential oils obtained from mature cones were characterized by GC–MS. In the volatile fraction of most ecotypes, selinene isomers were extremely abundant and myrcene was low, while α–humulene/β–caryophyllene ratio was comprised between 0.15 (Pasqui 1) and 1.68 (Tavernelle and Roggino 2). The phytochemical variability among the genetic pool screened suggests its potential use for breeding and improvement of cultivated varieties, in particular for plant material aimed to be used in the dry hopping stage of brewing. Northern Italy seem to be particularly suitable for the cultivation of finishing, aromatic hops like Bramling Cross, Magnum, Marynka and Tettnanger.

Beer metabolomics: molecular details of the brewing process and the differential effects of late and dry hopping on yeast purine metabolism

The flavour of beer is complex, based upon changes at the molecular level in the key raw materials, notably grain, hops and yeast, as well as during the process stages that comprise malting and brewing. As analytical techniques evolve in their sophistication and sensitivity, there are opportunities to delve ever more deeply into the fate of small molecules in brewing. To this end, 1H nuclear magnetic resonance (NMR) metabolomics was used to follow the progression of 76 metabolites in four different late or dry hopped beers (brewed in triplicate) at five time points throughout the brewing process. The majority of the metabolites identified, including sugars, amino acids and nucleotides, significantly decreased in concentration from the start of the boil to post-secondary fermentation, whereas energy-related and fatty acid associated metabolites significantly increased in concentration as wort nutrients were consumed by the yeast. Adenine was significantly higher in the dry hopped brews than in the late hopped brews after both primary (p = 2.1 × 10−6) and secondary (p = 2.7 × 10−9) fermentation, while 2′-deoxyadenosine (after primary, p = 1.1 × 10−2, after secondary, p = 3.2 × 10−5) and adenosine (after primary, p = 2.6 × 10−8; after secondary, p = 3.1 × 10−7)were significantly lower in the dry hopped beers at these time points. These results give molecular insight into the brewing process and the differential effects of hopping methods on yeast purine metabolism. Copyright © 2015 The Institute of Brewing & Distilling

Dry Hopping on a Small Scale: Considerations for Achieving Reproducibility

Dry Hopping on a Small Scale: Considerations for Achieving Reproducibility

Dry Hopping and Its Effects on the International Bitterness Unit Test and Beer Bitterness

Dry Hopping and Its Effects on the International Bitterness Unit Test and Beer Bitterness

Italian hop germplasm: Characterization of wild Humulus lupulus L. genotypes from Northern Italy by means of phytochemical, morphological traits and multivariate data analysis

To evaluate the intraspecific diversity of wild Humulus lupulus in Northern Italy, 22 hop accessions were collected from distinct populations. The selected germplasm was genetically probed with 9 SSR primers, grown in a collection field and compared with 5 commercial varieties (Columbus, Fuggle, H. Magnum, Tettnanger, Willamette) cultivated under the same conditions. Hops were evaluated for their aromatic profile, xanthohumol and bitter acids composition by means of GC–MS and HPLC-UV, and further analyzed by principal component and cluster analysis. A great phytochemical diversity was found and wild populations were classified in three distinct clusters in terms of volatile composition and in two separate groups in terms of bitter substances content. Multivariate data analyses revealed that selinenes, α-acids, trans-β-farnesene and α-caryophyllene/β-humulene ratio, both contribute the most to the classification of Italian genotypes. Xanthohumol and α-acids content were higher than previously reported for European wild hops. Total α- and β-acid content ranged between 2.98g/100g (Busseto 13) and 11.11g/100g (Rio Gambero). In the volatile fraction, selinene isomers were above 40% in the essential oils isolated from 6 samples; myrcene ranged between 0.5 (Pasqui 1) and 30% (ET8), while α-humulene/β-caryophyllene ratio was comprised between 0.26 (ET8) and 4.16 (Roggino 2). The phytochemical variability and the presence of traits valuable for brewing suggest the potential exploitation of some ecotypes for breeding and improvement of the cultivated varieties, in particular for plant material aimed to be used in the dry hopping stage of brewing. Some wild genotypes may be valuable as dual purpose or aromatic hops, with properties similar to Fuggle and Tettnanger. The results of the first comparative report of commercial H. lupulus cultivars in Italy are also reported.

Possibilities to improve the antioxidative capacity of beer by optimized hopping regimes

Different hopping regimes were evaluated to investigate the effect on the oxidative stability of wort and beer. Compared with a single hop dosage at the beginning of wort boil, it was possible to increase the concentration of α-acids in pitching wort and beer by applying incremental hop dosage, dry hopping or the use of a pre-isomerized hop product in combination with an α-acid extract, which concomitantly resulted in lower iron concentrations and an enhanced flavour stability as indicated by standard wort and beer analyses, atomic absorption spectroscopy, electron spin resonance spectroscopy and sensory analysis of fresh and force-aged beers. The functional principle of hop dosage variations is explained by saving of α-acids throughout the wort production process, which yields an increased formation and precipitation of pro-oxidative acting transition metal ions (e.g. Fe) in α-acid-complexes during the whirlpool rest and fermentation. Consequently, fewer reactive oxygen species are generated. Additional laboratory trials simulating wort cooling and beer storage in buffered model solutions proved that un-isomerized α-acids are strong iron chelators and confirmed the functional principle of the applied hopping regimes. Negative effects of higher α-acid contents on fermentation performance and depletion of the zinc concentration, which is an essential nutrient for yeast, could be excluded. Copyright © 2014 The Institute of Brewing & Distilling

American India Pale Ale matrix rich in xanthohumol is potent in suppressing proliferation and elevating apoptosis of human colon cancer cells

SummaryAmerican India Pale Ales (IPAs) with and without addition of dark/roasted malts (DRM) and dry hopping (DP) were analysed to determine whether these processes will increase total phenolic content (TP), antioxidant capacity (AA) and the levels of bioactive compounds (xanthohumol, XN and isoxanthohumol, IX). In addition, bioactivity of whole beer matrices, that is, the ‘phytochemical team approach,’ was compared to isolated compounds, the ‘silver bullet approach,’ by measuring antiproliferative and pro‐apoptotic properties using HCT 116 human colon cancer cells. DP and addition of DRM elevated the XN, IX, TP and AA. Dark malts reduced losses in XN and TP due to filtration. Xanthohumol content positively correlated with phenolic content (r = 0.88, P = 0.0002), indicating that the processes which increased xanthohumol content also elevated other bioactive compounds in beer. However, whole extract from IPAs were more potent in suppressing proliferation and elevating apoptosis in colon cancer cells compared with xanthohumol alone.

Sensory Descriptive Analysis and Free-Choice Profiling of Thirteen Hop Varieties as Whole Cones and After Dry Hopping of Beer

Sensory descriptive analysis and free choice profiling have been applied to the characterization of aroma in thirteen hop varieties, both in the whole cone form and after the hops had been used to dry hop beer. 180 terms were identified and used for the classification of hops. Only two of the varieties displayed closely similar profiles. Varieties could, however, be broadly grouped into those with overriding citrus notes and those with substantial green tea, hay and wet wood nature. Dry hopping tends to compress varieties when evaluated for aroma, perhaps indicating a degree of masking by other beer components. However the aroma notes detected are similar whether assessed in whole cones or in beers.

How the Method of Beer Dispense Influences the Served CO2 Content and the Sensory Profile of Beer

The influence of the hopping method (boiling stage hopping or dry hopping), the fermentation temperature (12 and 18 °C), and the yeast strain (five different yeasts) on the physical-chemical characteristics (bitterness, color, alcohol content), the phenolic content, the volatile compounds, as well as the sensory profile of beers, has been studied. The hopping method was much more influential than temperature and yeast strain, however, its influence on volatile content clearly depended on the fermentation temperature, with a higher content of volatile compounds, when a higher fermentation temperature was employed. For phenolic compounds, dry hopping produced less polyphenol-rich beers, regardless of the fermentation temperature. Sensorily, it resulted in more floral and fruity beers than those produced by boiling stage hopping, which exhibited a more intense toasted aroma. Concerning yeast strain, no relationship could be established between the type of commercial yeast (bottom or top-fermenting) and the resulting volatile content.

Sensory Descriptive Analysis and Free-Choice Profiling of Thirteen Hop Varieties as Whole Cones and after Dry Hopping of Beer

Sensory descriptive analysis and free choice profiling have been applied to the characterization of aroma in thirteen hop varieties, both in the whole cone form and after the hops had been used to dry hop beer. 180 terms were identified and used for the classification of hops. Only two of the varieties displayed closely similar profiles. Varieties could, however, be broadly grouped into those with overriding citrus notes and those with substantial green tea, hay and wet wood nature. Dry hopping tends to compress varieties when evaluated for aroma, perhaps indicating a degree of masking by other beer components. However the aroma notes detected are similar whether assessed in whole cones or in beers.