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The essential oil of hops — A Review

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Abstract

The composition of essential oil of hops is reviewed and the nature of hop oil components which survive into wort and beer is discussed. Methods which are available to the brewer for imparting hop character to beer are critically evaluated.

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... To date, reviews published in the area of hops have focused on the chemical composition of hop oil, the transfer of hop derived volatiles into the final beer as a result of different hopping techniques, hop oil analysis techniques and the odour characteristics of single hop oil compounds (Almaguer, Schönberger, Gastl, Arendt, & Becker, 2014;Eyres & Dufour, 2009;Sharpe & Laws, 1981;Van Opstaele et al., 2006). ...
... Instead, they play an important role as precursor compounds that are transformed into oxidation products, thereby adding to 'noble hop' or 'kettle hop' aroma and flavour of beer (Naya & Kotake, 1972). For instance, it has been suggested that boiling β-myrcene in water in the presence of oxygen, might result in the formation of perillene, a compound that induces citrusy/lemony aroma notes (Dieckmann & Palamand, 1974;Sharpe & Laws, 1981;Van Opstaele, De Causmaecker, Aerts, & De Cooman, 2012), as well as to linalool and geraniol, two of the most impactful odourants derived from hop essential oil (Forster & Gahr, 2013). ...
... When dry hopping beer, some compounds of the hydrocarbon fraction, including myrcene, humulene and caryophyllene, have been observed to survive the brewing process at reduced levels. Myrcene, the dominant monoterpene in the hydrocarbon fraction accounts for up to 75% of total hop oil (Sharpe & Laws, 1981; Thompson, Marriott, Dowle, & Grogan, 2010). However, βmyrcene was found to be adsorbed to the non-polar surface of yeast cells or to be transported to the surface of the fermenting beer by carbon dioxide bubbles and stripped with the fermentation gases. ...
Article
Considering the substantial amount of research that has been published in the field of hop science during the last decades, very little is known with regard to the multimodal flavour perception of hop-derived volatiles that not only contribute to the pleasant ‘hoppy’ aroma and flavour, but are also involved in other sensations of gustatory and trigeminal origin perceived in beer. The aim of this research was to further understand the sensory complexity of Magnum hop essential oil and scCO2 hop oil fractions extracted therefrom. This PhD project combined static and dynamic sensory techniques, an established gas chromatographic method, and comprehensive statistical analyses to investigate the relationship between hop volatile compounds and their sensory characteristics (quantitative and qualitative) in different matrices. The olfactory, gustatory and trigeminal differences between five hop oil fractions representing the main chemical classes of Magnum hop oil were determined in a simple model solution (4% ABV) using a newly established attribute lexicon and following a Quantitative Descriptive Analysis (QDA) approach. The fractions induced a range of different aroma and flavour sensations, which could partly be attributed to specific hop aroma compounds. The most polar compounds in the terpene alcohol fraction were suggested to be responsible for cross-modal interactions eliciting both aroma and/or taste and trigeminal sensations. A peppery tingling mouthfeel was perceived, which is assumed to be a sensation innervated by the trigeminal nerve. The terpene alcohol fraction was further categorised into monoterpene alcohols (i.a. geraniol, linalool) assumed to be mainly responsible for olfactory sensations and sesquiterpene alcohols (i.a. humulol, humulenol II) to foremost induce gustatory and tactile sensations. Further fractionation specifically targeting single compounds and compound groups (sub-fractions) that were added to a commercial lager beer base (4.5% ABV) to measure the impact of perceptual interactions between compounds and the beer matrix using a revised attribute lexicon and adjusted dosage rates. A clear cause-effect-relationship could be located between geraniol and the sweet taste perceived in the beer. Geraniol also induced a smooth bitterness, which was opposed by the harsh bitterness quality added by sesquiterpene hydrocarbons. Linalool was classified as a aroma/flavour ‘enhancer’ rather than individually contributing to the sensory profile. Significant effects on lingering mouthfeel sensations remained absent, which illustrated the need for temporal sensory assessments to adequately and holistically discriminate the samples with regard to these sensations. A Temporal Check-All-That-Apply (TCATA) by modality approach was used to assess multiple sensory characteristics of selected hop flavour products perceived simultaneously. The products contained the previously studied hop oil fractions and were combined with either iso-alpha-acids or oxidised beta acids (hulupones) in a lager base beer brewed without any hop materials. Bitter acid extracts were found to significantly affect the duration and sensory profiles of the hop flavour products in the beer suggesting a sensory interaction induced by the co-occurrence of hop aroma compounds and hop bitter stimuli. Lingering sensations (peppery tingling, astringency) were foremost found to significantly discriminate between the samples at the end of the evaluation period (>2min). Since temporal sensory data is inherently noisy, a part of this research included the examination of TCATA data pre-processing approaches using comprehensive statistical analyses. This revealed that time standardising the TCATA by modality data could not remove inter- and intra-individual variation between the panellists and thus, not improved the quality of the sensory data. This research has provided new and in-depth knowledge on the sensory properties of scCO2 hop oil fractions, sub- fractions, and key compounds extracted from Magnum hop. Moreover, different sensory characterisation strategies and tools are presented that captured the fine nuances of the sensory profiles of these hop extracts. The findings demonstrated the involvement of hop volatile compounds in sensory interaction effects causing multi-modal profiles in beer. Their ability to modify gustatory and trigeminal sensations should be considered for future developments of flavour preparations.
... The main terpenes found are the monoterpene β-myrcene and the sesquiterpenes β-caryophyllene and αhumulene [18]. The second group are oxygen-containing compounds representing around 30% of the total oil [19][20][21] and the third group, the thioesters, sulphides and other sulphur-containing compounds, are found only in traces [20][21][22][23][24]. Those compounds can be divided into groups based on the type of aroma they provide, such as citrus, herbal, floral, fruity or a typical hoppy aroma. ...
... The main terpenes found are the monoterpene β-myrcene and the sesquiterpenes β-caryophyllene and αhumulene [18]. The second group are oxygen-containing compounds representing around 30% of the total oil [19][20][21] and the third group, the thioesters, sulphides and other sulphur-containing compounds, are found only in traces [20][21][22][23][24]. Those compounds can be divided into groups based on the type of aroma they provide, such as citrus, herbal, floral, fruity or a typical hoppy aroma. ...
... The main terpenes found are the monoterpene β-myrcene and the sesquiterpenes β-caryophyllene and α-humulene [18]. The second group are oxygen-containing compounds representing around 30% of the total oil [19][20][21] and the third group, the thioesters, sulphides and other sulphur-containing compounds, are found only in traces [20][21][22][23][24]. Those compounds can be divided into groups based on the type of aroma they provide, such as citrus, herbal, floral, fruity or a typical hoppy aroma. ...
Article
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This study evaluates the content of essential oils (EOs) and prenylated flavonoid Xanthohumol (XN) in extracts of Slovenian hops, cultivar Aurora, obtained by using fluids of different polarity. It is a continuation of our previous work, investigating the extraction of bitter acids from hops. Extraction was conducted semi-continuously, using sub- and supercritical fluids of different polarity, i.e., carbon dioxide (CO2) and propane as non-polar and dimethyl ether (DME) as the polar solvent. The experiments explored a temperature range between 20 °C and 80 °C and pressures ranging from 50 bar to 150 bar. The content of XN in extracts was analysed using high-performance liquid chromatography and experiments demonstrated the largest concentration of XN was obtained using DME. In order to analyse the EO components in extracts, connected with a distinct odour, the steam distillation of extracts was performed and GC analysis was employed. Hop oil derived from CO2 extracts at specific conditions, had the highest relative concentration of linalool, β-caryophyllene and α-humulene, and oil derived from propane extracts had the highest content of all other five selected components (myrcene, geraniol, farnesene, α-selinene and δ-cadinene). The relative content of the investigated EO components in DME extracts was similar to that in propane extracts.
... The second main group, which accounts for around 30% of the total oil content, are oxygen-containing compounds. [5,19,20] A third group -the sulfur-containing compounds -is found only in trace amounts. [19][20][21] The biosynthesis of HEO takes place in the lupulin glands and occurs more slowly than the biosynthesis of resins. ...
... [5,19,20] A third group -the sulfur-containing compounds -is found only in trace amounts. [19][20][21] The biosynthesis of HEO takes place in the lupulin glands and occurs more slowly than the biosynthesis of resins. Consequently, HEO is only fully developed late in the hop ripening phase. ...
... [30,31] These compounds can be sorted into three groups: aliphatic compounds, monoterpenes, and sesquiterpenes. [19] The aliphatic fraction is a minor one and its representatives are only found in low concentrations. Monoterpenes are further divided into acyclic, monocyclic, and bicyclic types. ...
Article
Hop cones (Humulus lupulus L.), or more specifically the lupulin glands, hold the reason for the specific, pleasant aroma of hops – its essential oil. The hops themselves, or the extracted oil, are used almost exclusively in beer production. The essential oil is an indispensable part of beer and is responsible for its characteristic aroma. However, hop essential oil (HEO) also has a broad range of positive effects on human health and is a potential natural pesticide that has no harmful impacts on humans. This review summarizes basic information about HEO, including its chemical composition and methods for extraction and analysis, while also providing a comprehensive overview of the contribution to beer aroma, health, and insecticide applications for this versatile essential oil.
... To date, reviews published in the area of hops have focused on the chemical composition of hop oil, the transfer of hop derived volatiles into the final beer as a result of different hopping techniques, hop oil analysis techniques and the odour characteristics of single hop oil compounds (6,(15)(16)(17). Recently, Rettberg et al. ...
... Instead, they play an important role as precursor compounds that are transformed into oxidation products, thereby adding to 'noble hop' or 'kettle hop' aroma and flavour of beer (74). For instance, it has been suggested that boiling β-myrcene in water in the presence of oxygen, might result in the formation of perillene, a compound that induces citrusy/lemony aroma notes (15,75,76), as well as to linalool and geraniol, two of the most impactful odourants derived from hop essential oil (77). ...
... When dry hopping beer, some compounds of the hydrocarbon fraction, including myrcene, humulene and caryophyllene, have been observed to survive the brewing process at reduced levels. Myrcene, the dominant monoterpene in the hydrocarbon fraction accounts for up to 75% of total hop oil (15,78). However, βmyrcene was found to be adsorbed to the non-polar surface of yeast cells or to be transported to the surface of the fermenting beer by carbon dioxide bubbles and stripped with the fermentation gases. ...
Article
Full-text available
Hops are a key ingredient to add bitterness, aroma and flavour to beer, one of the most consumed beverages worldwide. Essential oils from different hop varieties are characterised by similar classes of chemical compounds and complexity, but their contribution to sensory characteristics in beer differs considerably. Volatiles in hop oil are categorised into several chemical classes. These induce diverse aroma and flavour sensations in beer being described as 'floral', 'fruity' (e.g. contributed by alcohols, esters, sulphur-containing compounds), 'spicy', 'woody', 'herbal' (sesquiterpenes, oxygenated sesquiterpenoids), and 'green' (alde-hydes). The perception of hop volatiles depends on their concentrations and combinations, but also on threshold levels in different beer matrices or model systems. Several studies attributed modified taste and mouthfeel sensations to the presence of hop volatiles contributing to a multisensory perception of hop flavour. Linalool is frequently observed to show additive and synergistic-type behaviour and to affect aroma perception if combined with geraniol. Linalool has also been found to be involved in aroma-taste interactions, modifying the perception of bitterness qualities in beer. Particularly oxygenated sesquiterpenoids are suggested to be responsible for an irritating, tingling sensation indicating the activation of trigeminal receptors. The majority of these sensory interactions have been discovered almost by accident and a systematic research approach is required to gain a broad understanding of these complex phenomena. This review provides an overview of factors affecting the perception of hop derived volatiles involved in different sensory characteristics of beer, while illustrating the latest advances and highlighting research gaps from a sensory science perspective.
... Furthermore, the hop storage index (HSI) based on UV/Vis spectroscopy was established according to EBC 7.13 as a reference value for hop aging. Storage tests demonstrated that the bitter acid content decreases steadily and the composition of the essential oils changes due to oxidation reactions, but the deterioration process can be reduced significantly by inert storage conditions at low temperatures [11][12][13]. As HSI, the ratio of the absorption at 275 nm, which is characteristic for the oxidation products of bitter acids, and at 325 nm, which is characteristic for the fresh bitter acids, is calculated [1,12]. ...
... Multivariate data analysis has already been applied in the quality control of hop, mostly for authenticity control [14,15]. Ocvirk et al. used multivariate cluster analysis (CA) for the varietal classification of five different hop varieties concerning the bitter acid and essential oil composition [14] that are known to be characteristic for each hop cultivar [12,13,16]. Kovačevič et al. also used GC-FID combined with principal component analysis (PCA) and CA for the verification of hop varieties [15]. ...
... Here, the complementary separation of GC and IMS allows distinguishing these compounds from the terpene signals, because their DT clearly differs. These signals belong to minor volatile components of hops, such as ketones, aldehydes, carboxylic acids, and esters of different chain length and branch type [1,2,9,13], which are reported to be byproducts from terpene biosynthesis and from degradation processes of lipids and bitter acids [2]. An exemplary set of substances was identified as 2-butanone (8), 2heptanone (9), and 2-nonanone (10) via reference standards in the GC-IMS data. ...
Article
Full-text available
For the first time, a prototype HS-GC-MS-IMS dual-detection system is presented for the analysis of volatile organic compounds (VOCs) in fields of quality control of brewing hop. With a soft ionization and drift time-based ion separation in IMS and a hard ionization and m/z-based separation in MS, substance identification in the case of co-elution was improved, substantially. Machine learning tools were used for a non-targeted screening of the complex VOC profiles of 65 different hop samples for similarity search by principal component analysis (PCA) followed by hierarchical cluster analysis (HCA). Partial least square regression (PLSR) was applied to investigate the observed correlation between the volatile profile and the α-acid content of hops and resulted in a standard error of prediction of only 1.04% α-acid. This promising volatilomic approach shows clearly the potential of HS-GC-MS-IMS in combination with machine learning for the enhancement of future quality assurance of hops. Graphical abstract
... V roce 1980 byly chmelové silice kategorizovány do tří základních frakcí: uhlovodíkové, kyslíkaté a frakci sirných sloučenin (Sharpe a Laws, 1981). Největší zastoupení ve chmelu a zároveň také nejvyšší prahové koncentrace senzorického vnímání vykazují látky patřící do první zmíněné frakce (Schonberger a Kostelecky, 2011). ...
... In 1980, the hop essential oils were categorized into three basic fractions: hydrocarbon, oxidized and sulphur fractions (Sharpe and Laws, 1981). Compounds from the hydrocarbon fraction are present in the highest concentrations in hops and also have the highest sensory threshold values (Schonberger and Kostelecky, 2011). ...
... This fraction counts for 50 to 80 % of the total content of essential oils in hops (Briggs, 2004). It consists mainly of aliphatic hydrocarbons, monoterpenes and sesquiterpenes (Sharpe and Laws, 1981). A part of them already oxidize to the oxygen fraction during the cultivation and the hop processing and further during the production and storage of beer (Eyres and Dufour, 2008;Almaguer et al., 2014). ...
Article
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Dry hopped beers gain their characteristic flavour from hop products purposely added during the cold stage of production. Although the production of these beers has not so broad a tradition in the Czech Republic as for instant in Great Britain or the United States, their popularity increases every year. This study provides a complete set of theoretical and practical information about the production of dry hopped beers. The relevant sensory active compounds of hops creating the characteristic beer aroma and factors influencing their transfer into beer are introduced. The last part of the study deals with some important risk factors which must be considered during the production of dry hopped beers.
... Monoterpenes are predominantly represented by b-myrcene (4) with up 57.9% (Tables 1 and 3). However, a diversity of minority non-oxygenated terpenes can be encountered in the essential oil of various cultivars, including alcohols, aldehydes, acids, ketones or esters (Sharpe and Laws 1981;Bernotien_ e et al. 2004;Nance and Setzer 2011;Aberl and Coelhan 2012;Praet et al. Lammens and Verzele (1968), Katsiotis et al. (1989), Malizia et al. (1999), Bernotiene et al. (2004, Nance andSetzer (2011), Van Opstaele et al. (2013), Akdemir (2015) and Praet et al. (2015) 5 b-Ocimene tr-1 Hartley (1968), Lammens and Verzele (1968), Katsiotis et al. (1989), Bernotiene et al. (2004), Nance and Setzer (2011) and Praet et al. (2015) 6 a-Phellandrene 0.01-0.14 ...
... a- Praet et al. 2015). Sulfurcontaining compounds, such as 2,3,4-trithiapentane, 2,3,5-trithiahexane and methylthiomethyl-2methylbutanethiolate were also noted in small amounts (Peppard and Sharpe 1977;Moir et al. 1980a, b;Sharpe and Laws 1981). These latter compounds are not listed in an exhaustive manner in this review. ...
... Other terpenoids (Table 5) Some triterpenoids, including a-amyrin (122), bamyrin (123), d-amyrin (124), lupeol (125) and ursa-9(11), 12-dien-3b-ol (126), have been identified in hop' cones (Akazawa et al. 2012). Sharpe and Laws (1981) and Katsiotis et al. (1989) 110 (E)-Nerolidol 0.1-0.3 Sharpe and Laws (1981), Katsiotis et al. (1989) and Nance and Setzer (2011) Naya and Kotake (1969c) Phenolic compounds of hop (Tables 6,7,8,9,10,11,12) Flavonoids and derivatives (Tables 6,7,8,9) Flavonoids are the most diverse and widespread distributed class of phenolic compounds with different metabolic functions within plant. ...
Article
Full-text available
Humulus lupulus L. (Cannabaceae), commonly named hop, is widely grown around the world for its use in the brewing industry. Its female inflorescences (hops) are particularly prized by brewers because they produce some secondary metabolites that confer bitterness, aromas and antiseptic properties to the beer. These sought-after metabolites include terpenes and sesquiterpenes, found in essential oil, but also prenylated phenolic compounds, mainly acylphloroglucinols (bitter acids) from the series of α-acids (humulone derivatives). These metabolites have shown numerous biological activities, including among others, antimicrobial, sedative and estrogenic properties. This review provides an inventory of hop’s chemistry, with an emphasis on the secondary metabolites and their biological activities. These compounds of biological interest are essentially produced in female inflorescences, while other parts of the plant only synthetize low quantities of them. Lastly, our article provides an overview of the research in plant biotechnology that could bring alternatives for hops metabolites production.
... The lupulin glands are part of the female flower also known as hop cones and are fully formed on the hop cones by end of the ripening season. Essential oil content in hops varies from 0.5 to 3 , and losses of essential oil due to resinification and oxidation while in storage even at 0 can reach up to 30 or more depending on duration of storage 15 . ...
... In the early 80 s Sharpe and Laws 15 reviewed the available literature on hops essential oil and classified hop oil components into hydrocarbon components, oxygenated components, and sulfur-containing components. The hy-drocarbons in hop oil were further classified into aliphatic hydrocarbons, monoterpenes subdivided into acyclic myrcene, β-ocimene , monocyclic limonene, ρ-cymene, α-phellandrene, β-phellandrene , and bicyclic α-pinene, β-pinene, and sabinene , and sesquiterpenes subdivided into acyclic farnesene , monocyclic germacrene B, germacrene D, and humulene , bicyclic γ-cadinene, δ-cadinene, α-cadinene , and tricyclic 15 . The monoterpenes α-pinene, β-pinene, myrcene, and limonene and the sesquiterpenes α-humulene, farnesene, caryophyllene, muurolene, and selinene represent up to 80 of total oil 4 . ...
... The oxygenated components, a combination of terpene alcohols, aldehydes, acids, ketones, epoxides, and esters, are approximately 30 of the total oil and are formed during ripening, processing, and storage 4 . Linalool, geraniol, caryophyllene oxide, farnesol, α-terpeniol, carvone are components from the oxygenated fraction among many others 15 . The sulfur-containing fraction, consisting of thioesters, straight chain sulfides, and cyclic terpenoid sulfides, represents only up to 1 of the total oil 15 . ...
Article
The profile and bioactivity of hops (Humulus lupulus L.) essential oil, a complex natural product extracted from cones via steam distillation, depends on genetic and environmental factors, and may also depend on extraction process. We hypothesized that compound mixtures eluted sequentially and captured at different timeframes during the steam distillation process of whole hop cones would have differential chemical and bioactivity profiles. The essential oil was collected sequentially at 8 distillation time (DT) intervals: 0-2, 2-5, 5-10, 10-30, 30-60, 60-120, 120-180, and 180-240 min. The control was a 4-h non-interrupted distillation. Nonlinear regression models described the DT and essential oil compounds relationship. Fractions yielded 0.035 to 0.313% essential oil, while control yielded 1.47%. The oil eluted during the first hour was 83.2%, 9.6% during the second hour, and only 7.2% during the second half of the distillation. Essential oil (EO) fractions had different chemical profile. Monoterpenes were eluted early, while sequiterpenes were eluted late. Myrcene and linalool were the highest in 0-2 min fraction, β-caryophyllene, β-copaene, β-farnesene, and α-humulene were highest in fractions from middle of distillation, whereas α- bergamotene, γ-muurolene, β- and α-selinene, γ- and δ-cadinene, caryophyllene oxide, humulne epoxide II, τ-cadinol, and 6-pentadecen-2-one were highest in 120-180 or 180-240 min fractions. The Gram-negative Escherichia coli was strongly inhibited by essential oil fractions from 2-5 min and 10-30 min, followed by oil fraction from 0-2 min. The strongest inhibition activity against Gram-negative Yersinia enterocolitica, and Gram-positive Clostridium perfringens, Enterococcus faecalis, and Staphylococcus aureus subs. aureus was observed with the control essential oil. This is the first study to describe significant activity of hops essential oils against Trypanosoma brucei, a parasitic protozoan that causes African trypanosomiasis (sleeping sickness in humans and nagana in other animals). Hops essential oil fractions or whole oil may be used as antimicrobial agents or for the development of new drugs.
... Diese Verbindungen werden von den Lupulindrüsen zusammen mit den Bitterstoffen sezerniert, wenn die Biosynthese der Bitterstoffe vollendet ist [65]. 1981 entwickelten Sharpe und Laws [98] eine Klassifikation, die alle bekannten Hopfenöle in drei Fraktionen unterteilt (Hydrocarbone, sauerstoffhaltige Verbindungen und schwefelhaltige Verbindungen) [70,98] [28]. Diese Gruppe der Prenylflavonoide stellt einen der wichtigen Vertreter der Polyphenole dar. ...
... Diese Verbindungen werden von den Lupulindrüsen zusammen mit den Bitterstoffen sezerniert, wenn die Biosynthese der Bitterstoffe vollendet ist [65]. 1981 entwickelten Sharpe und Laws [98] eine Klassifikation, die alle bekannten Hopfenöle in drei Fraktionen unterteilt (Hydrocarbone, sauerstoffhaltige Verbindungen und schwefelhaltige Verbindungen) [70,98] [28]. Diese Gruppe der Prenylflavonoide stellt einen der wichtigen Vertreter der Polyphenole dar. ...
... Alpha acids are the precursor of the main bittering compounds in beer, iso-alpha acids, and exist in hops, on average, 9 -10% by weight although this concentration is highly strain dependent (Steenackers et al. 2015). Sharpe and Laws (1981) classified hop oil components and found that 50-80% of the oil is comprised of hydrocarbons, while the rest includes sulfur-containing and oxygenated compounds (Sharpe and Laws 1981 Hops also impart preservative properties on a finished beer, improving flavor stability and acting as a mild antibacterial agent. Antioxidant compounds, like polyphenols, derived from hops are one of the main sources of flavor stability. ...
... Alpha acids are the precursor of the main bittering compounds in beer, iso-alpha acids, and exist in hops, on average, 9 -10% by weight although this concentration is highly strain dependent (Steenackers et al. 2015). Sharpe and Laws (1981) classified hop oil components and found that 50-80% of the oil is comprised of hydrocarbons, while the rest includes sulfur-containing and oxygenated compounds (Sharpe and Laws 1981 Hops also impart preservative properties on a finished beer, improving flavor stability and acting as a mild antibacterial agent. Antioxidant compounds, like polyphenols, derived from hops are one of the main sources of flavor stability. ...
Article
High gravity (HG) brewing has become the most used strategy for maximizing fermenter productivity in commercial brewing. While HG brewing has many benefits, the additional stress placed on the yeast due to the higher concentration of fermentable sugars in the wort can negatively impact fermentation performance and flavor compound formation. A proper dissolved oxygen (DO) level is vital to guarantee adequate yeast performance during HG fermentations. Dissolved oxygen is vital to yeast viability throughout the fermentation process, as yeast requires oxygen to synthesize vital cell membrane components needed for continued anaerobic growth and cell division. Previous research has demonstrated the importance of DO in wort for regular gravity fermentation and flavor compound production. However, the impact of dissolved oxygen during HG brewing on fermentation performance and how this will impact the production of flavor compounds have not been fully researched. The objectives of this research were to analyze the impact of wort aeration timing and concentration on fermentation performance, flavor stability, and the formation of volatile flavor compounds, determined using gas chromatography. Gas chromatography analysis was modeled after the ASBC Method Beer-48. Flavor stability and staling was analyzed during aging under normal and accelerated conditions utilizing TBA analysis. Pre-pitch oxygen treatments at levels greater than 8 ppm dissolved oxygen significantly increased attenuation when compared to the unoxygenated controls. Post-pitch oxygenation significantly increased attenuation, with DO treatments at levels of 8 ppm showed the most significant decrease in wort specific gravity. Aldehyde, ester, and higher alcohol production were all significantly affected by DO concentration. Aldehyde production decreased with increased DO concentration. Ester production increased from 0 to 8 ppm DO treatment and decreased at DO treatments greater than 8 ppm. Higher alcohol production increased from 0 to 10 ppm and decreased with DO treatments greater than 10 ppm. Greater concentrations v of DO resulted in greater TBA index values after normal and accelerated aging, with accelerated aging producing greater TBA index values than normal aging.
... Dry hops, commonly used in the brewing process, contain 0.5-2.0% of essential oils, which consist mainly of terpene hydrocarbons and their oxygenation products (Kovačevič and Kač 2002). More specifically, according to Sharpe and Laws (1981), all known hop oils 290 can be classified into three categories: hydrocarbons (containing monoterpenes, sesquiterpenes and aliphatic hydrocarbons), oxygenated compounds (terpene alcohols, sesquiterpene alcohols and other oxygenated compounds) and sulfur-containing compounds (thioesters, sulfides and other sulfur compounds). ...
... The quantitatively most abundant terpenoids in hops are the sesquiterpenoids, such as α-humulene (not to be confused with the hop α-acid humulone), β-caryophyllene and β-farnesene, and the monoterpenoid myrcene, which constitutes up to about 75% of hop essential oils (Sharpe and Laws 1981). Myrcene is an 300 important compound in the aroma of mango (Pino and Mesa 2006), and early studies in lemon and lime fruits have also indicated its importance for the aroma of these fruits (Moshonas and Shaw 1972;Njoroge et al. 1994). ...
Article
Full-text available
Aroma compounds provide attractiveness and variety to alcoholic beverages. We discuss the molecular biology of a major subset of beer aroma volatiles, fruity and floral compounds, originating from raw materials (malt and hops), or formed by yeast during fermentation. We introduce aroma perception, describe the most aroma-active, fruity and floral compounds in fruits and their presence and origin in beer. They are classified into categories based on their functional groups and biosynthesis pathways: 1) Higher alcohols and esters, 2) Polyfunctional thiols, 3) Lactones and furanones, and 4) Terpenoids. Yeast and hops are the main sources of fruity and flowery aroma compounds in beer. For yeast, the focus is on higher alcohols and esters, and particularly the complex regulation of the alcohol acetyl transferase ATF1 gene. We discuss the release of polyfunctional thiols and monoterpenoids from cysteine- and glutathione-S-conjugated compounds and glucosides, respectively, the primary biological functions of the yeast enzymes involved, their mode of action and mechanisms of regulation that control aroma compound production. Furthermore, we discuss biochemistry and genetics of terpenoid production and formation of non-volatile precursors in Humulus lupulus (hops). Insight in these pathways provides a toolbox for creating innovative products with a diversity of pleasant aromas.
... [31,46,47] For comprehensive compilations of hop terpenoids, refer to Eyres and Dufour, [22] Tressl et al., [31] Nance et al., [77] and Sharpe and Laws. [86] Terpenoids can either be products of biosynthesis or secondary reactions. Biosynthetic formation is tightly regulated at the genetic level (transcription); their synthesis involves multiple terpene synthases/cyclases. ...
... A comprehensive compilation of hop derived volatiles is given by Sharpe and Laws. [86] They listed approximately 60 aldehydes and ketones, 70 esters, 50 alcohols, 25 acids, and 30 oxygen containing heterocyclic compounds present in the hop oil. Indeed, the definite assignment of the origin of each specific compound is difficult. ...
Article
Hops are the most complex and costly raw material used in brewing. Their chemical composition depends on genetically controlled factors that essentially distinguish hop varieties and is influenced by environmental factors and post-harvest processing. The volatile fingerprint of hopped beer relates to the quantity and quality of the hop dosage and timing of hop addition, as well as the overall brewing technology applied. Analytically, the aroma of hops and the flavor of hoppy beers cannot be measured by quantification of a single odorant; moreover, the selection of several key compounds or a comprehensive characterization (profiling) seems reasonable. Analysis of hops and beer is challenging. The selective enrichment of volatiles from complex matrices, separation, unambiguous identification, and precise quantification are the keywords used in this context. This review outlines the synthesis of relevant hop aroma compounds within the plant. The process that incorporates hops into the final beer is described using the hopping techniques used in the industry. Due to the complexity and multiplicity of chemical compounds found in hops, an attempt was made to simplify the information presented by separating the chemical compounds considered into two broad groups: terpenoids and nonterpenoids. This review summarizes approaches commonly used for analysis of hop aroma compounds in hops and beer.
... However, understanding kettle hop flavor is still complicated, and the chemistry of kettle hop flavor has yet to be fully elucidated. Significant research efforts fail to confirm that hop essential oils are unequivocally responsible for production of the kettle hop flavor in beer (39,78,94,(181)(182)(183)199). In the brewing process hops are usually added to wort, which is, of course, largely an aqueous solution. ...
... To date, over 300 constituents in hop essential oils have been identified. Sharpe and Laws (199) indicated that hop oil consists of three classes of compounds: hydrocarbons, oxygenated compounds, and sulfur-containing compounds. About 70% of the hydrocarbons are represented by a group of terpenes and sesquiterpenes including myrcene, humulene, and caryophyllene. ...
Article
Over the last century, the brewer's archetype of hop chemistry, hopping technology, hop utilization, and hop flavor has substantially transformed. During the 1950s Miller Brewing Company began pioneering work to unravel some of the mysteries of hop chemistry. This work, combined with research findings from various other groups throughout the world, revolutionized the industry. Such realizations of hop chemistry and hop technology in addition to the widening array and understanding of aromatic hop varieties allow the modern practical brewer a diverse palette of hopping choices to ensure production of highly consistent, flavorful, quality beers. Today, brewers may artfully and innovatively craft beers with enhanced properties such as light stability, increased foamability/head retention, enriched hop flavors, optimized beer mouthfeel, increased hop utilization, and improved microbial and flavor stability. This paper guides the reader through a history of hop chemistry, revealing the "bitter, twisted truth of the hop" from the discovery of hop acids and their transformations to the many innovations that led to the development of advanced hops and novel hop products necessary for the successful development of new and novel beer brands of consistent quality in a large brewery scenario. This paper also provides a framework from which the smaller, craft brewer can take advantage of the more recent developments in hop chemistry to gain enhanced quality, consistency, economy, and novelty moving forward.
... The Table 1 presents classification of hop oil. Source: Own work based on [6] The component with the highest content in essential oils (20 -70%) is volatile and very susceptible to oxidation is the monoterpene myrcene. Threshold of perceptibility for myrcene in the beer is about 120 µg/l. ...
... Takoi et al. showed that geraniol is metabolized by yeast into β-citronellol rapidly during the primary fermentation in 2-4 days after beginning [8]. Other work showed the bioconversion with yeasts of geraniol to β-citronellol is also accompanied by the by stream synthesis of geranyl acetate and citronellyl acetate [6]. King and Dickinson elaborated the scheme of biotransformation of geraniol and nerol by S. cerevisiae for 4 possible outcomes: citronellol, linalool, αterpineol, and terpin hydrate [7]. ...
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Due to the significant changes on the beer market the flourishing development of small and craft breweries is clearly observed. Upgraded consumers’ expectation led to many technological challenges in brewing process resulting in novel methods of manufacturing of many different beer types. As bitterness and aroma are two crucial quality features of beer and many scientific efforts have been done especially in the area of hop aroma. Despite the predominant impact of main beer flavor compound e.g. linalool, other substances also contribute to the hoppy beer aroma through additive or synergistic effects not only raw materials used but also hopping regimes contribute as well to final flavor release though several new methods of hopping, particularly dry hopping have been developed.
... Over time over 1000 different compounds in the hop oil fraction were identified [19]. Currently, three main chemical groups of oils are recognized, in which hydrocarbons and oxygenated compounds predom-inate and sulfur-containing components are represented to lesser extent [53]. Structures of the main members of the hop oils group are shown inFigure 5. Several studies determined the correlation of hydrocarbon fraction patterns with hop variety and growing locality54555657. ...
... Structures of the main members of the hop oils group are shown inFigure 5. Several studies determined the correlation of hydrocarbon fraction patterns with hop variety and growing locality54555657. Hydrocarbons are classified as aliphatic hydrocarbons (pentane, octane, isoprene, undecane, dodecane, etc.), monoterpenes (β-myrcene, limonene, p-cymene, α-pinene, β-pinene) and sesquiterpenes (α-farnasene, β-farnesene, α-humulene, β-caryophyllene , etc.) [53, 58]. These compounds are very volatile and they easily undergo oxidation and polymerization. ...
Article
Hops are a well-known source of resins, essential oils and polyphenolic substances, such as proanthocyanidins or prenylflavonoids with significant representatives of xanthohumol, isoxanthohumol, and 8-prenylnaringenine, and represent an essential ingredient in beer production. Recently, however, many additional bioactive effects of hop compounds have been investigated. A systematic review of the structure-function relationship between the individual hop-derived compounds and their bio-activity has been lacking. In this review we summarize some recent findings in this area from reports from our as well as other studies. It shows multiple bio-medical effects of the individual hop derived compounds, which can act individually, or in a synergistic manner. The hops can serve as a source of bio-active compounds in phyto-medicine and as such, more attention and detailed studies are warranted to utilize the broad spectrum of effects of individual compounds in future treatments.
... These compounds are secreted from the lupulin glands, along with bitter acids, when the biosynthesis of bitter acids is complete (Briggs and others 2004). In 1981, Sharpe and Laws (1981) introduced a classification system where all known hop oils were divided into 3 fractions: hydrocarbons (contain monoterpenes, sesquiterpenes, and aliphatic hydrocarbons), oxygenated compounds (terpene alcohols, sesquiterpene alcohols, and other oxygenated compounds), and sulfur-containing compounds (thioesters, sulfides, and other sulfur compounds). The most abundant representatives of the hydrocarbon fraction (50% to 80% of total oil) are the monoterpenes αand β-pinene, myrcene, and limonene ( Figure 3A), and the sesquiterpenes αhumulene, β-farnesene, β-caryophyllene, αand β-selinene, and γ -muurolene ( Figure 3B). ...
... hop ripening, processing, and storage (Howard and Slater 1957). It is a complex mixture of terpenic alcohols, aldehydes, ketones, epoxides, acids, and esters (Sharpe and Laws 1981). The most extensively studied compounds from the oxygenated fraction are linalool, geraniol, caryophyllene oxide, and farnesol ( Figure 3C). ...
Article
Although female cones of the hop plant (Humulus lupulus) are known primarily as raw material supplying characteristic bitterness and aroma to beer, their equally significant health-promoting effects have been known to mankind for several thousand years and hop is a plant traditionally utilized in folk medicine. This paper summarizes the scientific knowledge on the effects of all 3 major groups of secondary metabolites of hops; polyphenols, essential oils, and resins. Because of their chemical diversity, it is no coincidence that these compounds exhibit a wide range of pharmacologically important properties. In addition to antioxidant, anti-inflammatory, and anticancer-related properties, particular attention is being paid to prenylflavonoids that occur almost exclusively in hops and are considered to be some of the most active phytoestrogens known. Hop oils and resins are well known for their sedative and other neuropharmacological properties, but in addition, these compounds exhibit antibacterial and antifungal effects. Recently, alpha bitter acids have been shown to block the development of a number of complex lifestyle diseases that are referred to by the collective name "metabolic syndrome." Information presented in this review confirms the significant potential for the use of hops in the pharmaceutical industry and provides an understanding of beer as a natural drink that, although moderately consumed, may become a source of many health-promoting compounds.
... However, understanding kettle hop flavor is still complicated, and the chemistry of kettle hop flavor has yet to be fully elucidated. Significant research efforts fail to confirm that hop essential oils are unequivocally responsible for production of the kettle hop flavor in beer (39,78,94,(181)(182)(183)199). In the brewing process hops are usually added to wort, which is, of course, largely an aqueous solution. ...
... To date, over 300 constituents in hop essential oils have been identified. Sharpe and Laws (199) indicated that hop oil consists of three classes of compounds: hydrocarbons, oxygenated compounds, and sulfur-containing compounds. About 70% of the hydrocarbons are represented by a group of terpenes and sesquiterpenes including myrcene, humulene, and caryophyllene. ...
... However, more recent studies have suggested that it could be closer to 1000. Sharpe and Laws (Sharpe & Laws, 1981) separated constituents of this fraction into 3 groups: hydrocarbons, oxygen-containing compounds, and sulfur compounds. Chemically, 50-80% of the hop essential oil compounds are hydrocarbons, which can be divided into monoterpenes, sesquiterpenes and aliphatic compounds. ...
Article
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Besides providing bitterness to beer, hops also impart a whole range of aromas, such as herbal, spice, floral, citrus, fruity and pine to this beverage. Although hops are usually added in relatively small amounts, they have a significant impact on the sensory characteristics of the product. Raw hop aroma significantly differs from the aroma resulting from its addition to the beer. The final aroma of the beer arises from substances in the malt, hops, other additives, and yeast metabolism. The biochemical transformation of hop compounds by yeast has become more and more popular in recent years. Knowledge of this process may allow more precise control over the final sensory characteristics of the beverage. The article describes the chemical composition of hops and discusses the influence of the hopping regime on the concentration of volatile compounds in the finished product. Moreover, the article describes the biotransformation of hop-derived compounds by traditionally used Saccharomyces cerevisiae yeast, as well as less commonly used non- Saccharomyces yeast. The paper outlines the current state of knowledge on biotransformation of hop-derived hydrocarbons, terpenoids, esters, sulfur compounds and glycosidically bound aroma precursors.
... The synthesis and the complex profile of hop essential oils is highly genotype-dependent and strongly influenced by environmental and cultural conditions [14]; the hop aromatic profile is constituted mainly by three chemical groups: hydrocarbons (50-80%), oxygenated compounds (20-50%) and organosulfur compounds (<1%) [15]. Among hydrocarbons, the most representative fraction is represented by terpenes that, being highly volatile, tend to vanish during the brewing process [16][17][18]. ...
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Background: Northern Italy has an enormous heritage of hop biodiversity that need to be exploited and studied. The preservation and valorization through the characterization of the existent biodiversity is a primary goal of the European Green Deal 2023–2030. The aim of this study was to acquire information on the biodiversity of Italian wild hops. Methods: Genetic characterization of sixty accessions was done resorting to Single Sequence Repeated (SSR) markers. Phytochemical characterization of wild hops was achieved using: (i) high-performance liquid chromatography with ultraviolet detection for bitter acids quantification, (ii) steam distillation for essential oils quantification and (iii) Gas Chromatography-Mass Spectrometry for the determination of the aromatic profile. Results: The eight SSR primers showed high Polymorphic Information Content (PIC), especially HlGA23. α-Acids reached values between 0 and 4.125. The essential oils analysis highlighted variability within the studied population, with some accessions characterized by important spicy fraction, and others by fruity and floral notes. Conclusions: The present study allowed the characterization of Italian wild hops and demonstrated an interesting biodiversity. Part of this biodiversity have been shown to be potentially suitable for use in brewing. Moreover, several genotypes could be used in breeding programs to obtain new more sustainable varieties.
... The range of total hops oil lost during hopsdrying have been reported to be between 10% and 60%. [10] According to Sharpe & Laws, [33] the highest drying temperature at which the loss of essential oil can be kept at a reasonable margin (around 3%) is 63 C. According to He rm anek et al., [34] the chemical composition of hops on average includes 15% of total resins, 4% of polyphenol-type substances (also known as hop tannins) and 1% essential oil, all of which are deemed crucial as brewing constituents. Desmethylxanthohumol is one of the important polyphenol-type substances that contribute to a pronounced and crispy beer taste alongside exhibiting a precipitating effect on proteins with high and intermediate molecular weight during hopping. ...
Article
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Hops are an essential raw material in beer brewing, providing typical flavor and aroma characteristics to beer. Freshly harvested hop cones must be dried immediately. While conveyor-belt dryers are widely used, their operation is largely based on operator experience, which leads to energy-intensive operation whilst adversely affecting the quality. This work identifies the bottlenecks in hops drying by summarizing the results of previous studies, and experimentally analyzing an industrial dryer. Heterogeneous air-distribution, uneven drying and suboptimal control-strategies were identified as key issues which can be battled with accurate model-based process analysis and smart control systems, both of which need further research.
... Like bitter components, aromatic components are located in the lupilin glands. Essential oils make up 0.5-3% of the dried hop weight (Sharpe and Laws, 1986;Steinhaus and Schieberle, 2000). In contrast to the bitter components, which are mainly affected by degradation due to high water activity levels over an extended period of time, aromatic compounds and essential oils are highly volatile and susceptible to degradation before, during and after the drying process (Aberl, 2016). ...
Article
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Hops are a key ingredient for beer brewing due to their role in preservation, the creation of foam characteristics, the bitterness and aroma of the beers. Drying significantly impacts on the composition of hops which directly affects the brewing quality of beers. Therefore, it is pivotal to understand the changes during the drying process to optimize the process with the central aim of improving product quality and process performance. Hops of the variety Mandarina Bavaria were dried at 65°C and 70°C with an air velocity of 0.35 m/s. Bulk weights investigated were 12, 20 and 40 kg/m 2 respectively. Drying times were 105, 135, and 195 and 215 min, respectively. Drying characteristics showed a unique development, very likely due to the distinct physiology of hop cones (spindle, bracteole, bract, lupilin glands). Color changes depended strongly on the bulk weight and resulting bulk thickness (ΔE 9.5 (12 kg), 13 (20 kg), 18 (40 kg)) whilst α and ß acid contents were not affected by the drying conditions (full retention in all cases). The research demonstrated that specific air mass flow is critical for the quality of the final product, as well as the processing time required. Three types of visual sensors were integrated into the system, namely Vis-VNIR hyperspectral and RGB camera, as well as a pyrometer, to facilitate continuous in-process measurement. This enabled the dynamic characterization of the drying behavior of hops. Chemometric investigations into the prediction of moisture and chromatic information, as well as selected chemical components with full and a reduced wavelength set, were conducted. Moisture content prediction was shown to be feasible (r 2 = 0.94, RMSE = 0.2) for the test set using 8 wavelengths. CIELAB a* prediction was also seen to be feasible (r 2 = 0.75, RMSE = 3.75), alongside CIELAB b* prediction (r 2 = 0.52 and RMSE = 2.66). Future work will involve possible ways to improve the current predictive models.
... Hop cultivars can confer distinct flavour and aroma characteristics to beer, which are attributable to the accumulated phytochemistry of hop cones (Almaguer et al., 2014). A complex pool of volatile secondary metabolites comprised of hydrocarbons (monoterpenes, sesquiterpenes, and aliphatics), oxygenated compounds (alcohols, epoxides, esters, and ketones), and sulfur-containing compounds, accumulate in hop cones, which contributes to the unique organoleptic properties of particular cultivars noted in beer (Sharpe & Laws, 1981;Steenackers, De Cooman, & De Vos, 2015). Characteristic essential oil profiles extracted from hop cones have been used to identify cultivars, determine genetic variability or diversity, and interpret aroma properties (Kovačevič & Kač, 2002;Patzak, Nesvadba, Henychová, & Krofta, 2010). ...
Article
This study investigated the volatile phytochemical diversity of 30 samples obtained from experimental hybrid and commercial H. lupulus L. plants. Essential oils distilled from these samples were analysed by high resolution gas chromatography coupled with accurate mass time-of-flight mass spectrometry (GC–accTOFMS). A total of 58 secondary metabolites, mainly comprising 18 esters, 6 monoterpene hydrocarbons, 2 oxygenated monoterpenes, 20 sesquiterpene hydrocarbons, 7 oxygenated sesquiterpenes, and 4 ketones, were positively or tentatively identified. A total of 24 metabolites were detected in all samples, but commercial cultivars (selected for brewing performance) had fewer compounds identified compared to experimental genotypes. Chemometrics analyses enabled distinct differentiation of experimental hybrids from commercial cultivars, discussed in terms of the different classes of compounds present in different genotypes. Differences among the mono- and sesquiterpenoids, appear to be related to either: i) the genetic origin of the plants; or ii) the processes of bioaccumulation of the identified secondary metabolites.
... Though preliminary work (data not shown) resulted in the tentative identification of 4-mercapto-4-methylpentan-2-one (4MMP) via RI match of aroma event, it was not positively identified in this study. Dating back to the early reviews on hop oil, [40] as well as more recent work, [1] the role of polyfunctional thiols in hops and their contribution to beer flavor has been well-stated [41,42] and should still be considered as potential drivers of dry-hop aroma. ...
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Cascade, Chinook, and Centennial hops are used extensively throughout the brewing industry either individually or in various combinations to add hoppy aroma to beer. This high use of hops, particularly via late- or dry-hopping, creates a need to better understand the chemical contribution of these hop varieties during dry-hopping beer in order to predict brewing performance. Solvent-Assisted Flavor Evaporation (SAFE) and Aroma Extract Dilution Analysis (AEDA) was performed on unhopped beer that was dry-hopped individually with each of these varieties as well as the unhopped base. This technique was used to determine the aroma compounds that were the greatest contributors to the dry-hop character of these hops. The analysis of beer prepared with Cascade, Chinook, and Centennial identified 9, 10, and 11 character impact compounds, respectively. Commonalities were observed among the three varieties regarding 2-furanmethanol, linalool, geraniol, cis-geranic acid methyl ester, and n-decanoic acid in dry-hopped beer. Variation between the hop volatiles found to be important for Centennial and Chinook dry-hop aroma was a function of only a few character impact compounds, whereas Cascade was slightly different, anchored heavily by benzenacetaldeyde. The relative similarities and differences that these three hop cultivars attribute to beer during dry-hopping were revealed by comparing which compounds were important for the characteristic aroma profiles of these cultivars in single dry-hop beers.. This knowledge is important for brewers wishing to introduce potential replacement hops and/or reductions for these hop cultivars in the future and guide the direction of future blending studies.
... Myrcene is a monoterpene polyunsaturated acyclic found in nature, which is more abundant in essential oil of several plants including Spilanthes acmella, Cannabis sativa, Humulus lupulus, Houttuynia emeiensis and Houttuynia cordata (Sharpe & Laws 1981;Baruah & Leclercq 1993;Mediavilla & Steinemann 1997;Lu et al. 2006). Studies on mammals show myrcene analgesic effects are mediated by stimulation of the arginine-NO-cGMP and increase in cGMP [see Guimarães et al. (2013)]. ...
Article
Anaesthesia is a widely used tool in fish handling, sampling and surgery in aquaculture; thus, fish anaesthesiology has been studied for a long time. In this case, there are several common anaesthetics in aquaculture, namely tricaine methanesulfonate (a chemical agent) and clove oil (a natural agent). Recently, there was an increasing interest to use herbal materials (other than clove oil) in fish anaesthesia. In this review, current knowledge about the use of herbal anaesthetics has been summarized. To date, essential oils/extracts of different plants have been studied for fish anaesthesia; most of them belong to Lamiaceae, Verbenaceae, Lauraceae and Myrtaceae. In addition, menthol, linalool, myrcene, cineole, globulol, spathulenol, guaiol, caryophyllene oxide, terpinen-4-ol and dehydrofukinone are herbal compounds that their anaesthetic effects have been studied in fish. Compared with clove oil and eugenol as the most common herbal anaesthetic, all tested herbal materials are less efficacious to anaesthetize fish. Some plants’ essential oil/extract, namely Aloysia triphylla, Myrcia sylvatica, Lippia alba and Curcuma longa, have beneficial health effects including suppression of physiological and oxidative stress. There is a lack of data in mechanism of anaesthesia and health effects of the herbal anaesthetics, which should be followed in future studies. In addition, most of the current studies have focused on certain fish species such as silver catfish (Rhamdia quelen), tambaqui (Colossoma macropomum) and common carp (Cyprinus carpio), and in most of the studies, essential oils/extracts of South American plants have been used. Thus, there is a need to study other fish and plant species.
... For instance, E,E-? and E-?-farnesene are attractive to both female mice ( Jemiolo et al. 1991) and female Norway rats ( Ponmanickam et al. 2010). Farnesenes are also found in hops (Sharpe & Laws 1981), possibly explaining the folk knowledge that beer is a good attractant for mice. However, high concentrations of farnesenes may be needed to attract female mice if used on their own ( Jemiolo et al. 1991). ...
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To improve conservation outcomes and move towards a ‘predator-free New Zealand’, we need new pest control technologies. Our growing knowledge of the chemistry, behaviour and neuroendocrinology of mammalian scents that affect other individuals (semiochemicals) provides an opportunity for these to be used in various ways to help to control pest species. In this report, we summarise current knowledge of attractant semiochemicals (pheromones) of rodents, mustelids, cats and possums in New Zealand, to find potential avenues for the development of lures and other control strategies. Putative pheromones have been identified in all these species, and the major urinary proteins (MUPs) and peptides derived from the major histocompatibility complex (MHC) have been shown to play a role as pheromone carriers in the house mouse (Mus musculus), Norway rat (Rattus norvegicus) and ship rat (R. rattus). In addition, attractant compounds have been identified in the urine and glands of cats (Felis catus), mustelids (stoats – Mustela erminea, weasels – M. nivalis and ferrets – M. furo) and brushtail possums (Trichosurus vulpecula), and the calming effect of the feline facial pheromone has been explored. There are several potential applications for pheromones in mammalian pest management, including in trap and lure-and-kill systems; toxic baits; immunocontraception or chemosterilisation delivery systems; monitoring for incursions; interruption of breeding behaviour; and enhancement of biological control. The learned component of responses to pheromones and the role of MUPs in that learning suggest a complex system and it is unlikely that there will be a single ‘magic bullet’ solution for all pest species, but some potential for inter-species attractants. The use of novel control strategies based on a sound understanding of animal behaviour and neurophysiology could see pheromones and MUPs being combined to help improve predator control in New Zealand.
... Depending on the extraction conditions, CO 2 extracts contain mostly the nonpolar compounds found in hops, including the essential oil fraction, whereas ethanol extracts typically include more of the polar components, such as some polyphenols (xanthohumol, for instance) and chlorophyll. The chemical profile of the essential oil fraction varies by cultivar (16) but consists primarily of volatile hydrocarbons, oxygenated components, and sulfur-containing components (20). For the most part, these compounds are relatively volatile and minimally soluble in an aqueous matrix such as wort. ...
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Brewers who create hop-forward styles such as American-style India Pale Ales typically add hops toward the end of or after wort boiling to avoid aroma volatilization and thereby impart strong hop-derived aromas. However, previous studies have demonstrated that despite the volatilization effects of boiling wort, hops that are added early in kettle boil can contribute to hop aroma. Nonvolatile hop-derived precursors, specifically glycosides, may survive the boiling process and become hydrolyzed to release volatile aglycones capable of contributing to aroma. Twelve single-hopped pilot-scale (3 hL) beers were brewed using pellet, supercritical CO 2 extract, and spent hop fractions of Citra, Simcoe, Centennial, or Cascade cultivars to investigate the contribution of these different hop fractions to the aroma of kettle-hopped beers. Pellet, extract, and spent additions consisted of a single hop addition 5 min into a 60 min boil. Volatile analysis of beers was performed using stir-bar sorptive extraction and quantified using gas chromatography–mass spectrometry. Beers were analyzed for the common terpenoid compounds -pinene, -pinene, -myrcene, limonene, linalool, E,-caryophyllene, -humulene, and -terpineol. In addition, beers were evaluated using descriptive sensory analysis. The descriptive sensory data identified significant differences among the cultivar and hop product treatments. The spent hop treatments produced beers that had a noticeable hop aroma, which suggests that the water-soluble components left behind in the spent hops may contribute to hop aroma in beer. The intensity and nature of the hop aroma in the spent treatments were hop variety specific. However, the contributions of water-soluble components found in spent hops to increased aroma intensity in beer were small, especially compared with the pellet and extract treatments.
... The essential oils are an important class of hop compounds, giving the hops their specific aroma. As each hop variety has a typical essential oil pattern, the analysis of hops' essential oils can be used to identify hop varieties (Sharpe & Laws, 1981). The essential oil pattern of hop varieties was used as input data for chemometric analysis in this study. ...
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This study describes the analysis of total hops essential oils from 18 cultivated varieties of hops, five of which were bred in Lithuania, and 7 wild hop forms using gas chromatography-mass spectrometry. The study sought to organise the samples of hops into clusters, according to 72 semi-volatile compounds, by applying a well-known method
Article
In Saccharomyces, the IRC7 gene encodes for a cysteine S-conjugate β-lyase enzyme which can release polyfunctional thiols from their cysteinylated precursor forms, thereby promoting thiol aroma in beer. This study examined the thiol production of 10 commercial yeast strains in two different media, a hopped yeast extract-peptone-dextrose (YPD) medium and a 100% barley malt wort to explore how differences in yeast strain and medium conditions influence the release of polyfunctional thiols. 3-Sulfanylhexan-1-ol was most affected by medium conditions, and its concentrations were highest in wort fermentations. The higher nitrogen content and pH of the YPD medium relative to the wort fermentations were notable differences, and significant correlations between these variables and the extent of free thiol production were observed. A strong association existed between polyfunctional thiol concentrations and the fermentation-derived, malt, and hop-derived compounds 2-phenylethanol, β-damascenone, and β-ionone. The sensory impressions of thiol character in beer were influenced by the presence of other aromatic compounds such as esters and terpene alcohols, and aroma attributes such as "tropical" were not the most suitable for describing beers brewed with yeasts that fully express homozygous IRC7F. Sensory attributes "sweaty", "vegetal", and "overripe fruit" were more strongly associated with these strains.
Article
Supercritical fluid extraction from hops (Humulus lupulus L.) can be used to extract essential oil for the flavoring of beer. With a special focus on the oil composition being linked to the hop aroma, the influence of pressure and temperature on the extraction kinetics of seven oil components (β-myrcene, α-humulene, β-caryophyllene, 2-methylbutyl isobutyrate, undecanone, linalool, and α-pinene) is analyzed and modeled in this article. Supercritical CO2 extraction from hop pellets was conducted at pressure-temperature combinations of 90/100/110 bar and 40/45/50 °C. The extract composition over time, analyzed by gas chromatography, was used for the parameterization of two existing mechanistic models: an internal-mass-transfer-control (IMTC), and a broken-and-intact-cells (BIC) model. The IMTC model was found to effectively describe most extraction kinetics and hence applied in this study. In contrast to previous studies, the IMTC model parameters were not only fitted to individual extraction curves from different experiments but also correlated to temperature and pressure as a further step towards model-based prediction. Using the parameterized model, the extract composition was predicted at 95 bar/48 °C, 105 bar/42 °C, and 105 bar/48 °C. Extraction yields were found to be higher at lower temperatures and higher pressures in general. The sensitivity towards pressure was observed to differ between components and to be particularly higher for β-myrcene compared with α-humulene. Changes of the essential oil composition with a variation in pressure and temperature were predicted correctly by the model with a mean relative deviation from experimental data of 11.7% (min. 1.2%, max. 36.2%).
Article
Model systems of adding three distillates (hop oil, water-soluble aqueous, and residual aqueous) in model wort (buffer) and wort were used to produce model beers and special beers, respectively (with an ale yeast and fermentation at 18 °C). The attributes of hoppy flavor and organoleptic quality were comprised of sustained, surged, generated, or diminished oxygenated compounds and hydrocarbons by yeast biosynthesis in hop essential oil and non-volatile precursors. The matrix of content and instrumental composition of oxygenated terpenoids and hydrocarbons (terpenes and sesquiterpenes) and sensorial profile of model systems was directionally correlated to the matrix and sensory of the early hopped, late hopped, and dry hopped beers. The occurrence of hop aroma profile of the residual aqueous is reminiscent to traditional early kettle hopped beer. The water-soluble volatile components added beer were remarkably close to the distinctive odor profile of late hopped beer. However, dry hopped beer was seemingly a coupling of the hop oil and the water soluble aqueous added beers, but its perception was closer to the latter. The mechanism of the growth of nerol, citronellol, and methyl geranate via a reversed biosynthesis of free linalool by ale yeast and fermentation at 18 °C is contrary to a pathway via geraniol from the hop oil or the water-soluble aqueous. Free linalool was sustained after yeast hydrolysis of linalyl glycoside and related to metabolites in the residual aqueous due to sluggish yeast activity in the model wort (buffer) but not in the wort.
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The biotransformation of hop aroma, particularly by the cysteine S-conjugate beta-lyase enzyme (CSL), has been a recent topic of tremendous interest among brewing scientists and within the brewing community. During a process often referred to as biotransformation, yeast-encoded enzymes convert flavorless precursor molecules found in barley and hops into volatile thiols that impart a variety of desirable flavors and aromas in beer. Two volatile thiols of particular interest are 3-mercaptohexan-1-ol (3MH) and its acetate ester, 3-mercaptohexyl acetate (3MHA), which impart guava and passionfruit flavors, respectively. In this study, a parental Saccharomyces cerevisiae brewing strain that displayed low thiol biotransformation activity was genetically manipulated (GM) to substantially increase its thiol biotransformation potential. Construction of this GM strain involved integration of a gene encoding a highly active CSL enzyme that converts thiol precursors into the volatile thiol, 3MH. Three additional strains were subsequently developed, each of which paired CSL expression with expression of an alcohol acyltransferase (AAT) gene. It was hypothesized that expression of an AAT in conjunction with CSL would increase production of 3MHA. Fermentation performance, sensory characteristics, and 3MH/3MHA production were evaluated for these four GM strains and their non-GM parent in 1.5hL fermentations using 100% barley malt wort hopped at low levels with Cascade hops. No significant deviations in fermentation performance (time to attenuation, final gravity, alcohol content, wort fermentability) or finished beer chemistry were observed between the GM strains and the parent strain with the exception of the speed of vicinal diketones reduction post-fermentation, which was quicker for the GM strains. The GM strains produced beer that had up to 73-fold and 8-fold higher 3MH and 3MHA concentrations than the parent strain, achieving concentrations that were up to 79-fold greater than their sensory detection thresholds. The beers were described as intensely tropical and fruity, and were associated with guava, passionfruit, mango, pineapple and sweaty aromas. These experiments demonstrate the potential of genetic modification to dramatically enhance yeast biotransformation ability without creating off flavors or affecting fermentation performance.
Article
Terpenes are one of the main classes of compounds in hops (Humulus lupulus, L). They play an important role in brewing due to their central function, which is related to beer aroma. A screening of terpenes in several commercial hop varieties was carried out by gas chromatography coupled to mass spectrometry after employing a simple, straightforward and high throughput extraction method. A single batch extraction, using hexane as solvent, was employed to obtain the terpenic fraction of the hop samples. Nineteen terpenes were identified in analyzed samples with β-myrcene (2.22–45.30%), α-humulene (20.20–67.64%), and β-caryophyllene (9.97–24.62%) being the major terpenes in all samples. The studied system was multivariate modeled by principal component analysis. Based on the proposed approach, it was possible to correlate the terpenic hop profiles to their specific purpose in the brewing industry and to distinguish aromatic hops (high α-humulene content), bittering hops (high β-myrcene content), and dual-purpose hops (more complex and intermediate terpenic profile) among the samples.
Article
The first harvest of Humulus lupulus (var. Cascade) in Brazil in 2016 originated as an aromatic hop that nowadays is gaining attention from the brewery industry. However, the chemical composition and the properties of this hop have not been well documented to date. In this study, the chemical profile of the phenolic compounds and essential oils of Cascade hops produced in Brazil (BH) and the USA (UH) was determined. The major phenolic compounds identified by LC-ESI-MS-MS in BH and UH were protocatechuic acid, isoquercitrin, and ferulic acid (4.18–11.39; 2.44–4.90; and 1.45–4.48 mg 100 g−1, respectively). The profile of essential oils was shown to differ between the two samples. The compounds trans-β-farnesene (20.60%), β-selinene (18.78%), myrcene (16.57%), and α-selinene (16.22%) were the main compounds in the BH essential oil, while the essential oil of UH showed a high content of α-humulene (35.35%), myrcene (22.35%), β-caryophyllene (12.81%), and trans-β-farnesene (10.59%). A higher antioxidant activity (by DPPH and ABTS) was observed for hop extracts when compared to the essential oils. The results indicated that the Brazilian hop sample analyzed had higher radical scavenging when compared to an American hop sample (associated with its bioactive compound composition). The Cascade hop from Brazil appears to be a high-quality raw material showing significant potential for future industrial applications.
Article
Full-text available
Hops (Humulus lupulus L.) are used traditionally in the brewing industry to confer bitterness, aroma, and flavor to beer. However, in recent years, it has been reported that female inflorescences contain a huge variety of bioactive compounds. Due to the growing interest of the consumers by natural ingredients, intense research has been carried out in the last years to find new sources of functional molecules. This review collects the works about the bioactive potential of hops with applications in the food, pharmaceutical, or cosmetic industries. Moreover, an overview of the main extraction technologies to recover biomolecules from hops is shown. Bioactivities of hop extracts such as antibacterial, antifungal, cardioprotective, antioxidant, anti-inflammatory, anticarcinogenic, and antiviral are also summarized. It can be concluded that hops present a high potential of bioactive ingredients with high quality that can be used as preservative agents in fresh foods, extending their shelf life, and they can be incorporated in cosmetic formulation for skincare as well.
Article
Dysphania is an abundant genus of plants, many of which are endemic to the Australian continent, occurring primarily in arid and temperate zones. Despite their prevalence, very few investigations into the phytochemistry of native Dysphania have been undertaken. Described herein, is the isolation and elucidation of two enantiomeric diastereomers of humulene diepoxide C from D. kalpari and D. rhadinostachya, of which unassigned diastereomers of humulene diepoxide C have been previously reported as components in beer brewed from aged hops. In addition, two (+)‐humulene diepoxiols (humulene diepoxiol C‐I and C‐II) were isolated from D. rhadinostachya. Analysis of Chinook hops oil confirmed the presence of both humulene diepoxide C‐I and C‐II as trace components, and in turn enabled GC‐MS peak assignment to the relative stereochemistry. Anticancer assays did not reveal any significant activity for the (+)‐humulene diepoxides. Antifungal assays showed good activity against a drug‐resistant strain of C. auris, with MIC50 values of 8.53 and 4.91 μm obtained for (+)‐humulene diepoxide C‐I and C‐II, respectively. Eliciting from desert: The Australian desert plants Dysphania kalpari and D. rhadinostachya have yielded the first example of naturally occurring humuluene diepoxide C‐I and C‐II, which facilitated the assignment of the relative stereochemistry to these diepoxides that have origins in aged hops. Two new humulene diepoxiols were also isolated. The two diepoxides were observed to display good antifungal activity against a drug‐resistant C. auris strain.
Article
Fatty acids (FA) are minor compounds in beer and its raw materials, but can develop important roles in brewing and require monitoring. The aim of this work was to show the potential of capillary electrophoresis for fast hop analysis and to propose a simple method for the determination of saturated and unsaturated FA in different hop varieties. Sample preparation was investigated and evaluated and validation procedures were carried out to determine palmitic, stearic, oleic and linolenic FA in hops. Low values of relative standard deviation for areas (< 5.32%) and good recoveries (85-110%) were achieved. Laborious extraction and derivatization reactions were not necessary and only a saponification reaction was employed in sample preparation. Also, specific columns were not required and analysis time was only 10 min. The proposed methodology appears promising for faster monitoring of FA in terms of hop quality control in the brewing industry.
Article
Karahana ether and hop ether were detected in 12 selected hop oils and eight commercial hop extracts, but not in any of the three pilot beers or two commercial American beers analyzed. The best estimated thresholds of hop ether and karahana ether in beer are 506 and 98 μg/L, respectively. Both compounds show a strong floral but weak hoppy note in sensory analysis. It was concluded that neither hop ether nor karahana ether can be a major beer flavor constituent, especially in American beer.
Chapter
Alcoholic beverages are produced by fermentation of sugars to ethanol. Starting materials range from simple sugars to complex carbohydrates that are reduced to simple sugars by hydrolytic cleavage of starches and dextrins. Beer and wind represent direct products from fermentation whereas vodka, rum, whiskey and other distilled spirits and a distillation step.
Article
SA-1 hops are fine aroma hops that have played important roles in the brewing industry in China and abroad. The objective of this study was to use headspace solid-phase microextraction gas chromatography- mass spectrometry combined with chemometrics to determine the mechanism by which the flavor and composition of volatile components in SA-1 hops change in a freshness-dependent manner. Thirty common volatile components were identified, most of which contributed significantly to hops aroma. The results showed that the chemical composition of the stored and fresh SA-1 hops varied; there was a decrease in the amount of terpenes and an increase in oxygenated compounds in stored hops, indicating that significant changes had occurred during storage. Analysis of variance showed that the two batches of SA-1 hops differed significantly; cluster analysis also showed that the two batches of SA-1 hops were divided into two groups. Principal component analysis generated a simple classification and reflected the changes in composition of the SA-1 hops of different freshness by certain principal indices. Seven components represented the principal indices of the fresh hops, whereas nine components represented those of the stored hops. The odor of the fresh hops was fruity, whereas the odor of the stored hops was herbal and woody.
Conference Paper
Upscaling of dry-hopping trials M. Schnaitter1, A. Kell2, H. Kollmannsberger1, F. Schuell3, M. Gastl1 and T. Becker1 1Chair of Brewing and Beverage Technology, TUM School of Life Sciences Weihenstephan, Technische Universitaet Muenchen, Weihenstephaner Steig 20, 85354 Freising, Germany 2 Brewery C. Wittmann OHG, Laendgasse 50, 84028 Landshut, Germany 3 HVG Hopfenverwertungsgenossenschaft e.G. Kellerstrasse 1, 85283 Wolnzach, Germany Dry hopping is a traditional brewing technique that has undergone a resurgence in popularity in recent times. Dry hopping referrers to the addition of hops in the cold side of the brewing process, as opposed to the more common approach of adding hops exclusively to the wort during the boil. This minimizes the loss of essential oils, which normally evaporate during the boil, resulting in aroma close to that of the original hops. The subject of this study was a comparison of beers dry hopped in three different batch sizes. This is the first study to evaluate whether laboratory scale trials, which are commonly used for recipe development, produce comparable results when the recipe is scaled up to larger volumes. To facilitate this comparison one reference beer (RB) was dry hopped in three different scales. The industrial scale (IST) consisted of 14100 L, while the semi industrial scale (SIST) was 800 L and the laboratory scale (LST) was 17 L. Hop additions were calculated by weight (100 g pellets per hL beer). The hop oil concentration in the dry hopped beers as well as the RB were measured using headspace solid-phase micro extraction-gas chromatography-mass spectrometry. The substances quantified were preselected using gas chromatography-olfactometry trials during which aroma active hop volatiles were identified in the hop pellets and in the beers. Additionally, other known hop volatiles were quantified in the beers. The analytical results were correlated with the results from a trained tasting panel. The results show that mass transfer rates varied significantly between the different scales and significant differences were detected by the tasters (ANOVA with Fisher test LSD, significance level α=0.05). The normalized analytical results from this study are shown in figure 1. Overall the analysis values of the LST were higher with the exception of the “general impression” tasting attribute which was highest in the IST. Based on the results from this study it is concluded that laboratory scale dry hopping is not necessarily comparable to dry hopping on an industrial scale. Figure 1: Correlation of the tasting results and the aroma compound concentrationsa . The values have been normalized with lighter fields representing relatively low values and darker fields indicating relatively high values. RB: Reference beer (not dry-hopped), LST (laboratory scale trials), SIST (semi industrial scale trial), IST (industrial scale trial) Keywords: beer, hops, gas chromatography, scale up, sensorial evaluation
Article
In 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.
Article
Full-text available
Beer flavour and aroma depend mostly on the hop variety used in the brewing process. For this reason it is of crucial importance for brewers to be certain about the botanical origin of the hop variety. Metabolic fingerprinting is one of the approaches that can be used for determination of the botanical origin of many agricultural and food products. The aim of the current work was to differentiate between the five most important hop varieties in Slovenia. Gas chromatography, high-performance liquid chromatography (HPLC) and Fourier transform infrared spectroscopy were carried out in combination with three different chemometric methods – principal component analysis, regularized discriminant analysis and hierarchical clustering – on 121 hop samples. The chemometric classification of the hop varieties was obtained with nearly 100% success. The best results were obtained with GC and HPLC data, within one year of harvesting. Copyright © 2016 The Institute of Brewing & Distilling
Chapter
Commercial hops have approximately the following percentage composition: 1. Water 10·0 2. Total resins 15·0 3. Essential oil 0·5 4. Tannins 4·0 5. Monosaccharides 2·0 6. Pectin 2·0 7. Amino acids 0·1 8. Proteins(N×6·25) 15·0 9. Lipids and wax 3·0 10. Ash 8·0 11. Cellulose, lignin, etc. 40·0 100·0
Chapter
Microorganisms are used in many facets of the food industry. Desired alterations of food by microorganisms are referred to as fermentations, regardless of the type of metabolism. By definition, fermentation is the anaerobic breakdown of an organic substance by an enzyme system, in which the final hydrogen acceptor is an organic compound. Hence, the aerobic oxidation of alcohol to acetic acid in vinegar production is not a true fermentation. Hence, for our purposes these alterations of foods are called food conversions. Since the enzyme systems of the microorganisms catalyze the changes in foods, for some reactions it is advantageous to use purified enzymes separated from the microbial cells.
Chapter
Humulus lupulus var. neomexicanus grows in the semi-arid climate of Central Colorado. Its production of essential oil shows a characteristic seasonal dependence. This has been observed over two vegetation periods when the essential oil from the strobiles was isolated by steam distillation. The main components of the essential oil were identified by GC and GC-MS. More than 40 different components were detected, including mono-terpene hydrocarbons and alcohols, ketones, methyl esters of saturated and unsaturated carboxylic acids; in addition, esters of short chain acids with monoterpene alcohols and sesquiterpene hydrocarbons were found. Although the typical and chief scent of the neomexican hops strobiles is that of mango (Mangifera indica) fruits, the main components of the essential oil resemble those of the hop varieties already analyzed.
Article
Terpenoids are all derived from the intermediary metabolite isopentyl pyrophosphate. Terpenoids in beer derive mainly from hops. They impart important organoleptic properties to beer. Some are metabolized by yeast during fermentation to other terpenoid compounds. Yeast ' s ergosterol biosynthetic pathway also comprises intermediates that can potentially serve as precursors to important terpenoids such as farnesol, geraniol and linalool. Attempts to manipulate this pathway for enhanced terpenoid production are now proving successful. One terpenoid in particular (farnesol) has attracted particular attention since it has been demonstrated to have a wide spectrum of desirable properties including: anti-tumour, antioxidative, antifungal and antibacterial effects. Farnesol has been shown to act synergistically at low levels with other compounds/ cellular components in some experimental systems. For prevention of oxidative stress or carcinogenesis and tumor development, the required doses of farnesol or geraniol could never be provided by the consumption of beer. However, the farnesol obtained by beer drinking could play a very useful part in antibacterial and some antifungal therapies. A possible role for farnesol in prevention of Parkinsonism warrants further investigation.
Article
The potential of four selected tropical vegetables, Grongonema latifolium (Utazi), Vernonia amigdalina (Bitter leaf), Azadirachta indica (Neem) and Garcinia cola (Bitter Kola) as substitutes for hops in tropical beer brewing were evaluated. The vegetables were processed into powder by drying at 50°C for 24 hours (such that they maintained their original colour) and then cooled in dessicator before milling in a hammer mill. Proximate analysis showed that these vegetables had protein and crude fibre values comparable to those of commercial hops. Fat content values were however much higher than those for hops with Grongonema latifolium having the highest values of 19.10%. Garcinia cola with a total resin value of 8.24% and an essential oils value of (1.16ml/ 100g) had values which were significantly different from those of hops. The other three had values comparable to those for hops. Bitterness levels were high when the vegetables were extracted with organic solvents, than with distilled water. These values however decreased, the longer the storage period. Losses in bitterness were more when the vegetables were stored at ambient temperature than when they were stored at refrigeration or freezing temperatures. Losses in bitterness were more for water extracts than for organic solvent extracts.
Chapter
A number of unsaturated organic compounds have been determined by coulometric bromination. This method has been used successfully to titrate such compounds as styrene, monochlorostyrene, allyl alcohol, vinyltoluene, divinylbenzene, N-vinylpyrrolidone, vinylbenzylmethylammonium chloride, and other similar compounds. It can be used to determine micro-amounts of such compounds, but has proved equally useful for the determination of assay amounts. It has also been used to determine bromine numbers and iodine numbers of petroleum and natural products. New instrumental techniques have been developed simultaneously with new applications to make possible more rapid and convenient methods of analysis. A commercial constant-current source covering a current range of 4.82 to 193.0 ma is used in conjunction with an automatic potentiometric end-point detection device designed specifically for this purpose. It does not require a predetermined end-point potential and requires only two preliminary adjustments prior to titration. A redesigned cathode chamber provides a convenient way of emptying and filling the chamber with fresh electrolyte. Coulometric bromination is a sensitive, accurate, and convenient method of analysis for unsaturated organic compounds. It is more sensitive and selective than the conventional bromination methods, and, through automation, provides a convenience and saving of time valuable in laboratory use.
Article
Using a distillation-extraction technique, a commercial wort, both before and after hopping, was analysed by GLC for the presence of volatile compounds contributed by hops. The hopped wort contained at least 0·32 p.p.m. of volatile hop constituents which is probably sufficient to influence flavour. Most of these belonged to a group of water-soluble compounds which have not previously been detected in worts or beers.
Article
Extraction of hops with liquid carbon dioxide at ambient temperature provides an attractive means of producing hop extracts which are rich in α‐acids and free from hard resins, polyphenols, pigments and residual organic solvents. The resulting yellow extracts give beer with a clean bitter flavour when they are added during wort boiling. Manufacturing costs using the process are likely to be substantially less than in a conventional hop extraction plant. 1977 The Institute of Brewing & Distilling
Article
Gas chromatography of the head space was used to follow the evolution of hop aroma under different conditions of storage. Aroma from fresh hops contains mainly myrcene, which disappears as the hops get older. Meanwhile new, more volatile substances are formed, especially by degradation of the well-known α- and β-acids; when hops are kept in closed storage the aroma therefore soon takes a composite character. When the formed volatiles are allowed to escape, the aroma of hops becomes poorer with age, to disappear almost completely in the end. Twenty-five compounds have been identified in the more volatile fraction of hop extracts.
Article
Analysis of the essential oils from a large number of hop samples, using a combination of gas-liquid partition chromatography and adsorption chromatography, has shown that the oil content is affected by numerous factors including the variety of hop, the conditions during its growth and the treatment received by the cones after picking. Both over-drying and deterioration during storage appear to cause a preferential loss of the more volatile constituents. The total oil can be fractionated into hydrocarbon and oxygenated fractions, and the composition of each fraction would appear to be determined at least in part by varietal factors. It is confirmed that the proportions of myrcene and humulene in the hydrocarbon fraction are related inversely one to the other and can be correlated with the composition of the α-acids and of the β acids present in the hop resins. The biosynthetic implications of these findings are discussed.
Article
Changes in resin components and brewing value of several varieties of hops stored at two temperatures have been examined. Different varieties and temperatures of storage gave rise to significant changes in resin and oil composition, but these variables had little effect on bittering capacity.
Article
Appreciable amounts of α and β acids have been found in the essential oil obtained by steam distillation of hops.
Article
When a column containing powdered hops is extracted with liquid carbon dioxide, chromatographic separation of hop components occurs. They are extracted in the order essential oils, β-acids, α-acids; and the separation is enhanced when finely milled hops are extracted. Early fractions (∼0·5 hour) contain a high proportion of the available essential oils when hops are extracted at −20°C and such extracts are suitable as a replacement for dry hops. Fractions can be obtained from extractions at ∼7°C which are rich in α-acids and contain low levels of β-acids. Small amounts of fats and waxes are normally present in fractions collected towards the end of a run when seeded hops are extracted.
Article
Beer spoilage organisms added to hop oil emulsion rapidly die. Thus the emulsion is not a potential source of contamination of beer. However, the antimicrobial activity of the emulsion is insufficient to retard spoilage of beer contaminated from other sources.
Article
Pellets made from powdered Wye Target hops lost both α-acids and essential oil appreciably less rapidly than did cone hops during storage at ambient temperature for up to 2 years. Pelleting Wye Target hops is more effective than cold storage of cone hops in minimising losses of α-acids and maintaining brewing value. There are differences in the rate of loss of α-acids from pellets obtained when hops from a single growth of Wye Target hops were processed by four different processors. Cold storage of pellets from two processors resulted in a loss of just 5% of their initial α-acids after 27 months.
Article
Preliminary separation of hop oil (from Humulus lupulus L. var. Bullion) by physical and chemical methods, followed by programmed gas-chromatography analysis of the individual fractions, revealed the presence of approximately 200 components. The hydrocarbon fraction (70% of the total oil) contained myrcene (30%), caryophyllene (20%), and humulene (40%), plus some 20 minor componentl (10%). The oxygenated fraction contained a complex mixture of alcohols (2-methys butanol, linaloöl, nerol, geraniol, nerolidol, etc.), carbonyls (methylnonyl ketone and numerous other methyl ketones, citral and other aldehydes), and esters of carboxylic acids having straight chains, branched chains and unsaturated straight and branched chains. Most of the identifications are based on gas chromatographic retention times and are tentative.
Article
Examination of a wide range of hop varieties showed that the percentage loss of α-acid in storage was related to the essential oil content of the samples. Seedless hops, having higher oil contents, lost more α-acid than seeded hops of the same variety. The variety Bullion grown for isomerized extract manufacture should be picked 7–10 days earlier than normal to minimize loss of α-acid before processing.
Article
Methyl geranate has been identified with some certainty in oil from Bullion hops by comparison of infra-red absorption and mass spectral patterns with those of authentic methyl geranate. It has also been found that methyl geranate varies considerably in concentration in oils from different varieties, being almost completely absent from some varieties.
Article
The stability of hop essential oil in beers, in hops and in aqueous emulsions has been investigated. Hop character of beers treated with hop oil emulsion has stability on pasteurization and storage similar to that of dry hopped beers. When bottled with high levels of headspace air, beers lose hop character. Beers dry-hopped with stored hops or with hops damaged during pelleting tend to develop sulphury flavours. However, hop oil emulsions prepared from such hops give rise to a sound hop character in beer. Hop oil emulsion produced by the new process shows good stability physically, chemically and biologically, particularly when mechanically homogenized and stored under an inert atmosphere. The extent of any chemical alteration due to contact with air may be estimated spectrophotometrically.
Article
Improved equipment for producing hop oil emulsions by steam distillation at low temperature allows easier operation. In addition, a lower operating pressure results in a more efficient and less costly extraction. Emulsions obtained from similar batches of hops using both the new and older designs of hop extractors could not be distinguished by instrumental means or by a multiple comparison taste test.
Article
The main cost implications of the principal brewing materials as they relate to identifiable, compositional and transformational formulations are elaborated. The relationship of plant design in regard to these considerations is discussed.
Article
The mechanization of hop picking has led to a study of techniques for harvesting experiments by machine. An investigation of the accuracy of machine picking compared with hand picking, for this purpose, is described. It was found that variability was approximately the same for both picking methods, and treatment responses were similar.
Article
A flame-photometric sulphur detector was used to identify, measure and determine the sources of the sulphur volatiles produced during the commercial processing of British ale and lager. Dimethyl sulphide was the main sulphur volatile present in malt but traces of hydrogen sulphide, diethyl sulphide, and dimethyl disulphide were also detected. Hops contained hydrogen sulphide, methyl mercaptan, dimethyl sulphide, diethyl sulphide, methional and dimethyl disulphide. Most of this material extracted into commercial worts was driven off during boiling. Brewing yeasts produced only traces of organo-sulphur volatiles both in laboratory fermentations of wort and during the processing of commercial ales and lagers. In contrast, brewery bacteria, particularly wort spoilage organisms, could generate dimethyl sulphide and sometimes traces of other sulphur volatiles in laboratory cultures. t-Butyl mercaptan was the only organo-sulphur volatile detected in significant concentrations during the primary fermentation and conditioning of commercial beers and this was attributable to the activity of wort-spoilage bacteria. Attempts to identify a volatile compound causing ‘sulphury’ smells in beer were unsuccessful but there was some evidence that it might not contain sulphur.
Article
Present knowledge on the usage of hops is reviewed, and some outstanding problems are discussed in the light of likely changes in methods of processing.
Article
The aromatic constituents of hops have been analysed by gas chromatography. The essential oil comprises a mixture of hydrocarbons and of oxygenated materials, these two main fractions being readily separated by chromatography on silica gel. The hydrocarbons, which account for 70–80% of the total oil, comprise mainly myrcene, caryophyliene and humulene in proportions varying according to the source. The more complex oxygenated fraction contains considerable amounts of esters of at least 12 fatty acids-both straight and branched chain-containing four to 10 carbon atoms. As this oxygenated material distils very rapidly in steam it is likely to be absent from beer prepared according to normal hop-boiling conditions.
Article
Two recently published papers which report a relationship between certain fractions of hop resin and hop oil are discussed. It is pointed out that the choice of samples is inadequate to justify the conclusions drawn concerning the nature of this relationship.
Article
Hops in which the essential oil content has been reduced by steam distillation under vacuum lose α-acid on storage more slowly than do untreated hops.
Article
The precursor of dimethyl trisulphide (DMTS) in hops is destroyed by sulphur dioxide during kilning, but then re-forms slowly during storage. A redox mechanism is suggested and S-methyl-cysteine sulphoxide is postulated as the DMTS-precursor. The effect of DMTS on beer flavour is described. The flavour threshold value for DMTS in a commercial beer has been found to be 0·10μg/litre.
Article
The examination of undried Fuggles hops picked at intervals throughout the ripening period revealed that the total oil content of the samples rose throughout ripening, the production of hydrocarbons far exceeding that of the oxygenated compounds. The amounts of both myrcene and humuiene increased but, whereas the proportion of myrcene in the hydrocarbon fraction of the oil rose, that of humuiene fell throughout. The composition of the oxygenated fraction of the oil showed little apparent change. The drying of hops always reduced the amount of essential oil, usually without noticeably affecting its composition. Occasionally, however, drying caused a change in composition suggesting the occurrence of oxidation.
Article
During prolonged storage there is a reduction in the bittering potential of commercial samples of pellets made from either powdered Northern Brewer or Styrian Golding hops. These losses are particularly pronounced for Northern Brewer pellets stored at ambient temperature in ruptured packs. Hop pellets can also lose substantial quantities of essential oil during prolonged storage at ambient temperature and usually develop marked off-aromas. Such pellets are clearly unsuitable for dry hopping beer or for late additions to the copper. Beers brewed using pellets which have been stored warm usually have shorter shelf-lives than similar beers brewed using pellets which have been stored chilled. Changes in brewing performance can be minimized by storing hop pellets in sound packs at temperatures below 12 °C. Experience on the commercial scale has shown that whole hops stored at ambient temperature appear to lose up to 21% of their initial bittering value over a period of 18 months.
Article
Examination of the non-saponifiable constituents of the oxygenated fraction of hop essential oil has revealed the presence of 2-methyl butanol, linalool, methylnonyl ketone, methylundecyl ketone, geraniol, and the mono epoxides of caryophyllene and humulene as major constituents, together with three unidentified carbonyl compounds. Many other minor constituents are also present. Although geraniol is a major constituent of the non-saponifiable fraction, only traces of the free alcohol are present in the original oil.
Article
Gas chromatographic analysis of the headspace vapour of beer permits rapid measurement of the concentration of myrcene and the principal volatile alcohols, esters and carbonyl compounds in beer. In some cases the results obtained can be correlated with differences in flavour associated with changes in brewing procedure. The strength of the hop aroma of beers which had been dry-hopped, or to which hop oil had been added, was broadly reflected by the content of myrcene, which varied from 7 to 120 μg. per litre. A similar range was found in wort, the content depending on the conditions of boiling. However, the major part of this was lost during fermentation.
Article
Samples of hop oil were isolated from a number of different samples of sulphured and unsulphured hops using the recommended Institute of Brewing analytical procedure. Gas chromatographic analysis of these oils using a flame photometric sulphur detector shows that sulphuring causes reduction in amount or even elimination of some of the sulphur compounds. This provides a convenient technique for determining whether or not hops have been sulphured.
Article
Hop oil was investigated by gas chromatography coupled to a mass spectrometer. Almost all substances were obtained by preparative gas chromatography in amounts sufficient for N.M.R. spectral identification. Hop oil was separated into hydrocarbon- acid- alcohol- and ketone-containing fractions using adsorption chromatography, saponification, alkaline extraction and extraction with Girard T reagent. Fifty-three substances were identified of which sixteen have not been recorded previously as occurring in hop oil.
Article
Small amounts of the methyl geranates occur in the essential oil of hops although the major methyl C10 unsaturated esters are straight chain compounds.
Article
Comparison of Fuggle hops with low and normal seed contents has shown that “seedless” hops had α acid contents approximately 20% higher than seeded hops. There was no corresponding increase in β resin content. The mature “seedless” hops had almost twice as much essential oil as the mature seeded hops. Resin and oil syntheses in the seeded hops and resin synthesis in the “seedless” hops were complete by about the same date but oil synthesis in the “seedless” hops was not complete until I week later.
Article
Gas chromatography of the oxygenated constituents of hop oil indicated the presence of a number of high boiling point non-saponifiable compounds in addition to the previously recognized constituents. Methyl geranate appears to be the principal ester present in the oil.
Article
A distillation method using a modified version of the Connery and Wright technique or a B.P. still and measurement of the oil fraction by volume is recommended for the determination of the essential oil content of hops and hop powders.