humulus_lupulus

Humulus lupulus L. - Cannabaceae - hop, Hopfen

Perennial dioecious climbing herb, native from Europe to Central Asia, North America.

Value-determining components of hops are a resin fraction (15-25%) and an essential oil, the hop oil (0.3-1%).
http://de.wikipedia.org/wiki/Echter_Hopfen#Inhaltsstoffe

Humulone (α-lupulic acid) and Isohumulones are bitter-tasting compounds found in the resin of mature hops (Humulus lupulus). Those alpha acids collectively give beer its characteristic bitter flavor.
„During development from female inflorescences to cones, levels of α-acids, β-acids, desmethylxanthohumol, and xanthohumol gradually increased, while each hop variety exhibited individual accumulation rates. Furthermore, these compounds were present in leaves of fully grown hops as well. The study demonstrated that key compounds for flavor and potential beneficial health effects associated with beer not only reside in the glandular lupulin structures but also are distributed over various parts of the hop plant.“
[Formation and accumulation of α-acids, β-acids, desmethylxanthohumol, and xanthohumol during flowering of hops (Humulus lupulus L.)., De Keukeleire, J., Ooms, G., Heyerick, A., Roldan-Ruiz, I., Van Bockstaele, E., De Keukeleire, D., Journal of agricultural and food chemistry, Vol.51(15), 2003, 4436-4441]

β-Acids: „The follow-up products of lupulones, the hulupones and luputriones, own a particularly pleasant mild bitterness. But they are far less bitter, so that the bitter taste of beer is predominantly shaped by the humulone fraction.“
[Belitz, H. D., Grosch, W., Schieberle, P., Lehrbuch der Lebensmittelchemie. Springer-Verlag, 2008, 925]

„The volatile constituents from several varieties of Hops have been investigated by the direct loading of fresh plant tissue through GC-MS. The Saaz variety was distinguished among the examined varieties by its high content of β-farnesene. Hallertau was characterized by a low content of myrcene and a high content of humulenes. Shinshu-wase differed in its high content of myrcene and its low content of humulenes. Northern Brewer was rather close to Hallertau, whereas Yakima appeared to be closely related to Shinshu-wase. The myrcene content of hop oil was observed to correlate competitively with the total amount of humulenes, caryophyllene, and farnesene. 2-Methylbutyl isobutyrate accumulates in company with myrcene.“
[The constituents of hops (Humulus lupulus L.). VII. The rapid analysis of volatile components., Naya, Y., Kotake, M., Bulletin of the Chemical Society of Japan, Vol.45(9), 1972, 2887-2891]

„Application of aroma extract dilution analysis on the volatiles obtained from dried cones of Spalter Select hops grown in the German hop-growing area of Hallertau revealed 23 odorants in the flavor dilution (FD) factor range of 16−4096, 20 of which could be identified. On the basis of high FD factors, trans-4,5-epoxy-(E)-2-decenal, linalool, and myrcene were identified as the most potent odorants, followed by ethyl 2-methylpropanoate, methyl 2-methylbutanoate, (Z)-1,5-octadien-3-one, nonanal, (E,Z)-1,3,5-undecatriene, 1,3(E),5(Z),9-undecatetraene, propyl 2-methylbutanoate, 4-ethenyl-2-methoxyphenol, and 1-octen-3-one. Ten of the high-impact hop aroma compounds had previously not been identified as hop constituents and, in particular, 1,3(E),5(Z),9-undecatetraene has not yet been reported as a food odorant. In an extract obtained from fresh hops, in addition to the odorants found in dry hops, (Z)-3-hexenal was characterized as a further key odorant rendering an additional green aroma note to the fresh material.“
[Comparison of the most odor-active compounds in fresh and dried hop cones (Humulus lupulus L. variety spalter select) based on GC-olfactometry and odor dilution techniques., Steinhaus, M., Schieberle, P., Journal of agricultural and food chemistry, Vol.48(5), 2000, 1776-1783]

Photolysis of the iso-α-acids is particularly important to the process leading to the characteristic „skunk-like“ aroma of lightstruck or „skunky“ beer. The primary compound that contribute to this off-flavor is 3-methyl-2-butene-1-thiol (prenylthiol).
[Burns, Colin S., et al. „Mechanism for formation of the lightstruck flavor in beer revealed by time‐resolved electron paramagnetic resonance.“ Chemistry–A European Journal 7.21 (2001): 4553-4561]

„Application of aroma extract dilution analysis on the volatiles isolated from a Bavarian Pilsner-type beer revealed 40 odor-active constituents in the flavor dilution (FD) factor range of 16−2048, among which ethyl octanoate, (E)-β-damascenone, 2- and 3-methylbutanoic acid, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone showed the highest FD factor of 2048. After quantitation of the 26 odorants showing FD factors ≥128 by stable isotope dilution analysis and determination of their odor thresholds in water, odor acitivity values (OAVs) were calculated. The results indicated ethanol, (E)-β-damascenone, (R)-linalool, acetaldehyde, and ethyl butanoate with the highest OAVs, followed by ethyl 2-methylpropanoate and ethyl 4-methylpentanoate, which was previously unknown in beer. Finally, the overall aroma of the beer could be mimicked for the first time by recombining 22 reference odorants in the same concentrations as they occurred in the beer using ethanol/water as the matrix.“
[Identification based on quantitative measurements and aroma recombination of the character impact odorants in a Bavarian Pilsner-type beer., Fritsch, H.T., Schieberle, P., Journal of agricultural and food chemistry, Vol.53(19), 2005, 7544-7551]

„Extremely strong fruity, black currant-like aromas were detected in beers hopped with some U.S. cultivars. 4-Mercapto-4-methylpentan-2-one (4MMP) was supposed to be the main contributor to the fruity aroma, and the contents between cultivars were investigated. In hop pellets, a negative correlation between 4MMP concentration and copper ion content in hops was observed. 4MMP was detected only in U.S., Australian, and New Zealand cultivars, but no European ones, which are treated with copper-containing fungicides (Bordeaux mixture) and therefore have a high content of copper ions. The 4MMP content was highest in Simcoe cultivars, followed by Summit, Apollo, Topaz, Cascade pellets, and also differed between crop years.“
[Kishimoto, Toru, et al. „Comparison of 4-mercapto-4-methylpentan-2-one contents in hop cultivars from different growing regions.“ Journal of agricultural and food chemistry 56.3 (2008): 1051-1057]

3-sulfanyl-4-methylpentan-1-ol and 3-sulfanyl-4-methylpentyl acetate have a grapefruit-like and/or rhubarb-like odor, similar to that of Sauvignon Blanc. They contribute to the specific odor of beers produced with Nelson Sauvin, a unique hop cultivar bred and grown in New Zealand.
[Identification and Characteristics of New Volatile Thiols Derived from the Hop (Humulus luplus L.) Cultivar Nelson Sauvin., Takoi, K., Degueil, M., Shinkaruk, S., Thibon, C., Maeda, K., Ito, K., Tominaga, T., Journal of agricultural and food chemistry, Vol.57(6), 2009, 2493-2502]

„Hallertauer volatiles were dominated by sesquiterpene hydrocarbons (46.5-50.8%), mostly α-humulene (22.7-28.0%), (E)-caryophyllene (7.8-9.0%), and (E)-β-farnesene (4.6-5.7%), with lesser amounts of γ-muurolene (1.1-1.7%), δ-cadinene (1.9-2.3%), and γ-cadinene (1.1-1.5%). The monoterpene myrcene was also abundant (21.4-24.8%) as well as the oxygenated sesquiterpenoids caryophyllene oxide (2.2%) and humulene epoxide II (3.9-4.0%). Sesquiterpene hydrocarbons are often characterized as having spicy or woody odors (Jiroventz et al., 2006; Sant’Anna et al., 2007; Sádecká and Polovka, 2008) and Hallertauer hops have been described as earthy, spicy, and “noble” (Brew365).“
[Volatile components of aroma hops (Humulus lupulus L.) commonly used in beer brewing.,Nance, M.R., Setzer, W.N., Journal of Brewing and Distilling, 2(2), 2011, 16-22]

„Application of aroma extract dilution analysis (AEDA) on the volatiles isolated from a commercial Bavarian wheat beer (WB A) eliciting its typical aroma profile, best described by a clove-like, phenolic odor quality, revealed 36 odorants in the flavor dilution (FD) factor range from 16 to 4096. Among them, 2-methoxy-4-vinylphenol (clove-like) and 2-phenylethanol (flowery) showed the highest FD factors. AEDA of a second wheat beer (WB B), somewhat lacking the typical wheat beer odor note, revealed 32 odor-active components in the FD factor range from 32 to 8192. Among them, 2-phenylethanol, (E)-β-damascenone (cooked apple-like) and 3-methylbutanol (malty) were detected with the highest FD factors. Next, all odorants evaluated with an FD factor ≥32 were quantitated by stable isotope dilution assays in both beers, and the odor activity values (OAVs; ratio of concentration to odor threshold) were calculated. Thereby, ethanol, (E)-β-damascenone, 3-methylbutyl acetate, ethyl methylpropanoate, and ethyl butanoate showed the highest OAVs in WB A, followed by acetaldehyde, 3-methylbutanol, and dimethyl sulfide. In WB B, ethanol, (E)-β-damascenone, ethyl methylpropanoate, ethyl butanoate, and 3-methylbutyl acetate showed the highest OAVs. Whereas most aroma compounds were present in the same order of magnitude in both beer samples, in particular, 2-methoxy-4-vinylphenol and 4-vinylphenol (smoky, leather-like) were by factors of 13 and 15, respectively, higher in WB A. For the first time, the overall aroma of wheat beer (WB A) was successfully simulated on the basis of 27 reference compounds in their natural concentrations using water/ethanol (95:5; v/v) as the matrix.“
[Characterization of the key aroma compounds in two Bavarian wheat beers by means of the sensomics approach., Langos, D., Granvogl, M., Schieberle, P., Journal of agricultural and food chemistry, 61(47), 2013, 11303-11311]

Application of a stable isotope dilution assay for 4-methyl-4-sulfanylpentan-2-one to 53 different hop samples revealed 4-methyl-4-sulfanylpentan-2-one concentrations between <1 and 114 μg/kg (well above the odor th). High concentrations were associated with US varieties such as Citra, Eureka, Simcoe, and Apollo, whereas 4-methyl-4-sulfanylpentan-2-one was absent from traditional German and English varieties.
[Reglitz, Klaas, and Martin Steinhaus. „Quantitation of 4-methyl-4-sulfanylpentan-2-one (4MSP) in hops by a stable isotope dilution assay in combination with GC× GC-TOFMS: Method development and application to study the influence of variety, provenance, harvest year, and processing on 4MSP concentrations.“ Journal of Agricultural and Food Chemistry 65.11 (2017): 2364-2372]

The quantification of aroma-active components of the four Hallertau flavor hops Blanc, Hull Melon, Mandarina Bavaria and Polaris confirmed linalool, myrcene, geraniol, as well as 2-methylbutyric acid and 3-methylbutyric acid as important cross-variety flavor compounds. The pronounced fruity aroma of Hull Melon is based on high concentration of esters ethyl 2-methylpropanoate, ethyl 2-methylbutanoate and propyl 2-methylbutanoate. The characteristically fruity-minty aroma of Polaris is caused by 1,8-cineol, 3-methylbutyl acetate and methyl 2-methylbutanoate.
[Neiens, S. D., and M. Steinhaus. „3.1. 1.3 Objektivierung der Aromaeigenschaften wichtiger deutscher Flavour-Hopfen durch Quantifizierung von Schlüsselkomponenten.“ Leibniz-Institut für Lebensmittel-Systembiologie an der Technischen Universität München (Leibniz-LSB@ TUM): Bericht 2017 (2017): 23-25] https://www.leibniz-lsb.de/fileadmin/doc/PDF/lsb_jahresbericht_2017_web.pdf#page=27

A new flavor hop variety, “Furano K906901060 Go” (named “Furano Magical”) „…has 80-129 μg/kg of 4MSP in its dried cones, which is higher than the world’s current leading flavor hop varieties, such as Citra (37-114 μg/kg) or Simcoe (51-112 μg/kg). Beer that was late-hopped with Furano Magical had a characteristic tropical, mango-like flavor, with an aroma intensity that was stronger than that of beer hopped using Nelson Sauvin.“
[Koie, K., et al. „Development of the new flavor hop variety “Furano Magical”.“ in: Proceedings of the Scientific-Technical Commission: 27-33, 2019] https://www.lfl.bayern.de/mam/cms07/ipz/dateien/proceedings_stc_2019_monitor.pdf#page=27

„The hop (Humulus lupulus L.), a component of beer, is a sedative plant whose pharmacological activity is principally due to its bitter resins, in particular to the α-acid degradation product 2-methyl-3-buten-2-ol. The mechanism of action of hop resin consists of raising the levels of the neurotransmitter γ-aminobutyric acid (GABA), an inhibitory neurotransmitter acting in the central nervous system (CNS).“
[The sedative effect of non-alcoholic beer in healthy female nurses., Franco, L., Sánchez, C., Bravo, R., Rodríguez, A.B., Barriga, C., Romero, E., Cubero, J., PloS one, Vol.7(7), 2012, e37290]
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0037290

Kohl, F.G., Die officinellen Pflanzen der Pharmacopoea Germanica, t.30 (1891-1895)
http://www.plantillustrations.org/species.php?id_species=539209