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Humulus lupulus

Hemp Family [Cannabaceae]  

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24th Sept 2009, Swinton, Gtr M/cr. Photo: © RWD
The Hop cones form from the female flower after the separate male and female flowers (on the same plant) have flowered. The stem winds clockwise around any support.

24th Sept 2009 Swinton, Gtr M/cr. Photo: © RWD
The light-green cones hang downwards, each on their own stem. The leaves are coracle toothed.

24th Sept 2009 Swinton, Gtr M/cr. Photo: © RWD
The cones have several faint lighter-coloured veins.

24th Sept 2009 Swinton, Gtr M/cr. Photo: © RWD
There are four sepals behind the cones.

24th Sept 2009 Swinton, Gtr M/cr. Photo: © RWD
The inside of the cone is fairly secret.

24th Sept 2009 Swinton, Gtr M/cr. Photo: © RWD
The leaves, which may be either palmate, or nettle-shaped, come off a main stem in pairs at right-angles, the underside much lighter than the dark upper surface of the leaves.

24th Sept 2009 Swinton, Gtr M/cr. Photo: © RWD
The dark-green stems are angular, with reddish ridges which accommodate very short spines all pointing backwards to help it climb.

24th Sept 2009 Swinton, Gtr M/cr. Photo: © RWD
The upper surface of the dark-green leaves also has a rough one-way tactile texture.

17th May 2009, Bury, Gtr M/cr. Photo: © RWD
Goldings hops have light-green leaves. Neither flowers nor hop cones have yet grown. The number of lobes on a leaf of Humulus Lupulus varies from one, three, or five on the same plant, the larger leaves having five. (Humulus Japonica has five to seven-lobed leaves)

24th Sept 2011, Chesterfield Canal, Worksop, South Yorks. Photo: © RWD
Barges used to carry hops on the Chesterfield Canal for the Worksop & Retford Brewery, which closed in 1958 and was then taken over by Tennant's. The brewery was demolished in 1962 when Whitbread took over Tennant's. These hops are escapees from those barges; Worksop and Retford being on the same canal about 10 miles apart.

24th Sept 2011, Chesterfield Canal, Worksop, South Yorks. Photo: © RWD
The hops hang like grapes on alternate sides of a thin stem.

24th Sept 2011, Chesterfield Canal, Worksop, South Yorks. Photo: © RWD
The hops are very light in weight, almost paper-like. Leaves have large teeth; the underside being a much lighter green and with prominent veins (lower right).

24th Sept 2011, Chesterfield Canal, Worksop, South Yorks. Photo: © RWD
Some hop cones barely make the grade.

24th Sept 2011, Chesterfield Canal, Worksop, South Yorks. Photo: © RWD
An individual seed-cone (strobile) comprises several overlapping layers of extremely light-weight bracts. Most of the hop consists of air spaces between the scales.

1st Nov 2011, The Hop Vine PH, Burscough Bridge. Photo: © RWD
If the cone is pulled apart, many sand-sized grains of a yellow substance become visible and which are are coloured by the pigment Xanthohumol, which is yellow. These grains are not pollen. The grains contain a substance called 'Lupulin' but which is not a single substance but a waxy oleoresin containing a collection of differing compounds, including Lupulone and Humulone.

24th Sept 2011, Chesterfield Canal, Worksop, South Yorks. Photo: © RWD
The leaves of these particular Hops either have no lobes and are Nettle-leaved, or have three lobes, the central one being more rounded.

24th Sept 2011, Chesterfield Canal, Worksop, South Yorks. Photo: © RWD
The three-lobed leaves look similar in shape to those of Fig leaves.

24th Sept 2011, Chesterfield Canal, Worksop, South Yorks. Photo: © RWD
A typical three-lobed leaf. Note the clockwise twinning of the stalks.

Uniquely identifiable characteristics

Distinguishing Feature : The aromatic pale-green cones that hang downwards after flowering.

Not to be confused with: Hop Trefoil [a plant with similar name belonging to a different family]

Hop is a climber without tendrils, it climbs by wrapping itself clockwise around a supporting branch or stem of any other plants nearby aided by the stiff short backwardly directed spines on the stems. This mode of climbing is represented by the word bine; therefore it should be known as Hop bine, rather than Hop vine. Vines climb by the use of tendrils and suckers, which Hop bines lack.

Hop is dioecious, with male and female flowers on separate plants. The hops themselves are actually the fruits or seed-cones (more accurately strobiles) of the female flowers. The female flowers have numerous cream-coloured stigmas. The fruits (hops) are extremely light in weight for their size. Hops are aromatic if crushed. The male flowers are in panicles 7-10cm in diameter - the individual flowers are ~5mm across with five cream-coloured petals and five banana-shaped anthers. A female plant, when under stress, can temporarily for one year produce male flowers, but will revert to true female form the next season.

The stems are angled, with very short rough spines facing one way which helps it to cling on to whatever stems it is climbing up.

Hops are used as the main aromatic flavouring element in ales, beers, lagers, stouts, entires, porters and some other alcoholic drinks. It is hops which impart the bitterness to bitter. Fresh green cones are usually used for the best beers. There are many varieties grown commercially, especially in Kent, but also in other parts of the world especially for lagers.

Hops have been used as the bittering component to flavour beers since the 8th or 9th century. They also exhibit an anti-biotic and anti-septic effect which helps preserve the beer. Before hops were used, a wide variety of other herbs were used to flavour 'beer', such as Dandelion, Horehound, Burdock root, Marigold, Ground-Ivy, Heather, Bog Myrtle, Spruce, Bogbean, Broom, Stinging Nettle, Yarrow, Wood Sage, Mugwort, Horehound (the Marrubium vulgare type of Horehound rather than Black Horehound which smells repugnant!), and many others. It is still possible to obtain Spruce Beer in parts of Scandinavia and America, but, un-like hops which have a soporific effect reducing one to sleep before drinking too much, spruce has an up-lifting effect, and is probably more dangerous from a point of view of alcohol poisoning.

Other adjunct herbs such as Henbane, Deadly Nightshade!!, Common Juniper berries, Ginger, Caraway seeds, Aniseed, Bergamot, Horse Mint, Rosemary, Nutmeg or Cinnamon were sometimes added for extra flavouring, and indeed some are still used for speciality beers, although your author would prefer not to drink any brewed using Deadly Nightshade! [some of the others are also probably outlawed now].

The following is a list of all hop varieties grown commercially for the brewing trade: Czech Saaz, US Saaz, Tettnanger, German Tettnanger, Cluster. Styrian Gold, Suoper Styrian, Strisslespalt, Spalt Select, US Spalt, German Spalt, Kent Golding, US Hallertau, Perle, Progress, Liberty, US Hersbruck, German Hersbruck, Lublin, US Fuggle, British Fuggle, German Mittelfruh, Galena, Mt. Hood, Cascade, German Tradition, Huller, Willamate, Crystal, Challenger, Target, Pacific Gem, Brewer's Gold, Pride of Ringwood, Northern Brewer, Northern Brewer Hallertau, Columbus, Centennial, Nugget, Eroica, Chinook and Bullion. All have differing proportions of the main flavour components, both good and bad, many of which are shown below.

Apart from Hemp, Hop is the only (UK) member of the Hemp Family.

Myrcene is an olefin monoterpene that is contained in plants of Genus Myrcia (with no representation in the UK), Verbena, Hop, Hemp and Bay Laurel. It has a pleasant odour and is used in perfumery. Although myrcene has a high presence in hops, up to 30%, it is highly volatile and does not usually survive in the finished beer, although its degradation and oxidation products such as linalool, Geraniol and geranyl isobutyrate do. American hops have a higher content of Myrcene, and dry-hopping with these hops creates a characteristic citrus (like grapefruit) and pine aroma in beer, although this compound degrades fast within beer.

Linalool is a terpene alcohol with a floral slightly spicy smell found in many plants including the peel of citrus fruits and especially in Lavender and used as a scent in perfumery, soap and toiletries, and as an insecticide for fleas and cockroaches.

Farnesene is a green sesquiterpene found in the skin of Apples and is responsible for their greenness and odour. Damage to the fruit results in the release of Farnesene contained within cells, the subsequent oxidation of which turns the fruit brown. It acts both as an insect repellent and pheromone. Potatoes and other similar species synthesize Farnesene as an insect repellent. Farnesene is also volatile and degrades into innumerable other compounds during brewing and even when dry-hopped Farnesene does not contribute much to the flavour of beer. All three are present in both Hop and Hemp.

Humulene otherwise known as α-Humulene, is a caryophyllene, this time a mono-cyclic sesquiterpene. It is present in Hop and Hemp, contributing to their aroma, taste and bitterness. Humulene has a greater percentage in noble hops than does myrcene, but it too degrades during the boiling process in beer production, the oxidation products of which survive, imparting several desirable characteristic flavours to the finished beer. Most of the flavour in beer comes from dry-hopping which increases the humulene content after fermentation, where they may get converted into other substances. Caryophyllene, otherwise known as β-caryophyllene is a bi-cyclic sesquiterpene found in Hop, Hemp, Rosemary, Cloves, Caraway, Oregano and also contributes to the spiciness of Black Pepper. Amounting to between 5% and 15% in hops, the oxidation products of caryophyllene contribute to the herbal spicy flavour of beer.

All four of the above compounds, humulene, caryophyllene, farnesene and myrcene are present to various percentages in hops and contribute to desirable flavours, aromas and sensations in ales. These compounds constitute the major constituents of the essential oils of hops, of which there are over 300, including the terpene alcohol linalool at 1%. Linalool is used in perfumes, such as eau-de-cologne.

Related to Humulene and Farnesene are the Alpha-acids which is why Humulene is sometimes referred to as Alpha-humulene, whereas the Beta-acids are related to Caryophyllene, sometimes called Beta-caryophyllene for much the same reason. The alpha- and beta-acids are the resins in hops, as opposed to the essential oils mentioned above.



The alpha-acids humulone, cohumulone and adhumulone are present in hops. They are not very soluble in water, but during the wort boiling phase of brewing are and are converted to the much more soluble and bitter compounds cis-isohumulone and trans-isohumulone. The cis- and trans- forms of isohumulone are in chemical equilibrium and contribute much to the bitterness of beers. The alpha-acids isomerise into cis- and trans- forms during the brewing process. These iso-alpha acids (aka isohumulones)are responsible for the bitterness of beer. The alpha-acids also have an important antiseptic role in beer in preventing the unwanted growth of bacteria. Beta-acids also play an antiseptic role. The beta-acids lupulone, colupulone and adlupulone are also present in hops but are much less bitter than their alpha-equivalents, but with a harsher bitterness. However, they are not very soluble in beer and tend to precipitate out in the wort. Unlike alpha-acids they do not isomerise as much during the brewing process but they are partially oxidised to become delta-acids (hulupones). The products of oxidation of beta-acids do influence the taste and aroma of beer but to a much lesser extent, and are not present in hops themselves so have no representation here. Many brewers think beta-acids impart a negative factor in beer and try to limit the amount put in by prudent choice of hops.

Both cis- and trans-Isohumulone are formed in the brewing process, and are the result of boiling the largely insoluble (in water) humulone. Isohumulone is much more soluble in water and contributes much to the desirable bitterness to beers. Note that humulone has a six-membered ring, whereas the product Isohumulone has a 5-membered ring. Rather unfortunately, Isohumulone is very susceptible to cleavage into a pair of radicals when subjected to light in the presence of Riboflavin (vitamin B2), a yellow chromphore present in beer. These radicals then react with Cysteine, an amino acid which is also present in beer, to form a most un-desirable product, 3-methyl-but-2-ene-1-thiol, which is a sulfurous mercaptan (prenyl mercaptan) which imparts an un-pleasant and un-desirable musky flavour and aroma to the beer. The use of brown glass bottles prevents this, but not green. Beer sold in clear bottles is usually specially made using hydrogenated hop extracts which prevent this reaction occurring.

Prehumulone, Posthumulone, prelupulone and postlupulone are also acids found in hops. All the acids are fairly weak acids, having a pH of around 5.

minor Alpha-acids

minor Beta-acids

Prehumulone and Posthumulone are minor-constituent alpha-acids that still contribute towards the taste of ales. Prelupulone and Postlupulone are minor-constituent beta-acids.

Unlike alpha-acids beta-acids do not isomerise as much during the brewing process but they are partially oxidised to become delta-acids (hulupones). Hulupone is just one of the many oxidation products of beta-acids whilst in the brewing process; they are not present in hops. It is a quadruple lactone, others are not oxidised quite as much as is this.

  Xanthohumol is a prenyl chalconoid and yellow-coloured substance that is present in the yellow pollen grains to be within the female hop flowers (the hops) inside the glands near the centre. It is also present in the beer, and has anti-oxidant, anti-bacterial and anti-fungal effects. It is claimed to have health benefits.

The sesquiterpenes Cadinene, Muurolene and Selinene, which are also present in hops, may further contribute to the flavour of beer in ways not fully understood. Your Author has purposely avoided drawing the structure of these 3 similar sesquiterpenes because all three come in a variety of differing isomers but the source did not name them.

Hop varieties with a high α-acid content (which are used for cheap beers) include Brewers Gold, Cluster, Chinook, Eroica, Galena, Nugget, and Yeoman. Hops with a lower α-acid content (which have a stronger aroma and flavour qualities) include Fuggles, Goldings, Hallertauer, Saaz and Tettnanger.

Other varieties of Hops include the following: Admiral, Ahtanum, Amarillo, Apollo, Aquilla, Banner, Bramling Cross, Bravo, Bullion, Calypso, Cascade, Centennial, Challenger, Citra, Cluster, Columbia, Columbus, Comet, Crystal, Delta, First Gold, Galaxy, Glacier, Green Bullet, Herald, Horizon, Huller, Kent Golding, Liberty, Lublin, Magnum, Millennium, Motueka, Mt. Hood, Nelson Sauvin, Newport, Noble, Northdown, Northern Brewer, Olympic, Omega, Orion, Pacifica, Pacific Gem, Pacific Jade, Palisade, Perle, Phoenix, Pioneer, Peide of Ringwood, Progress, Riwaka, Santiam, Saphir, Simcoe, Sorachi Ace, Southern Cross, Spalter, Sterling, Sticklebract, Styrian Goldings, Summit, Sun, Super Alpha, Super Galena, Talisman, Target, Taurus, Tomahawk, Tradition, Ultra, Vanguard, Warrior, Willamette, Zenith and Zeus, although this still probably omits some hop varieties.

Hops deteriorate in storage. However, lambic brewers do what to most brewers would be anethema: they age the hops for several years before use, which changes the flavour profile and alters the bitterness profile. Lambic brewers use these aged hops primarily for their preservative properties.

Brewing Beer with Malt



Prenyl Mercaptan (aka 3-Methyl-But-2-ene-1-Thiol, or 3-MBT) is a potent musky smelling chemical that is (amongst other sulfur containing chemicals) responsible for the foul odour of beer that has been exposed to sunlight. It is a highly undesirable product that is not normally present in beer but is produced when beer has been exposed to ultraviolet light for extended periods and is one of the reasons why beer is supplied in brown bottles. It has an intense sulfurous, leek or onion-like odour and is responsible for the so-called 'sunlight' flavour of beers.

Both blue light and UV-B light activate the catalysis of IsoHumulene (which comes from the hops) by Riboflavin (Vitamin B2, which comes from both the Malt and the yeast) creating free radicals, one of which is 1,1-DimethylAllyl. This compound can remove a thiol group from the sulfur-containing amino acid Cysteine to become 3-MBT, which is one of the repugnant compounds responsible for 'lightstruck' beers. 3-MBT is very similar to several other thiols which are produced within the scent gland of Skunks, such as 2-Butene-1-Thiol and 3-Methyl-1-ButaneThiol.

Because the wavelengths of light which catalyse the undesirable chemical reactions occur in the blue-region of the visible spectrum and in the near ultraviolet (UV-B), green bottles will not block this radiation; the bottles must be of brown glass. Even after a pint has stood in bright-sunlight for only 10 minutes the 3-MBT can be detected by taste and by smell, although much may depend upon beer temperature and the amounts of Riboflavin (Vitamin B2, which is also a yellow dye with a yellowish-green fluorescence) and IsoHumulenes present in the beer and how dark or cloudy is the beer. The aroma threshold of 3-MBT is exceedingly low, being detectable by smell at concentrations of only 0.05ppm, so only an extremely small amount need be synthesized for it to affect the flavour. A 1 litre bottle need contain only 0.05 cubic millimetres of 3-MBT before it is detectable.

Some companies use Rho-IsoHumulenes and Tetra-HydroIsohumulenes (the latter are especially bitter) instead of IsoHumulenes in beer to impart bitterness to the beer. Although both Rho-IsoHumulenes and Tetra-HydroIsoHumulenes will also degrade in strong light, they will not degrade into 3-MBT. The rho-IsoHumulenes and TetraHydroIsoHumulenes are produced by chemically reducing the IsoHumulenes with Sodium Borohydride, NaBH4, a process that does not occur naturally whilst brewing. Such beers are made in chemical factories rather than breweries! They are probably those beers sold in clear bottles.

2,3-Butanedione, commonly called Diacetyl, is a toxic ketone. Diacetyl is a natural product of fermentation and imparts a usually undesirable buttery butterscotch flavour (butterscotch may itself contain no diacetyl) to beer if it is present in sufficient amounts (>70ppb). However, during the maturation period the yeast is able to absorb the diacetyl later such that the levels are imperceptible to taste (at below 70ppb). But when other factors come into play sometimes this is prevented from happening and a butterscotch flavour is imparted to the beer. In some beers this is acceptable, in others such as lager, it is not. The diacetyl comes from α-Acetolactate which is generated by yeast. To stop the diacetyl from forming in the first place some breweries introduce the enzyme α-acetolactyl decarboxylase to the brew which converts the α-acetolactate directly into acetoin bypassing the diacetyl stage. This eliminates formation of diacetyl and means that the brewery can shorten or entirely eliminate the maturation process. However, acetoin itself also has a buttery flavour. A further stage may result in 2,3-Butanediol being formed from the Acetoin.

Both diacetyl and acetoin are added in very small amounts to margerine to make them taste 'buttery', but since diacetyl is toxic there is a call for the deliberate addition of it to foodstuffs to be banned.


The aroma profile of beers is multi-dimensional and attempts to measure the various proportions (on a sliding 0-4 scale) of the following: Alcohol/Solvent, DiMethylSulfoxide (DMS), Other Sulfur, Cereal/Grainy, Malty, Woody, Fresh Hop, Grassy, Herbal, Spicy, Floral/Scented, Pear/Apple, Citrus Fruits, Soft Fruits and Tropical Fruits aromas.

The taste profile of beers is also multi-dimensional, attempting to determine the various proportions (on a sliding 0-6 scale) of the following tastes: Alcohol/Solvent, DiMethylSulfoxide (DMS), Other Sulfur, Cereal/Grainy, Malty, Woody, Fresh Hop, Grassy, Herbal, Spicy, Floral/Scented, Pear/Apple, Citrus Fruits, Soft Fruits, Tropical Fruits as well as extra items not in the aroma profile: Linger, Body, Astringent, Mouthcoating, Sour, Bitter and Sweet.

Various characteristics are undesirable, such as 'DMS' or 'Other Sulfur' smells. Woody your Author likes! Some beers taste a little like oak-matured whisky. Excellent! Strange that there is no mention of Peaty. Your Author likes peaty too!

  Humulus lupulus  ⇐ Global Aspect ⇒ Cannabaceae  

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Humulus lupulus

Hemp Family [Cannabaceae]  

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