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 long 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 up to 7-10cm in diameter - but 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 cones contain between 20 and 60 individual female flowers (count the styles on a female flower - there are between 20 and 60).
With hops grown for making beer it is essential to try and ensure that the female flowers on a female plant are not pollinated by the male flowers of a male plant. If the female is pollinated then the hops will grow seeds, which contain high levels of fatty acids leading to undesirable flavours in the beer produced from them. To reduce the risk of female plants being fertilised by male plants the male plants should not be grown in the same field.
In the variety of hops called 'cascade' the female plants can also produce some 'male' flowers - and whether they do or not is dependant upon many climatic conditions (such as temperature, sunlight, etc) in which the hops are grown. Some seasons the cascade hops will also produce male flowers, but other seasons they wont. However, when examined closely, these male flowers on cascade hops, judged by the genetic information in their genes, are all still female - their pollen is sterile, unable to fertilise the female flowers, so no seeds will be produced anyway, and the grower of cascade hops need have no fear.
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,
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,
Horse Mint, Rosemary,
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.
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
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,
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. β-caryophyllene has a clove-like scent emitted by Roses and Lavender, and is easily and quickly destroyed in a matter of yards when low concentrations of atmospheric pollutants like CO, NO2 and O3 are present in the air, which could help explain why Roses cannot be smelled in town gardens. It is also present in Common Juniper, Lesser Water-Parsnip and Hedge Woundwort amongst many others.
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 |
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.
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
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.
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, Agnus, Ahtanum, AlphAroma, Amarillo, Apollo, Aramis, Aquilla, Banner, Belma, Bramling Cross, Bravo, Bullion, Calypso, Cascade, Celeia, Centennial, Challenger, Citra, Cluster, Columbia, Columbus, Comet, Crystal, Delta, Equinox, Eroica, Falconer's Flight, First Gold, Galaxy, Galena, Glacier, Golding, Green Bullet, Hallertau, Helga, Herald, Herkules, , Hersbrucker, Horizon, Huell Melon, Huller, Jester, Kent Golding, Liberty, Lublin, Magnum, Mandarina Bavaria, Meridian, Merkur, Millennium, Mittelfruh, Mosaic, Motueka, Mt. Hood, Nelson Sauvin, Newport, Noble, Northdown, Northern Brewer, Nugget, Olympic, Omega, Orion, Pacifica, Pacific Gem, Pacific Jade, Palisade, Perle, Phoenix, Pioneer, Pride of Ringwood, Progress, Riwaka, Saaz, Santiam, Saphir, Select, Simcoe, Sorachi Ace, Southern Cross, Spalter, Sterling, Sticklebract, Styrian Goldings, Summit, Sun, Super Alpha, Super Galena, Talisman, Target, Taurus, Tettnanger, Tomahawk, Tradition, Ultra, Vanguard, Waimea, Wakatu, Warrior, Whitbread Goldings, Willamette, Zenith, Zeus, and Zythos although this list still probably omits some hop varieties.
Hops deteriorate in storage. However, lambic brewers do what to most brewers would be anathema: 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.
Some beers are put in oak casks where they acquire a woody or peaty taste due to a lactone in the wood called
Whisky Lactone aka the 3S,4S stereoisomer of cis-
3-Methyl-4-Octanolide (which can exist in two stereoisomers (the other being the 3R,4R stereoisomer which is not Whisky Lactone). Thus some beers can acquire a whisky-like woodiness which your Author craves, for his favourite beer called Yates Bitter (nothing to do with any wine lodge), which is brewed in Cumbria, did indeed taste like whisky (if not 1/10th as strong!). Unfortunately, Yates Brewery has ceased production, and even when it was in production, for the last ~20 years of brewing it lacked the woody taste, presumably because they had started putting it in metal casks (although they presumably could have thrown oakwood chips in to re-impart the woody flavour)! Whisky Lactone does not occur in Hops, but does in Oak wood, (along with the trans- isomer).
Contained within wood is another compound,
o-MethoxyPhenol)) which is found in wood and in wood smoke. This too smells of wood and has a woody taste. It can impart woody tastes to beer or whisky placed in oak barrels. Guaiacol is an oily yellow liquid which darkens upon exposure to air. Guaiacol is used as a precursor in the mass chemical synthesis of flavour compounds such as Eugenol and Vanillin. Guaiacol is also produced by a bacterium within the gut of locusts as they digest plant material and is one of the main pheromones which causes locusts to swarm.
β-Guaiene, a sesquiterpene, has a skeleton structure consisting of fused 7 and 5 membered rings as does Azulene. There are two other isomers of it,
δ-Guiaene which have their two double-bonds in differing places, but neither of these isomers are claimed to be present in
Hops. It is not related structurally to the similar sounding secondary metabolite Guaicol, described above. It is also found in many plants including Hop. This compound also imparts a characteristic woody smell and woody taste to beer. It was first isolated from Guiaiac Wood Oil which was extracted from the foreign plant Bulnesia sarmienta. All the Guaienes are used as fragrances and flavours to impart earthy, woody and spicy tastes and aromas to foodstuffs.
Brewing Beer with Malt
The above represent a small fraction of the compounds which might occur in the beer which the reader might be drinking at this moment. But there are so many other compounds not shown which might also be in the beer. The type of hops used has a large say in which particular compounds may be produced or are present in the beer, but a lot also has to do with the actual brewing process itself, and the compounds produced may undergo further physical, biochemical and chemical changes during brewing and fermentation. In addition there are changes which occur during subsequent storage in wooden barrels, steel casks or glass bottles and the environmental factors (such as storage temperature) which might produce further changes in composition. There are increasing trends amongst some brewers to circumvent some of these variable factors by adding fractionated hop oils with the required specific odour characteristics to the beer after fermentation. But then, why bother with fermentation, why not go the whole hog and add all the desired ingredients to water!
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.
AROMA & TASTE PROFILES OF ALES
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!