Hop (plant)

The hop (Humulus) is a small genus of flowering plants, native to the temperate Northern Hemisphere. The female flowers, commonly called hops, are used as flavoring and stabilizers during beer brewing. The hop is part of the family Cannabaceae, which also includes the genus cannabis (also known as hemp).

Although frequently referred to as the hop vine, it is technically a bine; unlike vines, which use tendrils, suckers, and other appendages for attaching themselves, bines have stout stems with stiff hairs to aid in climbing. It is a perennial herbaceous plant which sends up new shoots in early spring and dies back to the cold-hardy rhizome in autumn. Hop shoots grow very rapidly and at the peak of growth can grow 20–50 cm per week (1 to 3 inches per day). Hop bines climb by wrapping clockwise around anything within reach, and individual bines typically grow between 2 to 15 m (6.5 to 50 feet) depending on what is available to grow on. The leaves are opposite, with a 7–12 cm (2 3/4 to 4 3/4 inch) Petiole and a cordate-based, palmately lobed blade 12–25 cm long (4 3/4 to 10 inch) and broad; the edges are coarsely toothed. When the hop bines run out of material to climb, horizontal shoots sprout between the leaves of the main stem to form a network of stems wound round each other.

Species
There are three species, one with five varieties: Brewers' hops are specific cultivars, propagated by asexual reproduction.
 * Humulus japonicus (syn. H. scandens). Asian Hop. Leaves with 5–7 lobes. Eastern Asia.
 * Humulus lupulus. Common Hop. Leaves with 3–5 lobes. Europe, western Asia, North America.
 * Humulus lupulus var. lupulus. Europe, western Asia.
 * Humulus lupulus var. cordifolius. Eastern Asia.
 * Humulus lupulus var. lupuloides (syn. H. americanus). Eastern North America.
 * Humulus lupulus var. neomexicanus. Western North America.
 * Humulus lupulus var. pubescens. Midwest North America.
 * Humulus yunnanensis. Yunnan Hop. Leaves with 3–5 lobes, densely hairy below. Southeast Asia (endemic in Yunnan, China).

History
The first documented instance of hop cultivation was in 736, in the Hallertau region of present-day Germany (which is today the most important production centre with about 25% of the worldwide production), although the first mention of the use of hops in brewing was in 1067 by Abbess Hildegard of Bingen. Hops were introduced to British beers in the early 1500s, and hop cultivation began in the present-day United States in 1629.

Today, the principal production centres for the UK are in Kent (which produces Kent Golding hops) and Worcestershire, and Washington state for the USA; other important production areas include Belgium, as mentioned Germany and the Czech Republic. Other major areas of production include Xinjiang (China), Tasmania (Australia), the Lublin area (Poland) and Chuvashia (Russia). New Zealand is a leading centre for organic hop production.

Until mechanisation (in the late 1960s for the UK), the need for massed labour at harvest time meant hop-growing had a big social impact. Many of those hopping in Kent were Eastenders, for whom the annual migration meant not just money in the family pocket but a welcome break from the grime and smoke of London. Whole families would come down on special trains and live in hoppers' huts for most of September, even the smallest children helping in the fields. In Kent, hops areas had Oast houses built for drying the hops; many now are converted to homes. The image of Cockney hoppers beneath the blue September skies of the Battle of Britain in 1940 has become part of British national mythology. Romany travellers were another very large group among the hoppers.

Propagation and pests
The European Hop is propagated either by nursery plants or by cuttings. These are set in "hills", formed by digging holes in the spring, which are filled with fine leaf mould. The density of the holes varies from 3–5 holes per m². One, two, or three plants are put in each hill; although, if hops are designed to be raised from cuttings, four or five of these, ranging from 7 to 10 cm (3–4 inches) in length, are planted 3–5 cm deep in fine leaf mould.

Hop growing, though profitable when it succeeds, is risky, with several significant insect pests causing damage, including the European Corn Borer Ostrinia nubilalis and the Hop froghopper Aphrophora interrupta. Hop gardens on chalky soils are particularly subject to damage. In June and July, the hops are liable to be damaged by an aphid, Myzus humuli. This insect, however, does not endanger the growth of the plant, unless it is already in a weak state from root damage by the larvae of the ottermoth, Phalaena humuli. The roots are also attacked by the larvae of Common Swift, Ghost Moth and Orange Swift. The foliage is sometimes eaten by the larvae of other Lepidoptera including Peacock Butterfly, Angle Shades, Currant Pug, Emperor Moth, The Gothic and Hebrew Character.

Harvest
At the end of the first year it becomes necessary to put poles into the hills, around which the bines reared from plants are wound; at the expiration of the second year, full-sized poles, from 5–6 m long, are set (though the hop bines will run to the height of 15 m) in the proportion of two poles to each hill, and a similar number of hop-plants are fastened loosely round each pole, by means of withered rushes.

In the northern hemisphere, hops begin to flower about the latter end of June or the beginning of July, at which point the poles are now entirely covered with foliage, and the pendent flowers are appearing in clusters. The hops themselves, which are the scaly seed-vessels of the female plants, are picked off by hand when the seed is formed around the end of August; for this purpose the poles are often taken down with the plants clinging to them. The seed-vessels are then dried, exposed to the air for a few days, and packed in sacks and sent to market.

Production
The 2005 world production of hops according to FAOSTAT was as follows;
 * 1)  Germany 29,000 tonnes
 * 2)  USA 26,180 tonnes
 * 3)  China 20,000 tonnes
 * 4)  Czech Republic 6,800 tonnes
 * 5)  Poland 3,355 tonnes
 * 6)  Australia 2,000 tonnes
 * 7)  North Korea 2,000 tonnes
 * 8)  UK 2,000 tonnes
 * 9)  Slovenia 1,500 tonnes
 * 10)  France 1,400 tonnes

The total world production for 2005 was 102,216 tonnes.

Beer
Hop resins are composed of two main acids: alpha and beta acids. Alpha acids have a mild antibiotic/bacteriostatic effect against Gram-positive bacteria, and favours the exclusive activity of brewing yeast in the fermentation of beer. The flavour imparted by hops varies greatly by variety and use: hops boiled with the beer (known as "bittering hops") produce bitterness, while hops added to beer later impart some degree of "hop flavour" (if during the final 10 minutes of boil) or "hop aroma" (if during the final 3 minutes, or less, of boil) and a lesser degree of bitterness. Adding hops after the boil, a process known as "dry hopping", adds hop aroma, but very little bitterness. The degree of bitterness imparted by hops depends on the degree to which otherwise insoluble alpha acids (AAs) are isomerised during the boil, and the impact of a given amount of hops is specified in International Bitterness Units. Unboiled hops are only mildly bitter. Beta acids do not isomerise during the boil of wort, and have a negligible effect on beer flavour. Instead they contribute to beer's bitter aroma, and high beta acid hop varieties are often added at the end of the wort boil for aroma. Beta acids oxidise and oxidised beta acids form sulphur compounds such as DMS (dimethyl-sulfide) that can give beer off-flavours of rotten vegetables or cooked corn.

"Noble hops" are low in bitterness and high in aroma, and traditionally consist of four central European cultivars, 'Hallertauer Mittelfrueh', 'Tettnanger', 'Spalter', and 'Saaz'. They contain high amounts of the hop oil humulene and low amounts of alpha acids cohumulone and adhumulone, as well as lower amounts of the harsher-tasting beta acids lupulone, colupulone, and adlupulone. Humulene imparts an elegant, refined taste and aroma to beers containing it. These hops are used in pale lagers.

English ales use hop varieties such as Fuggle, Golding and Bullion. North American varieties include Cascade, Columbia, and Willamette. Certain beers (particularly the highly-hopped style known as India Pale Ale) can have high levels of bitterness.

Flavours and aromas are described using terms which include "grassy", "floral", "citrus", "spicy", and "earthy".

Medicinal use
Hops have long-established and well-studied medicinal properties and uses, although new uses and properties are also being explored. Two of the many medically active ingredients in Hops are humulene and lupuline.

Dried female buds have a high methylbutenol content, which has a mild sedative effect on the central nervous system; it is used in the treatment for insomnia, stress and anxiety. If one has trouble getting sleep, hop tea before going to bed may help, though a quantity of beer has similar results.

Hops' antibacterial qualities also stimulate gastric juice production.

Hops have been studied for anti-viral properties and antimycobacterial properties. They also contain numerous various flavonoids, and they have been studied for containing Estrogen precursors as well.

Fibre
The stem is flexible and very tough, with a tenacious fibre that has been used in some cases to make cloth and paper. It may be noted that hops are closely related to hemp, which is also used for fibre.

Julmust
Hops are an ingredient in Julmust, a carbonated beverage popular in Sweden during the month of December.

Other uses
Tender young hop shoots, which are only available for about three weeks during spring, were mainly eaten by the poor in medieval times, and were a substitute for asparagus. Only recently have they been rediscovered as a delicacy in parts of Germany, Belgium and England. They are served raw with vinaigrette, or boiled with fresh herbs or fried in batter. In the italian region of Veneto, they are called bruscàndołi and are used to prepare risotto or frittata.

Wild hops are also relished by cows, horses, goats, sheep, and pigs.

Another use for the hop bine once it has reached full growth is to be cut down and used as a decoration in public houses or in kitchens. In the old wives' tale, the hop bine is supposed to bring good luck. In some parts of Kent and Sussex there are signs alongside the road advertising the sale of hop bines. Because of fierce competition in the hop trade, some farms find that sale of bines for this purpose is better than selling the hops themselves, since a pint of beer only requires one and a half hops.

Hops has also been used to increase breast milk production between woman with a low milk supply.