HOPS

Humulus lupulus L. (Cannabaceae).

First given its scientific name by Carolus Linnaeus in 1753, from European cultivated plants.

Native to Europe; possibly also native in the North America.

Life form: large annual vine, sometimes grown as a short-lived perennial (dying to roots each cold season) when an escape from cultivation.

Parts used: 'cones' or fruiting female inflorescences used in the brewing of beer.

Ploidy level: diploid.

Wild relatives

Humulus is one of two genera in the family Cannabaceae; the other genus is Cannabis. There are many similarities between cultivated hops and cultivated hemp (Cannabis sativa L.), including their graft compatibility.

There are three species in the genus Humulus. They are annual or perennial vines native to North America, south-east Asia and Europe. All species of Humulus are dioecious, with male and female flowers borne on different plants.

  • Humulus lupulus L. (the cultivated hop) is an annual or perennial species not known in the wild; it is thought to be originally native to both Europe and North America (American plants were previously known as Humulus americanus Nutt.).
  • Humulus japonicus L. (the Japanese hop), an annual species, is widespread throughout much of China and Japan, but nowhere else.
  • Humulus yunnanensis L. is a perennial wild species that we know little about; it occurs at high altitudes in south China, especially Yunnan province. There are a few herbarium specimens in museums, but no plants in commercial cultivation.

Hops are commercially important because they contain an a-acid that turns sweet ale into bitter beer and also acts as a preservative. essential oils add a unique flavour to the beer. The a-acid is a major component of soft resins found in the lupulin gland on the hop flower; these glands are more plentiful on female flowers than on male flowers, and so female plants are more prized by commercial growers. Humulus lupulus has the highest concentration of lupulin glands, and therefore is far more commercially valuable than Humulus japonicus or Humulus yunnanensis.

Origins of cultivation

The species of Humulus are all thought to have evolved from a common ancestor, originally from China. Although hop cultivation has not been recorded in the region, the use of malting technology (without hops to make ale) was common. The cultivation of hops appears to have begun further to the west.

The earliest written evidence of hop cultivation was in Germany in 736 AD, although it is believed that hops were cultivated in Babylon in 200 AD. Archaeological evidence corroborates the written evidence, as many hop fruitlets were found in ancient waterlogged sites throughout Europe.

Early uses

In Geek and Roman times, the shoots of young hops were eaten as a vegetable but hops were then only grown as a garden crop. A solution of hops was used as a wash for chronic ulcers and skin eruptions.

Written records show that ale was hopped and turned into beer in Bavaria in the 9th century; this happened later throughout north-west Europe and by the 13th century hops were widely known. In Britain before the Norman Conquest the Anglo-Saxons used ale (or perhaps beer), not wine, as an everyday drink. Almost the earliest written record of hops used in brewing in Europe comes from the Abbot Adalhard of Corvey in France in AD 822. For some reason he released grain millers from the labour of grinding malt and hops, there being few mills apart from those of grain millers. Later, of course, brewers, not millers, performed this process.

Without hops, all beer is more properly called 'ale', which is sweet and has a very short life. It is more like a sweetish soup and is a favoured food where the starchy origin is unpalatable or difficult to consume in other ways. Ale can be made of any high-starch vegetable, but is usually made of cereals, maize or even bananas. Such food (or drink) is still widely brewed in Africa, but is locally produced and consumed and rarely traded.

Transfer and spread

The cultivation of hops extended to north Germany, Bohemia and Flanders where they became commercially important in the 14th century, some 400 years after their introduction. The French were importing hops into Dieppe from the Netherlands and England in the late 14th century. The word 'Hoppe' was unknown in England before 1440, but there is evidence that the plant was introduced to England before 1400. Henry VIII banned the use of hops. He rightly thought that hops increased the alcohol content of fermented drinks, because with hops, beer can be brewed several times, the strongest bitter beers being brewed five or six times. The first brew is with water, and the second and each subsequent brew is therefore made with an increasingly strong liquor. This prohibition remained in force until about 1553. By 1500 hopped beer had become universal in north-west Europe, the cultivation of hops being especially important in western Germany.

In 1629, European cultivars of Humulus lupulus were introduced to North America, where they then consequently hybridised with native stocks of the same species.

Agriculture

The common cultivated hop is a long-lived woody perennial or herbaceous annual. Hop plants climb hedges or trees in the wild but, in cultivation, they are grown on specially built frames. Like many climbing plants, hops have a preferred mode: they wind clockwise. They produce new vines each year, which die after maturity. They have an extensive root system and grow best on rich alluvial soils or sandy gravely soils that are well drained. In the USA, the plants need irrigation but the UK climate usually provides adequate rain during the growing season.

Distribution of Humulus cultivation is determined by the plant's photoperiodic responses. The daylight hours must be short for flowers to form, with longer daylight hours required for vegetative growth. Plants can still be grown commercially at latitudes unsuitable for natural distribution by the use of artificial lighting. In the wild, the vines grow to 3 m if supported by a tree, and the roots are perennial. However, cultivated vines die back each winter.

If the herbaceous annual vine is grown, the seeds or cones are planted when mature; with perennial varieties, the growth dies back annually. The extensive root system can draw sustenance from a depth of up to 5 m.

Harvesting is done by hand or machine.

Before the First World War, Wye Agricultural College in the south of England identified high resin content the important aim for the breeder. Breeding for this property has taken the typical hop vine a-acid content of 4-5% in 1900 to 12-15% in, for example, the modern cultivar 'Northern Brewer'. This cultivar has been exported to Europe and to the USA, and it is also very resistant to Verticillium dahliae (Verticillium wilt).

The other harmful disease of hops are downy mildews. Its pests include the damson-hop aphid (Phorodon humuli Schrank) and red spider mites (Tetranychus truncates Ehara). Concern over the long-term effects of agrochemicals has led to breeding for pest-resistance. This, and the increased yields of a-acid in the resins and improved mechanisation, have reduced the area needed to cultivate hops and led to the demise of the Cockney hop-picking 'holiday', so characteristic of earlier times in Kent, for example. Dwarf hop plants became available after 1977, and these cultivars lend themselves to the total mechanisation of the crop.

Modern context

'Raw' hops are a sedative, aphrodisiac, restorative tonic for the nervous system, a bitter digestive stimulant and a diuretic. The flowers can be used fresh for insomnia, and fresh hops used in pillows should be changed frequently because, once dry, it becomes a stimulant.

Post-harvest

Freshly picked cones have a high moisture content and need drying in kilns before they can be used for brewing. After drying, they are cured, baled and made ready for market. Boiling the hops in wort, an aqueous infusion of malt, extracts the resins and essential oils that give the delicate hop aroma to beers and aids preservation.

Oast houses were once built as hop kilns, and their characteristic conical shape are an architectural feature of hop-growing districts in the south of England.


From: Seeds of trade (http://www.nhm.ac.uk/seeds)

©  Natural History Museum