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Humulus lupulus L.

Cannabinaceae
Common hops

Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.


  1. Uses
  2. Folk Medicine
  3. Chemistry
  4. Toxicity
  5. Description
  6. Germplasm
  7. Distribution
  8. Ecology
  9. Cultivation
  10. Harvesting
  11. Yields and Economics
  12. Energy
  13. Biotic Factors
  14. References

Uses

In 1976, ca 100,000,000 kg of hops were grown, solely for the brewing industry (Bradford, 1979). Bitter substance obtained from glandular hairs of strobilus used by brewers for giving aroma and flavor to beer. Originally used for their preservative value, the hops were only later noted to impart a flavor to beer. There is one german patent for adding hops to sausages as a "natural" preservative. Substance prevents gram-negative bacteria from growing in the beer or wort. Amount of essential oil varies from 0.2–0.5%. Oil of Hops also used in perfumes, cereal beverages, mineral waters, and tobacco. Stems are source of fiber like soybean stalks, cotton stalks, flax shives and similar agricultural residues and have, been suggested for pulp or biomass production. Fiber has relatively high lignin and low pentosan content, with a cellulose content lower than any of them. Sometimes used for filler material in corrugated paper or board products, but unsuited for corrugated paper because of low pulp yield and high chemical requirement or for production of high-grade pulp for speciality paper. Young bleached tops used as a vegetable, especially in Belgium. Romans ate the young shoots like asparagus. Chopped very fine and dressed with butter or cream "the young shoots are excellent" (Fernald et al., 1958). Alcoholic extracts of hops in various dosage forms have been used clinically in treating numerous forms of leprosy, pulmonary tuberculosis, and acute bacterial dysentery, with varying degrees of success in China. Hops extracts are said to have various biological activities (antimicrobial activities due to the bitter acids, especially lupulone and humulone), strong spasmolytic effects on isolated smooth muscle preparations; hypnotic and sedative effects (disputed by one report); estrogenic properties were not observed in a more recent study; and allergenic activity on humans, causing contact dermatitis due to the pollen. Extracts are used in skin creams and lotions, in Europe, for alleged skin-softening properties. Extracts and oil are used as flavoring in nonalcoholic beverages, frozen dairy desserts, candy, baked goods, gelatins, and puddings, with the highest average maximum use level of 0.072% reported for an extract used in baked goods (Leung, 1980). According to Grieve, hops steeped in sherry make an excellent stomachic cordial. Leaves and flower heads have been used to produce a fine brown dye (Grieve, 1931). Recently, counterculture entrepreneurs have apparently succeeded in grafting hops tops on marihuana bottoms and getting a "heady hop". Conversely, they might have succeeded in getting a perennial marihuana by grafting the annual herb onto the perennial hop.

Folk Medicine

Dried strobili used medicinally as a bitter tonic, sedative, hypnotic. The decoction from the flower is said to remedy swellings and hardness of the uterus. A cataplasm of the leaf is said to remedy cold tumors. The dried fruit, used for poultices and formentations, is said to remedy painful tumors. The pomade, made from the lupulin, is said to remedy cancerous ulcerations (Hartwell, 1967–1971). Reported to be anaphrodisiac, anodyne, antiseptic, diuretic, hypnotic, nervine, sedative, soporific, stomachic, sudorific, tonic, and vermifuge, hops is a folk remedy for boils, bruises, calculus, cancer, cramps, cough, cystitis, debility, delirium, diarrhea, dyspepsia, fever, fits, hysteria, inflammation, insomnia, jaundice, nerves, neuralgia, rheumatism, and worms (Duke and Wain, 1981). Moerman (1982) gives interesting insight on Amerindian uses of a plant alien to them originally. Delaware Indians heated a small bag of leaves to apply to earache or toothache. More interesting was the Delaware use of hops as a sedative, drinking hop tea several times a day to alleviate nervousness. Cherokee, Mohegan, and Fox also used the plant as a sedative. George III is said to have slept on a pillow stuffed with hops to alleviate some symptoms of his porphyria. I would personally not hesitate to drink a chamomile-hop-valerian tea as a sedative or herbal sleeping potion, but I would never recommend it to anyone else. The antibiotic principle lupulone is tuberculostatic (Duke, 1972).

Chemistry

According to the Wealth of India (C.S.I.R., 1948–1976), hops contain 6–12% moisture, 11–21% resins (no tetrahydrocannabinols), 0.2–0.5% volatile oils, 2–4% tannins, 13–24% protein, 3–4% fructose and glucose, 12–14% pectins, and 7–10% ash. According to Leung (1980) hops contain 0.3 to 1% volatile oil; 3 to 12% resinous bitter principles composed of a-bitter acids (humulone, cohumulone, adhumulone, prehumulone, posthumulone, etc., and b-bitter acids (lupulone, colupulone, adlupulone, etc., in decreasing concentration); other resins, some of which are oxidation products of the a- and b-acids; xanthohumol (a chalcone); flavonoid glycosides (astragalin, quercitrin, isoquercitrin, rutin, kaempferol-3-rutinoside, etc.); phenolic acids; tannins; lipids; amino acids; estrogenic substances; and many others. The volatile oil is made up mostly of humulene (a-caryophyllene), myrcene, b-caryophyllene, and farnesene, which together may account for over 90% of the oil. Other compounds number over 100, including germacratriene, a- and b-selinenes, selina-3,7(11)-diene, selina-4(14),7(11)-diene, a-copaene, a- and b-pinenes, limonene, p-cymene, linalool, nerol, geraniol, nerolidol, citral, methylnonyl ketone, other oxygenated compounds, 2,3,4-trithiapentane (present only in oil of unsulfured hops in ca 0.01%), S-methylthio-2-methylbutanoate, S-methylthio-4-methylpentanoate, and 4,5-epithiocaryophyllene (Leung, 1980). Buttery and Ling (1967) compare 5 cvs for 76 of their volatile oil components. Countering claims that the "wonder cure" GLA (gamma-linolenic acid) is found only in mother's milk and evening prim-rose, I consulted the USDA lab at Peoria, and learned that GLA was also in hops and borage, to mention just a few of the other vegetable sources.

Toxicity

Hops dermatitis has long been recognized. Not only hands and face, but legs have suffered purpuric eruptions due to hop picking. Although only 1 in 3,000 workers is estimated to be treated, one in 30 are believed to suffer dermatitis (Mitchell and Rook, 1979).

Description

Perennial herbaceous vine, living 10–20 years, with horizontal and vertical roots, the horizontal roots spreading out at depth of 20–30 cm and giving rise to fibrous roots in upper layers of soil, the vertical roots developing downward to depth of 152 cm with spread of 183–244 cm with no fibrous roots; stems annual, slender, climbing, up to 9 m in length, often with stout hooked hairs; leaves opposite, cordate, 3- to 5-lobed, margins serrate, petioles slightly fleshy with stout hooked hairs; plants dioecious with unisexual flowers on separate plants, but occasionally monoecious plants occur, in which case male or female flowers are often infertile; wind-pollinated; female inflorescence cone-like, 2.5–5 cm long; male flowers in long racemes.

Germplasm

Reported from the Eurosiberian Center of Diversity, hops, or cvs thereof, is reported to tolerate bacteria, disease, frost, fungi, high pH, insects, low pH, mildew, mycobacteria, viruses, and wilt (Duke, 1978). Many varieties are available. Morphological studies indicate that Japanese, European and American plants may be characterized by their hairy behavior at node part of stem. Varieties may also be classified into early, midseason, and late. Some triploid varieties grown in Europe are seedless. Resin content is controlled by many pairs of genes. Disease resistance is found in some tetraploids. Most countries both export and import hops for a variety of beer flavors. Cultivars vary also as to harvest time, susceptibility to downy mildew, characters of vine (lobes of leaf, number of nodes, color of young shoot (red, violet or pale green), thickness of stem;, and characters of cone (size, weight, number of bracts, total resin and yield per ha). Some of the better known cultivars being grown in the world today include the following: Italian Wild Type: Saaz, Early Green Dauba, Hallertau, Early Zug, Spalt, Fuggle, Sapporo No. 5 and 6; American Wild Type: Cat's Tail, Early Cluster, Riverside Seeling, Humphries, Kaitakushi, Shinshuwase; Japanese Wild Type: Sonoma; Canadian Wild Type: Canadian, English Cluster, American, American No. 2, B.C. Golding. In Japan about 96% of the hops crop is grown from the variety Shinshuwase.

Distribution

Native to Europe and western Asia; now cultivated in North and South America, Africa, Asia and Australia also. Naturalized in many areas.

Ecology

Ranging from Boreal Wet through Subtropical Dry Forest Life Zones, hops is reported to tolerate annual precipitation of 3.1 to 13.7 dm (mean of 34 cases = 7.4), annual temperature of 5.6 to 21.3°C (mean of 34 cases = 10.0), and pH of 4.5 to 8.2 (mean of 26 cases = 6.5) (Duke, 1978,1979). Suitable for temperate climates between latitudes 35–51°N and 34–43°S, with mean summer temperatures of 16–18°C. Hops are quite hardy if other growing conditions are good. When dormant, they withstand freezing; however, a severe frost will kill young, tender vines in spring. Annual rainfall requirement is about 30 cm, distributed between March and August. Dry weather in September is best for the harvest. Hops do well over a wide range of soils provided they are fertile and moisture-holding. Light to heavy loams are best. Soil depth of 45 dm is required for the Goldings varieties.

Cultivation

Plants propagated from seed which require dormancy period for germination. More frequently propagation from layering or cuttings from established stocks each place. Plant to about 2 m x 2 m, for ca 2600 plants/ha. When growing commences early in spring, reduce shoots to 4–12. Various types of pole training are used. Fertilization requirement depends on soil type and variety of hop planted. Green manure often sown in August and plowed under to provide organic matter. Vegetative and reproductive growth of hops three years or older seem to be improved by pruning. Irrigation may be practiced. Hop cultivations in Japan and elsewhere are usually conducted by contract system between beer company and grower. In Japan, new shoots arise in April; flowers open late in June; cones begin to develop early in July; harvest begins at beginning of August.

Harvesting

Hops are usually picked by hand. However, more recently, picking machines weighing about 160 kg are able to pick 8–10 kg/hr in 5–7 days, 500–700 kg of cones can be picked from 10–14 ha. Hops collected in September when they are ripe, carefully dried by artificial heat and packed in bags or bales. From bloom to harvest requires about 40 days. Sometimes hops are treated with sulfur dioxide to improve the color and prevent change of active principle. Hops deteriorate upon aging and exposure to atmosphere. Drying is an important process as moisture content must be reduced from 80% to 6%. Kiln-drying is practiced in some humid areas.

Yields and Economics

Yields vary according to locality, climatic conditions, and variety. Average yields range from 860 to 1890 kg cones/ha. Best yielders are: English Cluster, 1763 kg/ha); Shinshuwase (1664 kg/ha); American (1580 kg/ha); and American No. 2 (1546 kg/ha). Under ideal conditions up to 4,000 kg cones/ha have been produced. Principal hop-producing regions are: United States (Northwest and New York), England, Czechoslvakia, Germany, Yugoslavia, France, Belgium, Poland, USSR and Canada. Hops are grown in mnay other countries also. In 1971, United States production was 23.3 million kg, averaging about $1.40/kg. United States imports about 6 million kg, mostly from Europe for different flavors. A growing amount is being marketed in extract form. Japan produces about 941,000 kg annually.

Energy

Having no measured total biomass data, I am quick to estimate that well over 10 MT/ha of dry aerial biomass is produced per year by the weedy species in the alluvial reaches of the Potomac, where its relative Cannabis probably produces a significant amount of biomass locally. I suspect that the cv would give as much total biomass renewably if harvested annually. Yield of dry vines varies from ca 1–4 MT/ha (about equalling cone yields), with about 30% of vine left in field as stubble. About 18,000 tons of dry vine were produced per year in the United States (Sutcliffe et al., 1950) which could be used for pulp or biomass. Hop vines have 26.2% lignin as compared to 16.8% in wheat straw; cellulose 42.4% as compared to 54.7% in wheat. The stubble as well as the hop residues, after processing, could, of course, be channelled into energy production. Conventionally, the spent hops are often used as fodder or manure.

Biotic Factors

Many fungi cause diseases in hop plants: Armillaria mellea, Ascochyta humuli, Cercospora cannabis, C. humuli, Erysiphe cichoracearum, Fumago vagans, Fusarium oxysporum, F. sambucinum, F. solani, Gibberella pulicaria, Glomerella cingulata, Leptosphaeria doliolu, Mycosphaerella erysiphina, Oidium erysiphoides, Peronoplasmopara humuli, Phyllosticta decidua, Ph. humuli, Cylindrosporium humuli, Phytophthora cactorum, Podosphaera humuli, Pseudoperonospora humuli (Downy mildew), Rhizoctonia solani, Sclerotinia libertiana, S. sclerotiorum, Septoria humuli, S. lupulina, Sphaerotheca humuli, S. macularis, Typhula humulina, Ureolella tami var. humuli, Verticillium albo-atrum, V. dahliae, V. tricorpus, Botrytis cinerea (Gray mold). Following bacteria also attack hops: Agrobacterium tumefaciens, Corynebacterium humuli and Pseudomonas cannabina. Cuscuta europaea also parasitizes the plant. Viruses known to attack hops include: Chlorotic disease, Chloritic mosaic, Fluffy tip, Mosaic, Nettlehead-Humulus virus 2, and Split-leaf blotch. Nematodes isolated from hops include: Ditylenchus destructor, Heterodera humuli, Meloidogyne hapla, M. incognita, and M. javanica, (Golden, p.c. 1984). Injury by aphids and spider mites (Tetranychus) may be serious.

References

Complete list of references for Duke, Handbook of Energy Crops
Last update Wednesday, January 7, 1998 by aw