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Humulus lupulus L.
Cannabinaceae
Common hops
Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.
- Uses
- Folk Medicine
- Chemistry
- Toxicity
- Description
- Germplasm
- Distribution
- Ecology
- Cultivation
- Harvesting
- Yields and Economics
- Energy
- Biotic Factors
- References
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.
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).
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.
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).
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.
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.
Native to Europe and western Asia; now cultivated in North and South America,
Africa, Asia and Australia also. Naturalized in many areas.
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.
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.
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 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.
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.
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.
- Bradford, I. 1979. Hops and hop products. Chemistry and Industry No. 24 (15
Dec.):88–89.
- Buttery, R.G. and Ling, L.C. 1967. Identification of hop varieties by gas
chromatographic analysis of their essential oils. Ag. & Food Chemistry
15(3):531–535.
- C.S.I.R. (Council of Scientific and Industrial Research). 1948–1976. The wealth
of India. 11 vols. New Delhi.
- Duke, J.A. 1972. Isthmian ethnobotanical dictionary. Publ. by the author.
Harrod & Co., Baltimore.
- Duke, J.A. 1978. The quest for tolerant germplasm. p. 1–61. In: ASA Special
Symposium 32, Crop tolerance to suboptimal land conditions. Am. Soc. Agron.
Madison, WI.
- Duke, J.A. 1979. Ecosystematic data on economic plants. Quart. J. Crude Drug
Res. 17(3–4):91–110.
- Duke, J.A. and Wain, K.K. 1981. Medicinal plants of the world. Computer index
with more than 85,000 entries. 3 vols.
- Fernald, M.L., Kinsey, A.C., and Rollins, R.C. 1958. Edible wild plants of
eastern North America. Rev. Ed. Harper & Bros., New York.
- Grieve, M. 1931. A modern herbal. Reprint 1974. Hafner Press, New York.
- Hartwell, J.L. 1967–1971. Plants used against cancer. A survey. Lloydia 30–34.
- Leung, A.Y. 1980. Encyclopedia of common natural ingredients used in food,
drugs, and cosmetics. John Wiley & Sons. New York.
- Moerman, D.E. 1982. Geraniums for the Iroquois. A field guide to American
Indian medicinal plants. Reference Publications, Algonac, MI.
- Sutcliffe, H.M., Ernst, A.J., and Aronovsky, S.I. 1950. Hop vines for paper. The
Hopper Jan.
Complete list of references for Duke, Handbook of Energy Crops
Last update Wednesday, January 7, 1998 by aw