Humulus lupulus
Humulus lupulus, commonly known as hops or common hop, is a dioecious, rhizomatous, twining perennial vine in the Cannabaceae family, native to temperate regions of Eurasia and widely naturalized in North America.[1][2] The plant features rough, green stems that can reach heights of 15 to 25 feet, opposite leaves that are 3- to 5-lobed with toothed margins, and yellow-green flowers: male in loose catkins and female forming cone-like strobiles that contain resinous lupulin glands.[1][3] It thrives in moist, rich, well-drained soils in full sun to partial shade, often along streambanks, woodlands, and disturbed areas, and dies back in winter before regrowing from roots in spring.[2][3] Primarily cultivated for its female cones, harvested in late summer to early autumn, H. lupulus plays a central role in the global beer brewing industry, where the α-acids (humulones) and essential oils in the lupulin provide bitterness, aroma, and antimicrobial properties to balance malt sweetness and preserve the beverage.[4] Varieties are selected for seedless cones to optimize yield and quality, with major production in regions like Europe, the United States, and New Zealand under temperate climates between 35° and 55° N latitude.[4] Beyond brewing, the plant has ornamental value in gardens for covering arbors and trellises, attracting pollinators like butterflies, and historical uses in traditional medicine for sedative and anti-inflammatory effects due to compounds like xanthohumol.[1][4]Description
Morphology and growth
Humulus lupulus is a perennial herbaceous climbing plant in the family Cannabaceae, characterized by its vigorous growth as a vine that can reach heights of 6 to 10 meters in a single season. It produces annual bines that emerge from an underground rhizomatous rootstock, which allows the plant to overwinter and regrow each spring. The stems, known as bines, are robust and twine clockwise around supports using hooked trichomes rather than tendrils, enabling rapid vertical growth of over 30 cm per day under optimal conditions. These bines are typically green, pubescent at the nodes with glandular hairs, and lack wings, measuring 100–700 cm in length.[5][6][7] The leaves of H. lupulus are opposite or alternate, simple, and palmately lobed, usually with three to five (occasionally up to seven) deep lobes that give them a maple-like appearance. Leaf blades are cordate at the base, measure 3–15 cm in length and width, and feature serrated margins; they are green with glandular dots on the surfaces and petioles up to 7 cm long. Adaxial surfaces may be sparsely pubescent, while abaxial ones are more densely so, with over 20 hairs per cm on the midrib and numerous glands between veins. Morphological variations occur across subspecies: European types (H. lupulus ssp. lupulus) have shallower lobes and less pubescence, whereas North American wild hops (ssp. lupuloides or neomexicanus) exhibit deeper lobes, more pronounced pubescence, and sometimes elongated or striped leaves.[6][8][5][9] Root systems consist of a perennial rhizome that spreads horizontally underground, producing adventitious roots and new shoots; the crowns can remain productive for many years but are typically pruned annually in cultivation to manage vigor. Lateral branches arise from nodes along the bines, bearing the reproductive structures. The plant is dioecious, with male and female flowers on separate individuals; females are generally taller and produce longer laterals with more nodes than males, particularly in the second year of growth, reflecting sexual dimorphism in height (females up to 4.8 m vs. males 4.2 m at maturity) and shoot density. Male flowers form loose panicles, while female flowers develop into papery, resinous cones (strobili) 1–10 cm long, containing lupulin glands essential for their commercial use. Fruits are small, ovoid achenes enclosed within the cones.[7][10][5][6] Growth is seasonal and photoperiod-sensitive, initiating in early spring with shoot emergence after cold stratification for rhizomes or seeds. Bines elongate rapidly during long summer days (requiring 14–16 hours of light) but flower in response to shortening days (<15 hours), with cone maturation occurring 30–50 days later in late summer. The plant dies back to the rhizome in autumn, entering dormancy during winter; full vigor is achieved in the second year post-planting, with commercial fields trained on trellises to support the weight and facilitate harvest. In wild settings, it thrives in moist, temperate environments between 30° and 50° latitude, climbing shrubs or trees for support.[7][9][5][6]Chemical composition
_Humulus lupulus, commonly known as hops, contains a diverse array of bioactive compounds primarily concentrated in the lupulin glands of the female cones. The chemical composition varies by cultivar, environmental factors, and plant part, but key constituents include bitter acids, essential oils, polyphenols, and other secondary metabolites. These compounds contribute to the plant's role in brewing, medicine, and pharmacology, with bitter acids and oils being most abundant in mature cones.[11] Bitter acids, or humulones and lupulones, are prenylated phloroglucinol derivatives that constitute 2-17% of the dry cone weight, with higher concentrations (up to 30%) in the lupulin glands. The α-acids, including humulone (35-50% of total α-acids), cohumulone (20-35%), and adhumulone (10-20%), isomerize during brewing to form iso-α-acids responsible for beer bitterness and foam stability. β-Acids, such as lupulone (30-50% of total β-acids), exhibit antimicrobial properties but are less soluble in beer. These acids' content is genetically determined, with commercial varieties selected for α-acid levels of 8-15%.[12][11] Essential oils, comprising 0.5-3% of dry cone mass, are terpenoid mixtures that impart aroma to beer and potential therapeutic effects. Monoterpenes like myrcene (8-52% of oil) dominate in varieties such as Cascade and Northern Brewer, contributing herbal and citrus notes, while sesquiterpenes including α-humulene (12-51%) and β-caryophyllene (4-11%) prevail in noble hops like Saaz and Hallertauer, providing earthy and spicy profiles. Oxygenated compounds, such as linalool (0.2-3.2%), add floral aromas. Oil composition influences hop variety classification for brewing.[12][13] Polyphenols, ranging from 3-14% of dry cones, include flavonoids and phenolic acids with antioxidant and estrogenic activities. Prenylated chalcones like xanthohumol (0.1-1% of cones) and its metabolites, such as isoxanthohumol, show anticancer potential, while flavanols like catechin (0.03-0.3%) and glycosides like rutin contribute to oxidative stability. 8-Prenylnaringenin, a potent phytoestrogen, occurs at 25-60 mg/kg in cones. These compounds are more abundant in leaves and early-stage cones.[12][11] Other constituents include carbohydrates (up to 15% as pectins and sugars), proteins (10-15%), and minor volatiles like aldehydes and esters in aqueous extracts, which vary by cultivar and support the plant's nutritional profile.[12]| Compound Class | Key Examples | Typical Content (% dry cone weight) | Primary Function |
|---|---|---|---|
| Bitter Acids | Humulone, Lupulone | 2-17% | Bitterness, Antimicrobial |
| Essential Oils | Myrcene, α-Humulene | 0.5-3% | Aroma, Sedative |
| Polyphenols | Xanthohumol, Quercetin | 3-14% | Antioxidant, Phytoestrogenic |