Hop

Hop, common name for any of a genus of vines (see Nettle). Hop plants have rough stems and heart-shaped leaves of three to seven lobes. Small staminate and pistillate flowers are produced on separate plants. Staminate flowers are borne in loose panicles, and pistillate flowers, borne in catkins, develop into achenes—dry, one-seeded fruits that are borne at the bases of overlapping bracts. The entire conelike catkin of achenes and bracts, the hop of commerce, is covered with a fine yellow powder called lupulin or hop flour. Lupulin, which gives the hop its bitter flavor and aroma, is used as a sedative. The common hop is native to Eurasia and is naturalized in the northern and western United States, Australia, and Brazil. The American hop is native to temperate North America. Several unrelated plants are commonly called hop, including bryony and black medick. The so-called hop plant is sweet marjoram.

Catkins of common and American hop are extensively cultivated as a source of hops used in brewing. Common hop is cultivated throughout suitably warm areas of Europe, North America, Australia, and New Zealand. Germany, England, and the United States are leading hop producers. Cultivation of American hop is common only in the Pacific states. Annual hop production in the United States is about 22,679,600 kg (about 50 million lb).

Hop must be grown in areas having an abundant rainfall during the growth period and abundant sunlight during the fruiting period. It is usually grown from cuttings that are planted in rows about 2 m (about 6 ft) apart in late winter or early spring. Only female plants produce fruit, but a few male plants are included in each hop field because fertilized catkins grow larger and more rapidly than unfertilized catkins. Hop plants are trained to, or guided by, strings suspended above the rows. Catkins become aromatic in late summer and are then harvested.

Scientific classification: Hop plants constitute the genus Humulus, of the family Moraceae. The common hop is classified as Humulus lupulus, the American hop as humulus lupulus variety lupuloides.