The hop plant, Humulus lupulus, is a vigorous, perennial member of the Cannabaceae family, which also includes hemp. It is primarily cultivated for its female flowers, used in brewing to provide bitterness, flavor, and aroma.
Overall Growth Habit and Classification
The hop plant is a herbaceous perennial, meaning it dies back to the ground each winter and regrows from a cold-hardy root crown, or rhizome, in the spring. This growth habit allows it to return for many years, often remaining productive for 10 to 20 years or more. The plant is dioecious, a term indicating that male and female flowers are borne on separate plants.
The stems that emerge annually are correctly termed “bines,” not vines, which is a distinction based on how the plant climbs. True vines, like grapes, use specialized structures such as tendrils or suckers to grip supports. The hop uses its own stem, which wraps itself around a support structure in a corkscrew pattern, typically twining in a clockwise direction. This vigorous growth allows the bine to climb rapidly, often reaching impressive heights of 20 to 25 feet in a single growing season when supported by a trellis.
Distinctive Features of Leaves and Bines
The bines possess a rough texture due to the presence of stiff, backward-pointing hairs, or trichomes, which are instrumental in providing the grip necessary for vertical ascent. These hairs make the stem feel slightly abrasive to the touch. The bines are generally green when young, becoming tougher as they mature throughout the season.
The foliage of the hop plant is characterized by large, deep green leaves that are arranged oppositely along the bine. The leaves are palmate, or hand-shaped, typically featuring three to five distinct lobes, although some can have up to seven. The edges of the leaves are distinctly serrated, and the surface has a rough, somewhat sandpaper-like texture due to small hairs covering the leaf tissue. The leaves are substantial, often ranging from 3 to 5 inches in width, creating a dense canopy of vegetation.
Appearance and Structure of the Hop Cones
The most recognized part of the plant is the female flower, commonly known as the hop cone, or technically, the strobile. These cones, which develop from late July into August, are papery, ovoid structures that resemble small, pale green to yellow-green pine cones. They are harvested when they are approximately 1 to 2 inches long, though size varies significantly by variety.
The cone is constructed of numerous overlapping, leaf-like scales called bracts and bracteoles, which are attached to a central stem known as the strig or rachis. This structure protects the small, bright yellow lupulin glands found at the base of the bracteoles. These glands are the source of the plant’s value, containing the resins, such as alpha acids, and essential oils that impart bitterness and aroma to beer. When fresh, these glands are visible as a yellowish powder that is sticky and carries a potent, resinous scent.