Hop

Hop refers to the flowering cones of Humulus lupulus, a perennial climbing plant in the Cannabaceae family. The hop cones contain lupulin glands that harbor bitter acids (alpha and beta acids) and a range of volatile oils. In beer production, hops are used to contribute bitterness, aroma, and stability, and to inhibit unwanted microbial growth.

The plant is dioecious; only female plants produce the cone structures used in brewing. Hops are grown on tall trellises in temperate regions, harvested in late summer, then dried, pelletized, or used fresh. Dried hops are typically stored in cool, dark conditions to preserve alpha acids and aroma compounds.

In brewing, bitterness comes primarily from alpha acids, which isomerize into iso-alpha acids during wort boiling, imparting a counterbalancing bitterness. The essential oils provide aroma notes that vary by variety, ranging from citrusy and piney to spicy or earthy. Hop usage includes bittering addition at the start of the boil, late or dry hopping for aroma, and sometimes multi-hop blends.

Common brewing varieties are differentiated by alpha acid content and aroma profile. Traditional European hops such as Saaz and Hallertau are prized for delicate aroma, while American hops such as Cascade and Citra emphasize citrus and tropical notes. Global production centers include Germany, the Czech Republic, and the Pacific Northwest of the United States.