Humulus lupulus: A major brewing ingredient added to boiling wort to produce bitterness and hop aroma. The plant is a perennial climbing herb which may grow to 6 meters in height with clockwise twisting bines. Male and female plants are found but only the female produce cones. These may be fertilized by pollen from the male plants to produce seeds but this is not favoured in continental production although typical of British hops. Adapted into brewing in the last 1,000 years hops are a fundamental feature of contemporary beers providing bitterness from their a acids and aroma from their hydrocarbon and oxidized oils. Leaf hops are commonly compressed before use but retain the structure of the hop cone while pelleted hops are macerated before compression. Hop oils may be added instead of these and are selective extractions of the bitterness and aroma materials.