ABSTRACT
The family Cannabidaceae consists of the two genera Humulus and Cannabis. The hop belongs to the genus Humulus, which comprises three species: H. lupulus (the cultivated or European hop), H. japonicus (the annual Japanese ornamental hop) and H. yunnanensis (a perennial Chinese hop) (Small, 1978). H. lupulus, which has been cultivated for over 1000 years in central Europe (Kohlmann and Kaster, 1976), is a dioecious, windpollinated perennial climbing plant. The commercially important strobiles or ‘cones’ are produced by the female plant and comprise the female inflorescence within enlarged bracts and bracteoles. Lupulin glands, located on the bases of the bracteoles and bracts of the cones, and on the pericarp of fertilized hops, contain a number of resins and essential oils of importance to the brewing industry (Hough et al., 1982). Various essential oils contribute to the flavour and aroma of beer. Resins, of which the a-acids (principally humulone and cohumulone) comprise the most important fraction, impart the characteristic bitterness following their isomerization during the brewing process. The α-acids also act as natural preservatives and foaming agents (Burgess, 1964; Neve, 1991). Male flowers also contain a few resin glands on the locular grooves of the anthers and glands are also present in small numbers on leaves of both sexes, but in insufficient numbers to make their use in the brewing industry a commercially viable proposition.
