A varietal identification procedure for hop cones and pellets is described, in which the composition of the bitter substances (determined by HPLC), especially the percentage of cohumulone in the total alpha acid content, and that of the essential oil (determined by gas chromatography) are compared with a database of varietal composition profiles derived from the analysis of statistically representative samples. The most useful oil constituents for this purpose are farnesene, the selenenes, 2-methylbutyl isobutyrate, humulene, 2-nonanol and the eudesmols. It is pointed out that some older varieties (especially European aroma hops) are not genetically homogeneous, and therefore exhibit considerable variation in composition. Subpopulations derived from individual plants of these varieties (such as virus free propagated stock, or populations grown outside the variety's country of origin) are much more uniform in composition (being genetically identical) but may not be typical of the variety as a whole. For instance, American Tettnang hops contain only traces of 2-nonanol, whereas the ancestral Tettnanger from Germany normally contains this substance at concentrations similar to those in other European aroma varieties. While many varieties can be uniquely identified by their composition profiles, there are groups of varieties in which the members cannot be reliably distinguished from one another by this method. Mixtures of hop varieties can also be detected and the constituents identified, not only in consignments of whole hops (by analysing individual cones) but sometimes also in powders and pellets, where minor deviations from the profile of the declared variety in one or two particulars are likely to result from adulteration with another variety.
Keywords : analysis bitter substances composition essential oil hop pellet hops identification variety