Humulene is a component of the hydrocarbon fraction of hop oil. It is found with other essential oils in the lupulin gland, where it is formed in the final stages of hop cone maturation. As the hop cone ripens, trace amounts of oxygenated compounds of the essential oil appear first. Caryophyllene and humulene follow next, and finally, myrcene. The ratio of humulene to caryophyllene varies from one hop variety to another, but many brewers consider a good aroma to be one that has a ratio of greater than 3:1. Such hops tend to be floral, herbal, and spicy in character. Some varieties, such as Hallertauer Mittelfrüh and U.K. Kent Golding, may contain 30% or more of their essential oils in humulene, but, because humulene is highly volatile and hydrophobic, only trace quantities of it may actually reach the final beer. Oxidation products of humulene, on the other hand, especially humulene mono- and di-epoxides, can impart significant amounts of aroma to beer. Humulene epoxide III is one of the most potent flavor compounds in Hallertauer Mittelfrüh, for instance, a variety that is high in humulene but relatively low in total oils. Allowing hops that are high in humulene to age in bales for several weeks prior to pelletizing will result in greater amounts of humulene epoxides, as well as other hop oil oxidation products, which some brewers believe can significantly increase the hops’s aroma potential.