is a component of the hydrocarbon fraction of hop oil. The presence or absence of farnesene (sometimes referred to as beta farnesene) is a distinguishing feature for some hops. In Hallertauer Mittelfrüh and many other (but not all) German varieties; for instance, farnesene is completely absent, while in Czech Saaz, German Tettnanger, all Slovenian varieties, and several American varieties, most notably Sterling, it is present in high levels, at roughly 10% to 20% of total oils. See hallertauer mittelfrueh (hop), tettnanger (hop), saaz (hop), and styrian golding (hop). Farnesene has a woody, herbal, citrus aroma, sometimes described as floral. Because farnesene is hydrophobic and volatile, the compound itself is usually not found in beer unless the beer has been dry hopped with a variety that contains farnesene—and even then it is present in only very small amounts. However, high levels of farnesene in hops generally correlate well with pleasant, noble-type hop aroma in beer. See noble hops.