Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Nootkatone is a natural organic compound and is the most important and expensive aromatic of grapefruit. It is a sesquiterpene and a ketone. Nootkatone was previously thought to be one of the main chemical components of the smell and flavour of grapefruits. In its solid form it is usually found as crystals. As a liquid, it is viscous and yellow. Nootkatone is typically extracted from grapefruit, but can also be manufactured with genetically modified organisms, or through the chemical or biochemical oxidation of valencene.