Anethole is an aromatic compound that accounts for the distinctive "licorice" flavor of anise, fennel, star anise, and anise myrtle. It has a chemical formula of C10H12O, and is closely related to
estragole, or p-allylanisole or methyl chavicol, which is a natural organic compound.
Estragole is a double-bond isomer of anethole. It is a colorless to pale yellow liquid. It is the primary constituent of tarragon oil making up 60-75% of the oil. It is also found in basil (23-88%), pine oil, turpentine and Syzygium anisatum. Remember - when your food smells like "licorice" it contains one or more of these four ingredients: fennel, anise, tarragon, basil. That's why fennel is like a big licorice-smelling onion! Never (ever) be without fennel. Experiment with it in place of onion, and chop the tiny fronds (which look like dill) for an aromatic garnish (sprinkle on top of your finished dish), and don't chop the fronds until seconds before you serve. Yes, there are three main types of fennel, but that's another post...