Anethole
The sweet, licorice-like compound of anise, fennel and star anise, much sweeter than sugar to the nose.
Also: anise compound, licorice aroma, trans-anethole
Anethole is an aromatic compound that provides the licorice flavour of anise, star anise and fennel, and it is far sweeter than sucrose. It dissolves in alcohol but turns cloudy when water is added, the louche effect seen in ouzo, pastis, sambuca and arak. Unrelated plants share it, which is why star anise from China and anise seed from the Mediterranean taste alike. In cooking anethole mellows with heat and works with fat, so it flavours pho broth, braised meat and sausage. In India, saunf is chewed after meals, and in Italy fennel seed flavours pork. Use small quantities, as it dominates.