anethole

Trans-anethole, C₁₀H₁₂O, is the reason anise, fennel and star anise taste like the same idea despite standing on different branches of the plant kingdom. Anise, Pimpinella anisum, and fennel, Foeniculum vulgare, are both Apiaceae, the carrot and parsley family, and anise's oil alone runs to eighty to ninety-five percent anethole. Star anise, Illicium verum, sits in the unrelated Schisandraceae and still lands on the same molecule, at seventy-two to ninety-two percent of its own oil. Two lineages, separated by an enormous span of evolutionary time, arrived at one aromatic compound and left humans to file the result under a single flavor.

The molecule barely dissolves in water, 0.111 grams per liter, against an easy solubility in ethanol. That gap is the entire mechanism behind the cloud that appears when water hits arak, ouzo or pastis. Diluting the alcohol below what the anethole needs makes it fall out of solution everywhere at once, in droplets that scatter light white rather than separating into an oily layer; chemists named the phenomenon the ouzo effect, after a 2003 paper that gave it that name. The droplets stop growing once they reach about 1.5 micrometers, and the cloud holds for months. The same mechanism needs an alcohol solvent to dilute in the first place, so it never sets up inside a pot of tea, where water is the only solvent from the start.

Chew the seed and the sweetness arrives before the licorice note does, and it comes from the same T1R2/T1R3 receptor that reads sugar: a March 2025 study found anethole activates the human version of that receptor but not the mouse one. How much sweeter than sugar it is has no real answer. The thirteen-times figure that circulates traces to an uncited Wikipedia line, and the ten-times figure in at least one peer-reviewed paper cites a study of rat smooth muscle that never measured taste at all; anethole's solubility, 0.111 grams per liter, is too low for the standard sweetness test to have been run on it in the first place. What is measured is traditional use: Europe's medicines agency recognizes crushed anise seed for mild bloating and gas and as a cough expectorant, one to three and a half grams steeped in 150 milliliters of boiling water, up to three times a day, for no more than two weeks. In this library the same molecule sweetens fifteen recipes, mostly teas, traced to star anise, fennel or anise.