Geosmin

Geosmin ( jee-OZ-min) is a chemical with a distinct earthy or musty odor. It is easily smelled by most people, having a very low odor detection threshold, ranging from 0.006 to 0.01 micrograms per liter in water. Geosmin is responsible for the earthy taste of beetroots and a contributor to the strong scent, known as petrichor, that occurs when rain falls after a spell of dry weather or when soil is disturbed. It is produced by bacteria, especially cyanobacteria, often present in soil and water supplies. Geosmin, along with 2-methylisoborneol, are the major biological causes of muddy odor and flavor in drinking water worldwide and in farmed fish. Geosmin is an irregular sesquiterpenoid. It is a bicyclic alcohol with formula C12H22O, a derivative of decalin. It is produced from the universal sesquiterpene precursor farnesyl pyrophosphate (also known as farnesyl diphosphate), in a two-step Mg2+-dependent reaction. Its name is derived from the Ancient Greek words geō- (γεω-), meaning "earth", and osmḗ (ὀσμή), meaning "smell". The word was coined in 1965 by the American biochemist Nancy N. Gerber (1929–1985) and the French-American biologist Hubert A. Lechevalier (1926–2015).