Geosmin (trans-1,10-dimethyl-trans-9-decalol), a well-known, highly odorous compound, has recently been identified and quantified in red and sweet white wines, as well as in grape juice before alcoholic fermentation. Geosmin is a chiral compound and the (–) form is much more odoriferous than the (+) form. Enantioselective multidimensional gas chromatography analysis of a purified Cabernet Sauvignon wine extract revealed the presence of only one enantiomer: (–) geosmin. In grape juices obtained from rotten grapes and in wines this compound can be found at concentrations much higher than its olfactory perception threshold, indicating that it contributes to their earthy aroma. (–) Geosmin is also the only enantiomer to have been identified in pure cultures of Streptomyces sp. and Penicillium sp. strains isolated from rotten grapes.