The present invention concerns a method of producing and enantiomerically pure alpha-ionone. Further, the invention concerns a nucleic acid that comprises a sequence that encodes a lycopene-epsilon-cyclase (EC), a lycopene-epsilon-cyclase (EC), plasmids, which encode components of the alpha-ionone biosynthesis and a microorganism that contains heterologous nucleotide sequences which encode the enzymes geranylgeranyl-diphosphate-synthase, isopentenyl-diphosphate-isomerase (IPI), phytoene desaturase-dehydrogenase (crtI), phytoene synthase (crtB), lycopene-epsilon-cyclase (EC) and carotenoid-cleavage-dioxygenase (CCD1). Further, the invention concerns a method of producing highly pure epsilon-carotene.