The present invention relates to a method of efficiently producing reduced coenzyme Q10 having excellent qualities which is useful as an ingredient in foods, functional nutritive foods, specific health foods, nutritional supplements, nutrients, animal drugs, drinks, feeds, cosmetics, medicines, remedies, preventive drugs, etc. This method is suitable for industrial production thereof.
It is possible to handle reduced coenzyme Q10 in state of being protected from oxidation by molecular oxygen by bringing the reduced coenzyme Q10 in contact with a solvent containing a strong acid. Furthermore, when reduced coenzyme Q10 is crystallized in the presence of a strong acid, crystallization can be carried out while the formation of oxidized coenzyme Q10 as a by product is minimized, and, then high-quality crystals thereof can be produced.