Publisher Summary The kojic acid, 5-hydroxy-2-(hydroxymethy1)-4H-pyran-4-one is produced from carbohydrate sources in an aerobic process by a variety of microorganisms. Kojic acid was first reported as a crystalline substance from the mycelia of Aspergillus orgzae grown on steamed rice. Kojic acid is a γ-pyrone. The conventional way of numbering the atoms in the γ -pyrone ring of kojic acid is shown. Kojic acid crystallizes in the form of colorless, prismatic needles. Kojic acid is readily soluble in water, ethanol, and acetone; sparingly soluble in ether, ethyl acetate, chloroform, and pyridine; and difficultly soluble in most other liquids. It has been purified by recrystallization from acetone, ethanol-ether, and methanol-ethyl acetate; also, by sublimation under diminished pressure at 150–200°C. In solutions, the quantity of kojic acid has been determined colorimetrically by measuring the intensity of the red color produced with ferrous and ferric chloride, and volumetrically, in the absence of other organic acids, by titration with standard dilute alkali, using Alizarin Orange R37 or phenolphthalein as an indicator.