Koji is produced by introducing the mould "Aspergillus oryzae" onto steamed white rice. This mould culture comes from dried "A. oryzae" spores called "tane-koji" or "starter koji" and is isolated from plant matter (usually rice) and cultivated. In the past, the natural presence of "A. oryzae" spores was relied upon to create koji, but because of the difficulty of producing the culture, tane-koji is added almost exclusively in both industrial and traditional production of miso. Tane-koji is produced much in the same way as koji, but also has a small portion of wood ash added to the mixture which gives important nutrients to the fungus as well as promoting sporulation.