Aspergillus oryzae

The following properties of A. oryzae strains are important in rice saccharification for sake brewing:[7]

• Growth: rapid mycelial growth on and into the rice kernels
• Enzymes: strong secretion of amylases (α-amylase and glucoamylase); some carboxypeptidase; low tyrosinase
• Aesthetics: pleasant fragrance; accumulation of flavoring compounds
• Color: low production of deferriferrichrome (a siderophore), flavins, and other colored substances

Three varieties of kōji mold are used for making shōchū, each with distinct characteristics.[8][9][10]

Genichirō Kawachi (1883 -1948), who is said to be the father of modern shōchu and Tamaki Inui (1873 -1946), a lecturer at University of Tokyo succeeded in the first isolating and culturing aspergillus such as A. kawachii, A. awamori and a variety of subtaxa of A. oryzae, which made great progress in producing shochu in Japan, and since then aspergillus developed by Kawachi has also been used for soju and makgeolli in Korea.[11][12][13]

• Yellow kōji (A. oryzae etc) is used to produce sake, and at one time all honkaku shōchū. However, yellow kōji is extremely sensitive to temperature; its moromi can easily sour during fermentation. This makes it difficult to use in warmer regions such as Kyūshū, and gradually black and white kōji became more common in production of shōchū. Its strength is that it gives rise to a rich, fruity, refreshing taste, so despite the difficulties and great skill required, it is still used by some manufacturers. It is popular amongst young people who previously had no interest in typically strong potato shōchū, playing a role in its recent revival. Thus, white and black kōji are mainly used in the production of shōchū, but only yellow kōji (A. oryzae) is usually used in the production of sake.
• White kōji (A. kawachii etc) was discovered as a mutation from black kōji by Genichirō Kawachi in 1923.[11] This effect was researched and white kōji was successfully grown independently. White kōji is easy to cultivate and its enzymes promote rapid saccharization; as a result, it is used to produce most shōchū today. It gives rise to a drink with a refreshing, mild, sweet taste.
• Black kōji (A. awamori also known as A. luchuensis etc) is mainly used to produce shōchū and awamori. In 1901, Tamaki Inui, lecturer at University of Tokyo succeeded in the first isolating and culturing. In 1910, Genichirō Kawachi succeeded for the first time in culturing var. kawachi, a variety of subtaxa of A. awamori. This improved the efficiency of shochu production.[11] It produces plenty of citric acid which helps to prevent the souring of the moromi. Of all three kōji, it most effectively extracts the taste and character of the base ingredients, giving its shōchū a rich aroma with a slightly sweet, mellow taste. Its spores disperse easily, covering production facilities and workers' clothes in a layer of black. Such issues led to it falling out of favour, but due to the development of new kuro-kōji (NK-kōji) in the mid-1980s,[14] interest in black kōji resurged amongst honkaku shōchū makers because of the depth and quality of the taste it produced. Several popular brands now explicitly state they use black kōji on their labels.

Initially kept secret, the A. oryzae genome was released by a consortium of Japanese biotechnology companies[15] in late 2005.[16] The eight chromosomes together comprise 37 million base pairs and 12 thousand predicted genes. The genome of A. oryzae is thus one-third larger than that of two related Aspergillus species, the genetics model organism A. nidulans and the potentially dangerous A. fumigatus.[17] Many of the extra genes present in A. oryzae are predicted to be involved in secondary metabolism. The sequenced strain isolated in 1950 is called RIB40 or ATCC 42149; its morphology, growth, and enzyme production are typical of strains used for sake brewing.[18]

Trans-resveratrol can be efficiently cleaved from its glucoside piceid through the process of fermentation by A. oryzae.[19]

麹 (chinese qu, japanese Kōji) which means mold used in fermented foods, was first mentioned in the Zhouli (Rites of the Zhou dynasty) in China in 300 BCE. Its development is a milestone in Chinese food technology, for it provides the conceptual framework for three major fermented soy foods: soy sauce, jiang / miso, and douchi, not to mention grain-based wines (including Japanese sake and Chinese huangjiu) and li (the Chinese forerunner of Japanese amazake).[20][18]

• 
  Conidiophores with conidia of the microscopic fungus A. oryzae under light microscope
• 
  Four Aspergillus colonies grown at 37°C for three days on rich media: The bottom two are A. oryzae strains.

• Making Rice Koji from Koji Spores
• Sake World's description of koji
• Aspergillus oryzae genome from the Database of Genomes Analysed at NITE (DOGAN)