|A. oryzae growing on rice to make koji|
(Ahlburg) E. Cohn
Aspergillus oryzae (Chinese: 麴菌, 麴霉菌, 曲霉菌, pinyin: qū meí jūn; Japanese: 麹, kōji, or 麹菌, kōji-kin, Korean: 누룩균, nurukgyun or 누룩곰팡이 nuruk-gompang-i) is a filamentous fungus (a mold). It is used in Chinese, Korean, and Japanese cuisine to ferment soybeans. It is also used to saccharify rice, other grains, and potatoes in the making of alcoholic beverages such as huangjiu, sake, makgeolli and shōchū. The domestication of A. oryzae occurred at least 2000 years ago. A. oryzae is used for the production of rice vinegars.
Dr. Eiji Ichishima of Tohoku University called the kōji fungus a "national fungus" (kokkin) in the journal of the Brewing Society of Japan, because of its importance not only for making the koji for sake brewing, but also for making the koji for miso, soy sauce and a range of other traditional Japanese foods. His proposal was approved at the society's annual meeting in 2006.
"Red kōji-kin" is a separate species, Monascus purpureus.
History of koji
300 BCE – A. oryzae (qu, pronounced "chew") is first mentioned in the Zhouli (Rites of the Zhou dynasty) in China. 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 fermented black soybeans, not to mention grain-based wines (including Japanese sake) and li (the Chinese forerunner of Japanese amazake).
Properties desirable in sake brewing and testing
The following properties of A. oryzae strains are important in rice saccharification for sake brewing:
- 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
Varieties used for shōchū making
- White. Discovered at the beginning of the Taishō period when natural mutation and separation of some black kōji to white was observed. 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, gentle, sweet taste.
- Black. Mainly used in Okinawa to produce Awamori. 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, 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.
- Yellow. 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. 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 and women who previously had no interest in typically strong potato shōchū, playing a rôle in its recent revival.
Initially kept secret, the A. oryzae genome was released by a consortium of Japanese biotechnology companies in late 2005. 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. 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.
Use in biotechnology
A. oryzae is a supporting character (of sorts) in the manga series Moyasimon: Tales of Agriculture and its anime adaptation.
- Index Fungorum
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