Koji

Wikipedia

Aspergillus oryzae, known in English as koji (Japanese: 麹 Hepburn: kōji^?), is a filamentous fungus (a mold) used in Chinese and other East Asian cuisines to ferment soybeans for making soy sauce and fermented bean paste, and also 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 also 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.

The main use of molds has been in the process of making koji (mold-fermented grains and/or soybeans), which serves as a source of more than 50 enzymes in a subsequent fermentation in much the same way that, in the West, the enzymes of malt (steeped and sprouted barley or other cereal grains) are used to make alcoholic beverages.

The nature of koji is embodied in the very characters with which the word is written. In the more traditional form--used with most miso koji and especially with barley koji--the ideographs for "barley:" and "chrysanthemum" are placed side by side. In the more recent form--used especially with ready-made rice koji--the ideographs for "rice" and "flower" are conjoined. The first form is said to have originated in China, whereas the latter was developed in Japan about 1,000 years ago. In both, the notion of grain covered with a bloom of mold is vividly expressed (Shurtleff and Aoyagi 1976; Tamiya 1958).

Since ancient times the koji making process has been unique to East Asia, where it has been used in the preparation of fermented foods such as miso, soy sauce, soy nuggets, sake, shochu (spirits), and rice vinegar ( yonezu ). The only traditional East Asian fermented soyfood not prepared with molds is Japan's natto, and its relatives thua-nao in Thailand and kinema in Nepal; these are bacterial fermentations. Some have suggested that molds are widely used since they grow well in areas having a humid climate and long rainy season during the warm months. In the West mold fermented foods are limited primarily to a number of cheeses characterized by their strong flavors and aromas: Camembert, Blue, Brie, and related types. Because of the widespread use of mold-fermented foods in East Asia, the word "mold" there has a rather positive connotation, something like "yeast" in the West. Most Westerners still have a deep-seated prejudice against moldy products, and they generally associate the word "mold" with food spoilage, as in "moldy bread."

History of koji

300 BCE – A. oryzae 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 douchi, not to mention grain-based wines (including Japanese sake) and li (the Chinese forerunner of Japanese amazake).^[4]

The earliest records of the koji-making process can be traced back to at least 300 BC in China and to the third century AD in Japan. Molds differ in one important respect from yeasts and bacteria in that they can be easily observed with the naked eye (without a microscope) and their growth, form, and color noted. In East Asia it was probably understood that fermentation was a life process long before it was in the West. By the sixth century AD, as recorded in the Ch'i-min yao-shu (the earliest encyclopedia of agriculture), the Chinese had distinct names for two types of molds used in fermented soyfoods; what we now call Aspergillus was then called "yellow robe" and Rhizopus was called "white robe." These cultures were carefully distinguished and propagated from year to year. By the 10th century a koji starter or inoculum was deliberately being used in the preparation of koji for fermented foods (Tamiya 1958; Sakaguchi 1972; 1979).

Properties desirable in sake brewing and testing

These 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

Three varieties of kōji mold are used for making shōchū, each with distinct characteristics.

• White was 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 is 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 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. 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 role in its recent revival.

GENOME

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

Resveratrol can be produced from its glucoside piceid through the process of fermentation by A. oryzae.