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Jiuqu (simplified Chinese: 酒曲; traditional Chinese: 酒麴; pinyin: Jiǔ qū) is a type of East Asian dried fermentation starter grown on a solid medium and used in the production of traditional Chinese alcoholic beverages. The Chinese character 麴 is romanised as qu in pinyin, chhu or chu in other transcription systems. The literal translation of jiuqu is "liquor ferment", although "liquor mold" or "liquor starter" are adequate descriptions.

Jiuqu specifically refers to a type of ferment (Qu 麴) used to manufacture alcoholic products (Jiu 酒), such as Huangjiu (Cereal Wines), Baijiu (Distilled Spirits) and Jiuniang (alcoholic rice porridge/pudding). There are other varieties of Qu specific for different types of fermentations, such as in the production of Jiang you (酱油 soy sauce), Cu (醋 vinegars), Sufu (豆腐 fermented bean curds) and Doubanjiang (豆瓣醬 fermented bean pastes). Qu is the direct Chinese counterpart of the more widely known Japanese fermentation starter called Koji(麹 or糀), although Qu predates and differs from it slightly.

Jiuqu consists of a complex mixture of various molds, yeasts, and bacteria with their associated metabolites, cultured on a starch-rich substrate in a solid state fermentation process. They are typically stored and sold in the form of dried bricks (Daqu), balls (Xiaoqu e.g. Shanghai Yeast Balls), powders or as dried grains (Red Yeast Rice). The most common organisms found in Jiuqu are the filamentous molds Aspergillus oryzae and Rhizopus oryzae and the amylolytic yeast Saccharomycopsis fibuligera. Amylolytic and proteolytic enzymes are the most abundant metabolites isolated.

Although the art of making Jiuqu is a traditional practice of the Chinese that can be traced as far back as the Shang Dynasty (17th to 11th century BC), it can now be technically classified as a type of biomolecule manufacturing process. Jiuqu preparation serves two parallel functions, the growth of the microbial species and their generation of enzyme metabolites. Both are dried gradually on the substrate, ensuring their viability for anticipated reactivation when the Jiuqu is added to a new source of water and nutrition. Jiuqu is therefore a source of both microbes and enzymes. The addition of Jiuqu to a cereal or pulse-based solution initiates the breakdown of carbohydrates, proteins and lipids into CO₂, ethanol, organic acids and various other metabolites. This complex process of simultaneous catabolism and fermentation, often termed parallel or mash fermentation, is at variance with the beer and wine processes typical of the western world.

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