In the intensely cooked white rice, the conidia of Aspergillus are moved and then kept warm. Mycelium will grow lushly on the rice grains, which is koji. The strong action of amylase from Aspergillus saccharifies rice starch. Therefore, it has been used as a raw material for sugar together with malt since ancient times to make wine, liqueur, soybean paste, etc. Those who use wheat instead of rice are called wheat koji.

The origin of distiller's yeast is unknown. The earliest text about distiller's yeast may be "If you want to make wine, you can only use the tillers" in the Zhou Dynasty work "Book of Records". Analyzing from scientific principles, distiller's yeast actually evolved from moldy grains. The production technology of distiller's yeast was comprehensively summarized for the first time in the "Essentials of Qi Min" in the Northern Wei Dynasty, and reached an extremely high level in the Song Dynasty. The main manifestations are: complete varieties of distiller's yeast, perfect technology, and the saccharification and fermentation power of distiller's yeast, especially the southern version of Xiaoqu. Modern distiller's yeast is still widely used in the brewing of rice wine, liquor, etc. In terms of production technology, thanks to the mastery of microorganisms and theoretical knowledge of winemaking, the development of distiller's yeast has reached a new level.

The original koji is moldy or sprouted grains. People improved it and made koji suitable for brewing. Due to the different raw materials and production methods used, as well as the different natural conditions in the production areas, the varieties of koji are rich and colorful. Roughly during the Song Dynasty, the types and manufacturing techniques of Chinese distiller's yeast were basically finalized. Later generations made some improvements on this basis. The following are the types of Chinese koji:

1. Classification system of koji

Based on the raw materials for making koji, they mainly include wheat and rice. Therefore, they are called Maiqu and Rice Qu respectively. There are many types of koji made from rice, such as koji made from rice flour, red koji or black rice koji made from steamed rice, and rice koji (Aspergillus oryzae).

According to whether the raw materials are matured or not, it can be divided into raw wheat koji and cooked wheat koji.

According to the additives in the koji, there are many types. For example, those that add Chinese herbal medicine are called medicinal koji, and those that add legumes are called bean koji (peas, mung beans, etc.).

According to the shape of the music, it can be divided into Daqu (straw bag song, brick song, hanging song), Xiaoqu (cake song) and Sanqu.

According to the source of the microorganisms in the koji, it is divided into traditional koji (natural inoculation of microorganisms) and pure koji (such as rice koji inoculated with Aspergillus oryzae, Rhizopus koji inoculated with Rhizopus, and koji inoculated with Aspergillus niger) ).