Wine shell, generally writing wine yeast. After intense cooking, the conidia of Aspergillus are transplanted into white rice, and then kept warm, hyphae will grow on the rice grains, which is called koji. Amylase produced by Aspergillus will saccharify starch in rice, so it has been used as raw sugar with malt since ancient times to make wine, sweet wine and soybean paste. Wheat instead of rice is called wheat koji.

The origin of distiller's yeast can't be verified. The earliest text about distiller's yeast may be "If you are distiller's yeast, you are only a tiller" in the Book of Scriptures and Numerology of the Zhou Dynasty. From the analysis of scientific principles, koji actually evolved from moldy grain. The production technology of distiller's yeast was comprehensively summarized for the first time in Qi Yao Min Shu in the Northern Wei Dynasty, and reached a high level in the Song Dynasty.

Mainly manifested in the following aspects: the variety of distiller's yeast is complete, the technology is perfect, and the saccharification and fermentation ability of distiller's yeast, especially southern Xiaoqu, is very high. Modern distiller's yeast is still widely used in the brewing of yellow rice wine and liquor. In terms of production technology, due to the mastery of microorganism and brewing theory, the development of koji has leapt to a new level.

The original koji was moldy or germinated grain, and people improved it to make it suitable for wine making. Because of the different raw materials and production methods, the natural conditions in the producing areas are different, and the varieties of Qu are rich and colorful. Roughly in the Song Dynasty, the types and production techniques of China distiller's yeast were basically finalized. Later generations made some improvements on this basis.