What role does distiller's yeast play in fermentation and wine production?

We all know that Baijiu is produced through microbial fermentation of grains, and distiller's yeast provides the initial microorganisms for fermentation, serving as the direct driving force of the entire fermentation process. Through fermentation, grains can produce different products such as wine, vinegar, and sauce in different microbial environments, and distiller's yeast directly determines the direction of fermentation - whether it produces wine or something else. Because of this, the Baijiu industry has a saying, "Yeast is the backbone of wine," which means distiller's yeast plays a role in setting the framework for fermentation and wine production.

All wine is produced through the fermentation of sugar. Fruits, due to their inherent sugar content, slowly produce wine under the action of natural yeast. However, for grain-based wine production, the starch in the grains needs to be converted into sugar under the action of microorganisms, and then fermented to produce wine. This step is called saccharification. Saccharification is a slow process in nature, so it is necessary to add distiller's yeast to provide microorganisms with saccharification function.

In ancient times, people promoted the germination or mold growth of grains by moistening them, and used the grains that had sprouted or moldy as distiller's yeast. Because these were loose grains that had sprouted or moldy, they were called "Sanqu". Sanqu was not conducive to the continued growth and enrichment of microorganisms, thus resulting in poor saccharification. In addition, Sanqu was also prone to breeding miscellaneous bacteria, which could disrupt the brewing process and even render the fermented product non-alcoholic.

Later, a process emerged to manufacture distiller's yeast into small yeast cakes or grains, known as "Xiaoqu". Xiaoqu has high saccharification efficiency and reduces the growth of miscellaneous bacteria. However, the microbial species in Xiaoqu are not diverse, and it mainly serves the function of saccharification and fermentation for wine production, with a weak aroma-producing function.

In 1324 AD, a master brewer named Guo Huaiyu emerged in Luzhou. He developed a new koji-making technique, shaping the koji into brick-sized blocks weighing approximately 3 kilograms each, thus earning the name "Daqu". Due to its excellent moisture and heat retention properties, Daqu is conducive to the growth and enrichment of microorganisms. Furthermore, based on its enhanced saccharification and fermentation efficiency, it can also facilitate the slow-growing aroma-producing microorganisms to gain sufficient growth time (the growth period of microorganisms in Xiaoqu is around 5 days, while that in Daqu is over 30 days). Therefore, the koji produced by Guo Huaiyu not only facilitates saccharification and fermentation but also possesses the important function of "aroma production".

Whether it's Luzhou Laojiao, Wuliangye, or Jiannanchun, which are all of the strong aroma type, or Maotai, which is of the sauce aroma type, or Fenjiu, which is of the light aroma type, all of them use Daqu as the distiller's yeast and are collectively referred to as "Daqu liquor". Correspondingly, liquor produced through fermentation with Xiaoqu is called "Xiaoqu liquor".