How is Sake Made?—-The Yeast

I took a little break from my journey on how sake is made, but I am back and the next step is all about the yeast.
The Yeast
This step is called the making of the mother culture or the shubo. In this step, the brewers will use a relatively small portion of the mash, koji, water and yeast to create the active yeast culture.

This is the starter for the fermentation of the main mash. The shubo needs to be acidic in order to prevent the growth of unwanted microbes. Sake brewers use one of two methods to create the acidic shubo. They use either the Kimoto/Yamahai-moto or the Sokujo-moto method.
Kimoto/Yamahai-moto Method
The traditional way to acquire acidity is to cultivate natural lactic acid bacilli which exist in koji or in the wooden tools and tubs. The brewers first mix steamed rice, koji, and water at around 8°C and gradually increase the temperature to cultivate the lactic acid bacilli for about two weeks. When the mixture reaches a significant level of acidity, brewers add the yeast to start the alcoholic fermentation. Another two weeks later, the acidity and alcohol kill the majority of the microbes except for the yeast. This type of shubo makes sake with a strong body and complex flavor. Oftentimes, if the sake is made using this method it will be so indicated on the label.

Sokujo-moto Method
The main method of boosting the acidity in shubo today is to add lactic acid. This process is a relatively new technique, invented in the early 1900s. It facilitates the shubo making by eliminating the traditional process of growing lactic acid bacilli. This way, the time needed to complete the shubo shrinks down from 4 weeks to 2weeks. The resulting sake tends to taste lighter than the sake made with traditional style shubo.

Can you believe that all of these steps must be accomplished before fermentation begins! Next blogpost will be on fermentation.
References:
1. Japanese Sake, How is Sake Made?
2. Harper, Philip, The Book of Sake A Connoisseur's Guide, Kodansha International, 2006.
3. Sakaya, Sake Making Steps