In this article and the next two articles, I will explain how sake is brewed, dividing the process into pre-brewing, brewing, and post-brewing. This blog is dedicated to Brewing: Fermentation.
For sake brewing, creating the fermentation starter is key. Water, steamed brewing rice, and Koji-rice are mixed in a small tank. Then brewers add yeast to it to create alcohol. Increasing the amount of yeast inside the small tank makes the main fermentation smoother with a lower risk of contamination. If it were not for this step, the mash would get contaminated easily by other microbes. This small amount of fermentation starter increases the acidity level in the mash to kill unfavorable microbes.
It takes about 2 weeks to create a yeast starter, and its quality greatly influences the flavor and taste of sake. To facilitate this process, the Sokujo method is the most common which is to increase the levels of acidity in the tank by adding lactic acid.
While the traditional version is called the Kimoto or Yamahai method, it applies the natural microbes in this process. Traditional sake types often have a thick and rich rice flavor with high acidity and a fuller body.
2. Main Fermentation
Next is the production of the main mash, moromi in Japanese. Water, rice, Koji malted rice, and the yeast starter are added to the main brewing tank. In a process known as san-dan-jikomi, the ingredients are added three times over four days. This allows the yeast and Koji to adjust nicely between each addition without giving any room for unwanted microorganisms to grow.
After the third addition of water, rice, and Koji rice, the mash is left to ferment for an additional 20-25 days.
In the next article, I will take a look at finishing: post brewing.