How is Sake Made?—-The Fermentation

I have been blogging about how sake is made and it has been quite the journey. Here are links to previous blogs about making sake:

• How is Sake Made?---The Rice
• How is Sake Made?---The Water
• How is Sake Made?---The Koji
• How is Sake Made?—-The Yeast

Today's blog is about the fermentation, which is the penultimate step in sake making.
3-Step Fermentation or Sandan Jikomi
The fermentation step in sake making consists of three steps known as sandan jikomi.

• In the first step, a mix of shubo (source of yeast), steamed rice, koji, and water sit in a tank and ferment over a day
• Next, the brewers add a batch of steamed rice, koji, and water two more times to gradually increase the fermenting mash volume

The above three steps occur over a period of three to four weeks. The temperature of the fermentation is kept between 8 ^oC to 10 ^oC. The active fermentation produces enough alcohol in the mash to prevent any microbial contamination.

In the sandan jikomi two processes take place at the same time. The koji’s enzymes break down rice starch into sugar, and the yeast ferments the sugar into alcohol.

The beauty of this process is that since the sugar is fermented into alcohol as it gets produced, the mash's sugar concentration stays at an ideal level. Therefore, these parallel processes, together with the 3-step fermentation, actively support an efficient fermentation activity, producing a 17 to 20% alcoholic content by the end.
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