Sake is made using 2 microorganisms, koji (麹) and yeast (酵母). I described a little about koji in my last posts- the next step in brewing is to start a yeast culture (300-400 L) using koji-rice, water, rice, and of course, yeast. This is called the moto, and takes from 1-2 weeks to make depending on the grade sake being made. In our first batch of sake this year, we are making honjozo (本醸造) and will use a 1 week old moto. After mixing all the ingredients, the yeast start multiplying very quickly, so controlling the temperature is very important. After a couple of days, our moto was proceeding a little too quickly (consuming too much sugar) so we had to slow it down using a large aluminum container filled with ice.
The moto gives off a great smell, very fruity, with hints of bananas, and is very active.
In a few more days it is going to be ready, and we will use it to start the true fermentation for the first batch of sake, called soe shikomi (添仕込み), which requires the addition of more koji-rice, water, and regular rice.