05 Main Mash

Main Mash

The standard ratios of steamed rice, koji and water placed in the fermentation tank are steamed rice 80, koji 20 (expressed as ratios of polished rice) and water 130. The total amount of rice placed in a single fermentation tank ranges from less than one metric ton to more than 10 mt. It is not all added at once, but in three steps over four days. On the first day, the amount of steamed rice and koji placed in the tank is equal to 1/6 of the total. Seed mash (shubo) is also added on this first day. Nothing is added on the second day, giving the yeast time to multiply. ON the third day, an amount equal to 2/3 of the total is placed in the tank, with the remaining 3/6 added on the fourth day. The temperature of the mix in the first step is 12°C, but this is gradually lowered to 10°C at the second step and 8°C at the third step. 

If the entire amount were added to the tank at once, the yeast would become too diluted, prolonging the time required to reach the right density for the proper fermentation of alcohol and allowing microbes to multiply, which could abort the fermentation process and spoil the mixture. 

In the main mash (moromi), the enzymes in koji dissolve the steamed rice and the yeast ferments the resulting sugars simultaneously in a single tank. The fermentation temperature is usually int eh range of 8°-18°C. The fermentation process takes around three to foud weeks, yielding an alcohol content of around 17%-20%.

Using a lower fermentation temperature of 12°C or less prolongs the fermentation time to around four to five weeks. Under these conditions, the action of the yeast and the process of dissolving the rice are retarded, reducing the acidity and resulting in sake with a highly fruity aroma and clean taste.