The exterior of unpolished sake rice contains fats, proteins and other elements that can affect the flavor and aroma of the final product. Polishing the rice to remove the exterior helps to bring out the full flavor of the rice.
The polished rice is washed to remove surface impurities such as bran, and then soaked to boost the moisture content. The soak period is carefully calibrated depending on the condition of the grains. This requires considerable experience and expertise.
Steaming begins once the required moisture content is attained. Steaming promotes propagation of the koji mold. The steaming process is a key determinant of the quality of the final product.
Koji is responsible for one of the most important aspects of the sake-making process: converting rice starch into glucose. The koji is sprinkled evenly over a bed of steamed rice and left to propagate in a special chamber maintained at high-temperature and humidity. The propagation process generates heat, adding to the temperature inside the chamber. The rice has to be turned over at regular intervals to regulate the heat and prevent excessive temperatures that could hinder propagation.
The yeast starter transforms the glucose produced by the koji into alcohol. This is where the sake-making process really begins.
Making the moromi represents the core of the sake-making process, where the koji and steamed rice are carefully added to the live yeast starter and water in three separate stages, maintaining optimum conditions for the starter. The interaction between the moromi and the starter promotes alcohol fermentation and helps develop the distinctive flavor and aroma of sake.
The final step process involves extracting sake from the moromi. While this would normally be achieved via mechanical pressing, the Eiga junmai daiginjo and Tokubetsu (Special) junmai sake varieties employ a manual gravity drip extraction method, known as fukuro shibori, that eliminates extraneous flavors for ultimate purity of flavor.