Sake is a brewed alcoholic beverage made from rice, water, koji mold and yeast.

RICE:
There are more than 80 different rice varieties which are grown and used for sake making in Japan.
Sake rice is different from table rice in both appearance as well as in its taste. A grain of sake rice is larger than that of table rice by 20%. Sake rice also has a white core called “Shinpaku” at the center of a grain. The white core affects water absorbability and other important factors for sake production.
Sake rice is polished before used. The outer layer of the rice contains nutrients like proteins, fats and minerals. These substances cause unpleasant flavors in the final product.
So, in general, the more the rice is polished, the better the quality of sake. As friction heat may cause rice to break down, it is polished slowly. For example, it takes 3 days to polish rice to 40% of the original grain.

Water is another critical ingredient affecting sake quality. More than 80% of any sake is made up of water. To make one portion of sake requires 30 to 40 times the amount of water. The quality as well as the quantity of water is a keen concern at each brewery. Almost all sake producers have their own water source such as a well or spring. Water with a low mineral content is called soft water, whereas water with a high mineral content is hard water. Most of the water sources in Niigata provide soft water. In general, sake brewed with soft water gives a smooth and clear taste.

Yeast converts sugar into alcohol and carbon dioxide. This bio-chemical process knows as “fermentation” leads to the creation of wine, beer, sake or any other fermented alcoholic beverages.
Grapes contain sugar in their juice. Add yeast and ferment it, and you will get alcohol, that is, wine. Unlike grapes, rice does not contain sugar and nothing happens if yeast is simply added to the rice. For sake making, they use another micro organism called Koji-kin (Koji mold, Aspergillus Oryzae), which produces enzymes in the steamed rice. The enzymes break down long chain molecules of starch in the steamed rice into glucose (sugar). This bio-chemical reaction is called saccharification. And then yeast converts glucose (sugar) to alcohol. During the sake fermentation process, these two bio-chemical reactions happen in parallel. This type of process is called “multiple parallel fermentation”, that is unique to sake making.
The steamed rice with propagated Koji mold and its enzymes are called Koji or Kome Koji (meaning rice Koji).

The quality of sake depends on both the ingredients and the production technique.
For wineries, the grapes used for wine have a decisive effect on the final product. The selection of the grape varietal and the quality of the grapes used are two of the most important factors for the quality and taste of wine. For sake making, however, the art of sake making is more important than just the rice. This is because the sake production process is so complex and most of steps correlate with each other. One mistake at any stage affects all the subsequent processes. It requires a masterly technique to accomplish each step and properly prepare work-in-process material such as steamed rice, koji and the starter mash. In that sense, the most important factor for a sake producer is securing the services of a skillful toji or what you would call in English a sake master or master brewer.

Sake brewing process chart

Sake brewing process chart2