How is sake brewed?

Rice steaming stage

The steaming process helps to make the dissolving of rice starch easier and also provides a sterilizing effect.

Koji

The making of saké requires three important processes. Koji making is the first process of these three. Koji is made by sprinkling Koji kin, a mold used to break down starch into sugar that is used in beer, and shochu production also; The koji is sprinkled on steamed rice that has been cooled and partially dried. It usually takes around two days to make koji.

During this process starch within the grain begins its conversion to sugar. The substance is now ready for the yeast to begin their role of digestion of sugars and conversion to alcohol. This process of the breaking down of starch is important because the enzymes produced as a by-product of koji production have a major effect on the saké's taste.

The next two processes produce Shubo (yeast starter) and Moromi (fermentation mash), which are described below.

Yeast

Yeast is a Microorganism that converts sugar to ethanol (alcohol). Beer or Wine makers also use different species of yeast. Many of the best saké yeasts are often purchased from The Japan Saké Association. Additional proprietary yeasts have been developed by a number of different shuzo (saké breweries.) Utilization of these various yeasts significantly affects the flavor and aroma profiles of the saké.

Shubo

Yeast starter, also known as moto. This is a mixture of rice, koji, and water with an extremely high concentration of yeast cells. The process of making shubo is another critical step in the making of saké. The quality of shubo can dramatically affect the final quality of saké. At this point, usually lactic acid must be added to prevent bacteria from invading the cultivated yeast. This process usually takes about 15 days; however, some shubo requires 30 days to fully evolve if an older brewing style such as Yamahai or Kimoto, which forgo the addition of lactic acid, is being used. 

Moromi

Moromi is the final fermenting mixture or rice, koji, yeast, and water that ultimately the saké is pressed from. It is in the tank holding this mash where the double parallel fermentation process takes place. The koji mold within the mixture is converting starch to sugar and at the same time the yeasts are converting sugar to alcohol. This fermentation style is used only for Japanese saké.

During the fermentation of the moromi, the ingredients must be kept at low temperature, and the Toji always has to check and control this process in the 20-30 days remaining until the pressing. The care and observation of the Moromi (fermentation mash) is one of the most critical steps because the fragrance, S.M.V, acidity, level of amino Acids and alcohol content are all an outcome of how the moromi was directed.

Pressing

Pressing can be done either by a machine or by using hanging bags. After the Moromi is pressed, it will be separated into two parts: saké and lees. The lees (saké kasu) can be used to make items such as Japanese pickles (tsukemono), marinated saké lees on fish (kasuzuke), and/or saké lees pot (kasu-jiru).

Heating

Most saké is heated to approximately 156 °F for pasteurization to protect it from damage and changing during storage.

Addition of water

The original saké (Genshu) has an alcohol level of 20-22% so water will be added to reduce the alcohol content to 15-16%.