Sake is a Japanese alcoholic beverage, made mainly from fermented rice.
The word sake in Japanese actually refers to any alcoholic beverage, including wine, beer, liquor etc. so the appropriate term for the Japanese drink is nihon-shu, literally Japanese-alcohol. Other Japanese alcoholic drinks exist, like sho-chu and ume-shu, but we will talk about them separately.
Sake is made primarily from rice and water, which interact with microbes known as Koji‐kin (a mold) and kobo (sake yeast). Only highly polished rice goes into making sake and lends the drink its refined character.
Japanese rice can be roughly classified into two varieties. The first is ordinary table rice, generally eaten by most people, it encompasses a number of sub-varieties that are classified by how they are cultivated and the region in which they are grown.
The second variety, sakamai is used exclusively for sake production. While ordinary table rice can be used to make sake, it is typically made from the higher quality and more esteemed sakamai. The grains of this variety are larger and softer than ordinary table rice. Sakamai is also more expensive since it grows only in certain areas and requires more complex cultivation techniques.
These days new types of sake rice are being developed while heirloom varieties are being revived in many areas of Japan. In 2010 there were at least 95 different types of rice for brewing sake being grown in Japan.
Water quality is extremely important because the mineral content of the water affects the taste of sake.
Semi-hard water is ideal for sake production due to its lower iron and manganese content. Since Japan experiences significant annual precipitation and boasts ample high-quality ground water across the country, excellent sake can be produced in nearly every region.
Koji-kin is a mold that converts starch from the rice into sugar, which the kobo yeast feeds on.
During the process of brewing sake, a particular kind of yeast, called saccharomyces cerevisiae, converts sugar to alcohol. The Japanese term kobo means ‘mother of fermentation’ whereas the Latin name means 'beer's yeast'.
The brewing process begins with polishing hulled rice, the main ingredient. As it passes through a special polisher, the proteins and bran that can produce off flavors in the sake are removed. This phase is very important and impacts the sake quality level.
The polished rice is washed in water to remove the bran and is left to steep in water. When the grain has absorbed 30% of its weight in water it is steamed.
One batch of steamed rice may be used to make koji, yeast starter, and to feed the moromi mash.
Spores of the aspergillus oryzae mold (koji-kin) are added to the steamed rice, which is then incubated to produce koji.
Then shubo is made by mixing steamed rice, water, koji, and yeast. It contains large amounts of yeast, which promotes the moromi fermentation process.
Finally koji, steamed rice, and water are added to the shubo and then left to ferment again.
A process unique to Japanese sake brewing takes place. It’s a three-step fermentation process known as sandan shikomi. On the first day, koji, steamed rice, and water are added to the yeast starter (this addition is called hatsuzoe). The mixture is left to stand on the following day to allow the yeast to slowly multiply (this step is calledodori). On the third day, the second batch of koji, steamed rice, and water is added to the mixture (this addition is called nakazoe). Then finally on the fourth day, the third batch is added to the mixture (this addition is called tomezoe) to complete the three-part process.
From this point, the koji-kin will convert the starch in the rice into glucose, which the yeast will then use to create alcohol and carbon dioxide. The conversion of starch to sugar and sugar to alcohol takes place in parallel all in the same tank. This is known as "multiple parallel fermentation," and is a process that is entirely unique to sake.
Once the moromi is completely fermented, it is passed through a press to separate out the sake lees. The sake is then filtered, pasteurized, and placed in cold storage where it matures before being bottled.