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The "Nihonshu", or Japanese sake is a fermented beverage made from rice and containing around 15% alcohol. Its production is a complex process that takes place in a brewery called "Kura" in Japanese. The master brewer, or "Toji", is in charge of production. He is assisted in his task by the "kurabito".
For a producer of sake, the year is divided into two main periods: the warmer months, devoted to the cultivation of rice, and the coldest months for the production of sake.
Koshinohana brewery, in Niigata
Rice is the main ingredient of sake (with water and yeast). Before entering the production process, it must be rid of its brown cuticle and milled. Vertical grinders are used to brush of the outer layers and keep only the core of each grain. The rice polishing degree is called "semaïbuaï" in Japanese. It determines the class of sake, without entirely prejudging its taste. During this step, rice may lose up to 75% of its weight.
Note that indications about the degree of polishing, is always considering what percentage of material remains.
If 40% of the outermost layers of a grain of rice are removed, the "degree of polishing", the samaïbuaï will be "60%" (i.e. what remains).
Rice stripped of its cuticle and then polished before entering the production of sake
Polishing is an important step because it concentrates the starch that is more present in the core of a grain of rice, unlike the periphery that contains more fatty acids, proteins and amino acids. So, the more rice is polished and more starch will be concentrated.
Once polished, rice is washed, moistened and then placed in the "koshiki", a traditional cooking instrument. It is cooked slowly with steam coming from the bottom. Once cooked, rice has a very peculiar consistency: it is soft on the inside, and firm on the outside.
Washing and cooking rice for preparation of sake
Once cooked, rice is transferred in a special room called "Kojimuro", where temperature and humidity are closely controlled. Rice is manually seeded, each grain being carefully separated from the other in order to favor exposure to ferments. This prepares the rice for the next crucial step in preparation: the rice will receive Koji.
End of rice steaming and transfer in the kojimuro
What is Koji and what is its role ?
Rice contains starch, a macromolecule composed of sugar chains which cannot ferment as-is. It is essential to separate the chains into smaller sugars. This is done through a process called saccharification. Koji, a fungus classified in the type of aspergylus oryzae, is spread on the rice, develops and releases amylases, enzymes capable of transforming starch into simple sugars. These simple sugars can then be fermented into alcohol by the action of yeast.
Saccharification of stach by koji for the preparation of sake
Koji is in the form of a green powder; the strain is maintained on the rice. This powder is scattered over cooked rice and Koji will grow for three days. The mixture of Rice + Koji is stirred to promote the action of enzymes. After the process, rice is literally penatrated by koji.
Koji as a green powder is dispersed on the steamed rice
Electron microscopic view of the development of koji on rice grains
After three days, the action of koji allows the production of simple sugars. Then yeasts come into play. The toji prepares a starter of fermentation which is made of koji rice + the yeasts and spring water. This starter is called "moto". The yeast will grow and start producing alcohol and alcohol esters. The temperature increases and bubbles start forming on this mixiture.
Preparation of fermentation starter with yeast ("moto")
The fermentation starter is disposed in larger fermentation vats. Then the fermentation process itself starts and will last between 3 to 5 weeks. During this period, the contents of tanks are regularly mixed. Water and more cooked rice are added to feed the reaction.
Fermentation of rice in vats to produce sake
At the end of fermentation, the contents of tanks is collected and pressed. The remaining material composed of digested rice particles is called "kasu"; it is used in traditionnal japanese cuisine. Sake is then filtered (or not), pasteurized (or not). Six months later, sake is bottled and is ready to be enjoyed.
Pressing, filtration and bottling of sake