Even steamed, rice does not contain enough water to produce "juice" during fermentation. It is necessary to add spring water throughout the production process. The water is a crucial element, and if sake breweries exist, it is often thanks to the quality of water in their regions.
The water comes from deep wells or natural sources, and should have constant physical and chemical properties. Sake producers speak of hard water (Kosui) or soft water (Nansui). Potassium and magnesium are essential compounds for yeast multiplication and proper development of Koji. Other elements should be avoided: a ferruginous or manganese-rich water will hinder fermentation, darken sake, and affect its flavor.
There are about 80 varieties of sake rice in Japan. Among the most famous, the Yamadanishiki, also called the "king of sake rice". It is very fragrant and is used for the production of many Daiginjo. The Omachi rice is less fragrant, with a special more earthy flavor. It is used for the production of many sakes that are enjoyed hot. The Goyhakumangoku gives a smooth and clear sake. Dry, slightly fragrant.
Koji is a microscopic fungus scientifically called Aspergylus oryzae. Koji develops on rice and produces spores that secrete the enzymes able to digest the large starch molecules into simpler sugar (saccharification). These simple sugars can then be fermented. In comparison, the sugars in the grape juice can directly enter into the fermentation process.
The Koji is kept by brewers, and used in a particular room called Kojimuro.
They convert sugar into alcohol (fermentation), and represent a key element in the production process. Each specific strain of yeast will produce its own spectrum of chemical compounds by forming various alcohol esters ginving to sakes its flavors and nuances.
The Kura is organized into three classes of workers: the Kuramoto, which owns and maintains the land and brewery; the Toji, who is the master brewer; and the kurabito, who are seasonal employees.
The work of Toji is a respected position, and is particularly interesting to describe. It is hard work, and competition is fierce to enter into this field. Toji usually learn their skills in one of the 25 Toji schools (called Ryuha). They are spread throughout the islands, usually in mountainous areas. The teaching is strict, and rather secret.
The methods are not formally unveiled to students, and the only way to learn the technique is to observe and interpret the gestures of instructors. Research centers, and higher education for professionals, are also found accross Japan.
Because of its north to south extent, Japan has a varied climate, ranging from a cold and very snowy area in the North, to mild temperatures and shorter winters in the south. The four seasons are well defined, and temperature changes are favorable to the cultivation of rice. In summer, semi-tropical climates (very rainy and hot), promotes the growth of plants. After the rainy season, higher temperatures (over 20°C) for one to two weeks, promotes the maturation of rice. This is the moment when rice is acquiring its character and uniqueness.
Rice is harvested once a year in Japan. Harvesting takes place in autumn, and sake is prepared in the winter. During the production process, a sufficiently cool temperature is better to not alter quality of sake.
Sake is produced in the whole archipelago, and some regions have a very good reputation. This is the case of the Nada area, near Kobe, where water is naturally filtered through the granite canyons of Rokko mountain, or the Niigata region, which is mountainous and snowy, facing the ocean, and renowned for the high quality rice and very pure waters.