Sake is produced from Rice, Water, Koji mold, Yeast, and sometimes additional alcohol.
The brewing process is much more similar in style to beer than to wine, however the actual production itself resembles wine-making more than beer brewing.
The rice is cultivated, harvested, taken to the sake brewery (Kura) and is milled (Seimaibuai) to remove the outside layer of the rice grain. The useful part is the starchy interior or Shinpaku which will produce the best and purest sake. The more the rice is milled the higher the quality, but the lower the yield.
Rice itself, like barley used in beer production, contains no fermentable sugar, the energy for germination is contained in the starch. To convert the long molecules of starch into shorter sugar molecules, which the yeast can then convert into alcohol, a mold known as Aspergillus Oryzae or Koji is used. The koji break the starches into glucose and other sugars, and the yeast can then act on the sugars and produce alcohol.
Water is very important for sake production and like beer is a big factor in the resultant flavor profile. Top kura are historically located near sources of pure water, or those regions with a high snowfall.
After polishing the rice is soaked in water and then steamed. A portion of the rice is taken and used to grow the Koji mold, while the rest of the rice will be used during the brewing process. Starting the fermentation is a process done over 4 days: The fermentation is started using a small amount of the koji mold, yeast, and rice in a large vat; over the next 4 days the vat is incrementally filled with more rice, koji, and water. This allows for an increase in the volume of fermenting mash without weakening the concentration of yeast.
The mash undergoes Multiple-Parallel Fermentation (Heikoufukuhakkou) as the Koji breaks starch into sugar and the yeast converts sugar into alcohol. These two processes occur at the same time in the same tank. It is a process UNIQUE to sake production.
After fermentation the mash is pressed to separate the solids from the sake, the sake is then left to settle for a few days and is then filtered. Most sake is pasteurized at least once before bottling.