First comes rice polishing. Rice contains starch and nutrients like proteins, fats, amino acids, vitamins and minerals. Too many nutrients can sometimes cause unpleasant flavors in the final product. Rice polishing removes unwanted nutrients while leaving the much-needed starch to be converted into sugar (saccharification) which then is converted into alcohol (fermentation). Brewers decide what profile of sake they wish to create and that determines how much the rice will be polished.
As friction heat may cause rice to break down, it is polished very slowly. It takes approximately 72 hours to polish rice to 40% of the original grain. After the rice is polished it is stored in a bag for at least two weeks to rest. During this 'rest' period the rice absorbs moisture from the air and achieves a more balanced moisture content for the following stage.
Nothing is wasted in the brewing process. The byproduct of polishing the rice grains is a powder, or nuka, that can be used for animal feed, fertilizers, as well as in food products like rice crackers, rice noodles, rice flour or even pickles.
This process can be automated using a rice washing machine. The polished rice is washed and then sent to a soaking tank. Once the desired absorption rate is obtained the water is drained. Breweries can also choose to carry out the washing to draining process by hand. This labor-intensive process, known as gentei kyusui, is the art of carefully limiting the water absorption of the delicate small grains. Limited absorption is obtained by delicate hand washing, precise to the second soaking times and quickly but gently draining.
The object of steaming the rice is to make the starch within the rice grain more soluble and reactive to koji enzymes. To steam rice brewers can choose to automate or carry out by hand. When automated, the rice is sent to a continuous rice steamer where the rice travels on a conveyer belt for approximately 50min. Steam is blown onto the rice and then sent to a cooler. If done by hand, the rice is carefully placed into a traditional steamer called a Koshiki. Water is heated in a vessel below the koshiki and steam is applied for about an hour. Once steaming is complete the rice is carefully extracted from the Koshiki and left to naturally cool.
Steamed rice is spread out on cloth for cooling it. Cooling machines can also be used for a large quantity.
A very labor-intensive and meticulous process when done by hand. In the photo to the right, the worker is sprinkling koji mold in powder form onto steamed rice. The koji mold is then watched over and manipulated to grow onto each and every grain of rice for about two days.
The next step is preparation of starter mashof the starter mash (shubo / moto). A yeast starter is created specifically to cultivate active healthy yeast cells in mass quantities while maintaining proper lactic acid levels. There are many ways to make a yeast starter. The most widely used methods are sokujo, yamahai and kimoto.
The main mash is pressed to separate the liquid from remaining solids. The pressed liquid is clear and is referred to as sei-shu (clear sake). The rice solids are referred to as sake kasu (similar to lees and wine). Sake kasu (rice solids) are often used in many other industries. Sake is pressed by one of three main methods; gravity (drip pressing), Automated pressing machine (Assaku-ki aka Yabuta Press like shown in photo), or by Fune (traditional pressing). Another method of coarsely pressing the sake results in a style known as Nigori. Brewers have a choice of which style to used when pressing: Assaku-ki (aka Yabuta Press), Fune Press, or Gravity press(Fukurozuri or Tobinkakoi)
After filtration, sake is pasteurized and stored for maturing in a tank. It takes a half to one year for sake to mature. Storage is at 60 degrees or lower. Maturation varies tank by tank. To obtain quality and taste that a producer wants, sake in these tanks will be blended for the final product. Until sake is bottled, it is controlled under strict conditions to gain best quality.
Depending on the final product desired, brewers have several choices to make after pressing the sake. Typically, after sake is pressed it is pasteurized, stored, filtered, diluted, pasteurized a second time and then bottled. If the brewer decides to omit a step in the process it creates a specific style of sake. After bottling, quality is easily deteriorated by high temperature and/or light. It is highly recommended to store sake in a dark and cool place. Once opened, consume within 1 - 2 weeks.