Sake is brewed in a strung out process that can take quite a long time but none of the steps are particularly difficult. In the traditional method, brewing sake starts with the rice and its milling. The objective is to remove the outer layers of the rice which cause sake to be less stable and to have harsher flavors. These layers contain the bran and the highest concentrations of oils, fatty acids, proteins and minerals like magnesium and iron. Table rice (white rice) is generally milled to around 93% of its original size. Sakemai (Sake Rice) is usually milled somewhere between this for futsu-shu (table sake) and 35% for the most refined Daiginjo. Removing these components leads to a more stable and refined sake.
Once the rice has been milled to the proper level we need to steam the rice. We used steamed rice both for making koji and to directly add to the brew. In order to steam the rice properly we need to first wash the milled rice to remove the outer layer of rice flower, talc or whatever may be on the rice. After a good washing the rice is soaked to absorb the needed amount of water for proper steaming. This amounts to about 30% by weight. The higher the milling rate the faster the rice will absorb the desired amount of water. Kurabito (brewery people) working with the most highly polished (Milled) rice often use a stopwatch to time the soaking period so the rice does not take on too much moisture. Here the goal to get enough moisture into the rice so that the steaming process gelatinizes the rice by heating the water already there. If the rice has too much moisture it will become soggy / mushy during the steaming process and will not form a nice home for koji.
With the rice properly washed and soaked it can now be placed in the kettle for steaming. The kettle is lined with cloth and the rice is added in layers so the steam has natural diffusion layers. We don’t want the steam to drill a tunnel through the rice thereby reaching only a small portion. Most brewers steam the rice for somewhere between 40 to 60 minutes. Once the steaming is complete, the rice should be firm and chewy without being overly sticky. At this stage the rice is either used for koji production or goes straight into the brew after cooling.
Steamed rice to be used for koji production is cooled down only to about 115F (45C) while it is being mixed and stirred to break up all chunks. When the rice is mostly chunk free and has cooled to 115F, koji-kin (Aspergillus Oryzae) is sprinkled over the rice and mixed in to inoculate the rice. The mold is then cultivated over the next 44 to 54 hours to produce koji; the mold covered rice that looks like small fussy white pillows. Koji provides the enzymes that convert rice starch to sugar and break down proteins into peptides and amino acids. Having produced koji, it is time to create the moto.
The moto is the initial starter for the brew. The most common method used for the moto is sokujo moto. Sokujo generally takes one to two weeks; beginning with koji, rice, yeast, lactic acid and water. All combined, the koji enzymes break down the starches to sugars and the yeast goes through a multistage process, first aerobic than then anaerobic. In the aerobic stage the yeast build up their cell walls and then reproduces to create more yeast through a budding process. The cell wall build up and reproduction is important to have enough yeast in later stages where there is much more sugar to process. Next, the anaerobic stage the yeast has use most of the oxygen in the moto and begins to process the sugar into alcohol and carbon dioxide. The anaerobic stage continues until virtually all the sugars have been consumed and there is no more being created by the enzymes working on the starch. The goals of the moto are multiple. First, the moto is to build up the needed yeast for the brew. Second, the moto is to develop the lactic acid needed to protect the brew; in sokujo, lactic acid is added rather than cultivated. Third, is the cultivation of other bugs that provide more complex character to the sake.
Once the moto is complete, a series of three additions are made to convert the moto into the moromi. These three additions are done over a period of 4 days. The three additions are:
- Hatsuzoe – the first addition, day 1
- Nakazoe – the second addition, day 3
- Tomezoe – the third and final addition, day 4
In each of these three additions, koji, steamed rice and water are added. Koji and water are added at the beginning of the period followed about 12 hours later by steamed rice and water. After Hatsuzoe a day of rest is allowed. This day of rest (day 2) is Odori (the dancing ferment). Odori is followed by Nakazoe and Tomezoe, each taking one day with additions of increasing size but with the same pattern as Hatsuzoe, koji and water followed by steamed rice and water 12 hours later.
With the end of Tomezoe, the main ferment, Moromi, begins. Having added all the koji, rice and water, it is now left to the enzymes and yeast to do the work. The yeast, as we mentioned above, go through stages, aerobic cell wall build up followed by reproduction through budding and anaerobic processing sugar into alcohol and carbon dioxide. They were mostly in the anaerobic stage at the end of moto but the introduction of the three additions along with continual stirring provides a complex environment where some yeast may be building cell walls, some budding and some producing alcohol. By the latter half of moromi, however, the yeast have almost completely settled into their anaerobic efforts, making alcohol.
Yeast are more efficient in their transformation process than are the enzymes at the moromi temperatures (40F to 60F, mostly on the lower end). As quickly the enzymes create simple sugars yeast pick them up and convert them to alcohol and carbon dioxide. This produces a brew with very low levels of sugar which help the yeast to continue to remain healthy. High levels of sugar in solution are toxic for yeast. Moromi lasts for from around 14 days to 30 days.
At the end of Moromi, the brew is pressed to force the sake from the kasu (lees). This removes much of the solids but not all. After settling, sake is filtered and pasteurized. At this point the sake is allowed to age and condition for a few months or more. When it is time for bottling an adjustment is often made to bring the alcohol level in line with standard sake of about 15% to 16%. Genshu is sake that has not had this adjustment made, leaving it at from 18% to 22%.
Once the Sake has aged for some time it is ready to be bottled. During bottling the sake is also pasteurized for a second time. This is to ensure that no bugs remain that will continue to transform the sake. With the sake now bottled and pasteurized it is now ready to sell.