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Making sake: preparing the mash (moromi)


Because rice does not contain sugar, the rice starch has to be converted to sugar. To accomplish this, it is necessary to use kōji (a mold culture that converts starch to sugar).


However, to make sake, another microorganism is needed so that the sugar can be converted to alcohol. That’s where kōbo (yeast starter culture) comes in to play its role. It converts sugar to alcohol.


Sake is made with both kōji and kōbo mixed together in a single vat. In other words, both stages (starch → sugar → alcohol) take place in a single container. This method of brewing, called “multiple parallel fermentation,” is unique to the brewing of sake.




Three-stage preparation of moromi
Sake is produced by adding steamed rice, water, and kōji to the shubo, and fermenting the mixture. The mash formed by the combination of these ingredients is called the moromi. When the moromi is pressed, the liquid obtained is sake. The moromi mash is prepared in three stages.


Not all of the ingredients are combined at once to make the moromi. On the first day, just one sixth of the total quantity of each ingredient is used. This first addition is called hatsuzoe. As the kōbo propagates in the vat, alcohol is produced by the fermentation.


On the second day, however, nothing more is done. At this point, it’s a matter of patiently waiting for the kōbo to grow. The second day is referred to as the odori.


On the third day, more steamed rice, water, and kōji are added. This time, one third of the total amount of ingredients is added. The second addition is called nakazoe.


Finally, on the fourth day, the remaining steamed rice, water, and kōji (one half of the total amount) are added. This third addition, called tomezoe, completes the preparation of the moromi.



The reason why the full amount is not added at the start
There is a reason why the full amount of steamed rice, water, and kōji is not added right from the start. The purpose is to eliminate the possibility of unwanted bacteria getting a foothold and propagating in the moromi.


There is a high concentration of live yeast in the shubo (yeast starter). When steamed rice, water, and kōji are added, it becomes diluted, giving unwanted bacteria and yeasts in the air an opportunity to propagate. Since this would adversely affect the quality of the sake, the kōbo (yeast) culture is always maintained at full strength.


There is also a reason why the mixture is given a rest on the second day. Particularly at the early stage, it is necessary to allow two full days for the kōbo to propagate thoroughly and regain full strength.


By the third day, the kōbo has regained momentum, and an additional one third of the ingredients can be added. From that point, on the fourth day, the remaining portion of the ingredients can be added.


Also, because the kōbo is constantly maintained at full strength, it is always kept “hungry.” As fermentation proceeds, with the addition of steamed rice, water, and kōji to this kōbo-rich mixture, sake with a high concentration of alcohol is produced.


After passing through the hatsuzoe, odori, nakazoe, and tomezoe stages, by the fourth day alcohol concentration reaches 20%. Such a high concentration of alcohol resulting from a fermentation process, without distillation, is achieved only in the brewing of sake.


The preparation of the moromi is completed in this way, but at least 15 days are needed for the entire fermentation process. Up to 30 days are required for the moromi when making high-grade sake such as ginjō-shu. During this period, numerous checks are performed to test the taste and aroma of the sake. When the moromi is eventually pressed, new sake is obtained.

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