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Making sake: pressing, pasteurization, and dilution


Once the moromi is made, all that needs to be done is to press it to obtain genshu (undiluted sake). The process of pressing the moromi is referred to as jōsō. The day the pressing is to take place is determined by the tōji (chief brewer).


Once the freshly pressed genshu is obtained, it undergoes pasteurization and dilution. Pasteurization is performed to sterilize the sake, and the addition of water is necessary to adjust the alcohol content.


Pressing the moromi: jōsō

Making sake: pressing, pasteurization, and dilution

The moromi is composed of an alcoholic liquid part, the sake, and a solid part, the lees (sakekasu in Japanese). To separate the sake from the lees, the moromi needs to be pressed. This procedure is called jōsō.


Nowadays, pressing is almost always done by a machine. Bags containing moromi are lined up and pressure is applied horizontally to express the sake.


There is also a method of pressing called the fune method, in which the bags, once they are filled with moromi, are stacked in a sakabune (pressing tub) and pressed from above. This method is used for high-grade sake like ginjōshu. If a label says “sakabune shibori,” it means that the sake was pressed using the fune method.


The sake produced by the initial pressing, called arabashiri, is somewhat rough. The relatively consistent liquid produced in the next stage of the pressing is called nakatori. The sake expressed in the last stage of pressing is called oshikiri.


However, the sake pressed at these various stages is eventually mixed together, so it is difficult to compare arabashiri, nakatori, and oshikiri by drinking these separately.


Nigorizake and the removal of sediment
Freshly pressed genshu is not a clear liquid because it contains particles of protein and enzymes that give it a white, cloudy appearance.


These particles tend to settle out over a period of time to form a precipitate called ori. Naturally, given that ori contains protein and enzymes, if this precipitate is allowed to remain it will affect the quality of the sake.


In order to prevent this, ori is normally removed in a procedure known as oribiki. However, even when oribiki is performed, enzymes remain in the sake. For this reason, the liquid is passed through an activated carbon filter, producing clear sake.


There is a type of sake called nigorizake that is produced by omitting the oribiki procedure. To make nigorizake, the liquid is instead passed through a coarse cloth, so that ori remains in the sake. The resulting liquid has a white, cloudy appearance.


Pasteurization and dilution
Even when oribiki and activated carbon filtering are performed, a small residue of enzymes and yeast remains. To prevent this affecting the quality of the sake, the liquid is heated to a temperature of 60–65℃, neutralizing these active constituents. This procedure is called hi-ire.


Louis Pasteur, the French pioneer of microbiology, is famous for having discovered a similar low-temperature method of sterilization. However, some hundreds of years before Pasteur, in Japan’s Muromachi Period (1336–1573), this technique was being used in making sake. Biotechnology was as advanced as that back in those days.


After pasteurization (hi-ire), water is added to dilute the sake. The freshly pressed sake has an alcohol content of around 20% and needs to be diluted. The dilution procedure is called kasui.


After dilution, the sake once again undergoes heat treatment (hi-ire). It is then bottled while still hot to keep it sterile. Finally, the bottles are labeled, and the finished product is shipped.


There is a kind of sake that is not pasteurized, called namazake. Containing constituents such as live enzymes and yeast, it has a very fresh flavor. However, the enzymes make it perishable, so it is essential that it is kept refrigerated.

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