Danjikomi is one of the brewing steps and means of making unfiltered Japanese sake where the yeast and rice are added over three steps to the yeast mash or moto (another term for sake producing yeast) to provide a mild environmental change for yeast to adapt to while not losing its productivity. In addition, it applies to the process itself and finished sake brewed using this process.
Three steps are called hatsuzoe (the first step), nakazoe (second step), and tomezoe (third step).
It was originally used as a synonym of sandan-jikomi (three-stage preparation).
The following is the general context of Japanese sake production, not academic or professional terms.
They could be considered synonyms.
It was the blessing of a skilled worker at a sake brewery from long ago who knew everything about malt and yeast even before modern science entered Japan. "Goshu-no-nikki" (a technical book on sake brewing) written during the Muromachi Period referred this method already at that time. This allows fermentation to progress without stopping the activity of the yeast until over 20% alcohol could be made by the end of moromi (raw unrefined sake) brewing. This high alcohol content is rarely observed in brewed alcohol, and Japanese sake brewery has unique world level technical skills.
It is the first step. It is the day one process for the Japanese sake brewery.
The brewery lingo abbreviates it as 'soe.'
The yeast is first transferred to a fermentation tank before a small amount of kakekoji and kakemai rice are added before adding water and stirring. The purpose of this process is to further increase the amount of yeast.
Kakekoji is the koji left aside for the moromi producing process.
The kakemai is the steamed rice that was left aside for the moromi (sake mash) process.
It is the day two process. It is to watch its progress without adding anything.
The reason for why a very small amount of koji and rice are introduced in brewing for Japanese sake is because the sole purpose of the danjikomi is to prevent sudden environmental change for the yeast. Increased quantities of ingredients make the environmental change bigger for the yeast.
Even if it is a small amount, the introduction of kakekoji and kakemai proves to be drastic for yeast, and yeast is laid aside for a day after soe to let it adapt itself to the new environment. This process is called Odori (dance). During the odori, bubbles slowly form on the surface.
For details about this foam, please refer to 'the form of Japanese sake foam.'
It is the second step. This is the day three process.
It is abbreviated as 'naka.'
Twice the amount of koji, steamed rice, and water is introduced compared to the hatsuzoe once the yeast familiarized itself with the environment with koji and steamed rice.
This is the third process. This is the day four process. Its abbreviation is 'tome'. Once seeing that yeast has familiarized itself with its environment, twice the amount of koji, steamed rice, and water compared to nakazoe are poured for fermentation.
The simple calculation may make it seem that the volume at this point is eight times the original volume, but actual amount is twenty to twenty five times the original volume due to the progression of fermentation. The size of fermentation tank should be decided considering that the volume of the product expands even more temporarily due to bubbles, when using the bubble-forming yeast. The tanks mainly used nowadays are 3 ton fermentation tanks with 10 ton capacity.
After tomezoe, cold water is poured into the hollow jacket of the fermentation tank or ice tied around it in the traditional method to control temperature and wait for the sake to finish. The method or number of days of temperature control differ between ginjo sake (high-quality sake brewed at low temperatures from rice grains milled to 60 % weight or less) and other sake, and takes a total of about three to four weeks. Please refer to 'Japanese moromi Production' for details.
Yondan-jikomi (Four Step Fermentation)
The current market has not only Japanese sake made with 'yondan-jikomi,' but five, six, and even 'judan-jikomi' (ten step fermentation), but traditional danjikomi is sandan-jikomi and no method with further fermentation exists.
Of course, it is possible in principle to extend sandan-jikomi into four, five and more steps by increasing the amount of yeast and steamed rice, doubling the amount of the previous step as steps progress such as hatsuzoe, nakazoe and tomezoe during the sandan-jikomi.
However, 'a possible method' and 'reasonable method' are different, and sandan-jikomi already achieves the purpose of danjikomi to adapt the yeast to the new environment and there is no need for fermentation beyond yondan-jikomi from the standpoint of sake quality.
On the other hand, Hiroshi UEHAEA, who was the former judge of the alcoholic beverages advisory council, stated that the fermentation becomes more rapid at the last stage of fermenting unfiltered Japanese sake, and sake became less stringent during the period when the rice-polishing ratio techniques was not refined and amazake (Japanese sweet rice wine) was poured in at the fourth stage (amazake yondan) to adjust it.
Many sake brewers appeared that supplied amazake at the fourth step for sweetness as the historical sanzoshu that had a huge volume of distilled alcohol with additional sugar became popular and its former brewers lessened. In another words, it is a method to supply dry sake with sweet flavor by adding amazake made by dissolving rice industrially with starch enzymes.
This reformed sake using this type of yondan-jikomi has bad taste and its quality and aroma disappear quickly because it adds undissolved matter to immature mash.
However, the following exceptions exist.
The Branding Scheme of Kuramoto (sake brewer)
Kuramoto probably kept in mind that consumers who did not know too much about Japanese sake tended to have an impression that more fermentation steps equaled better product that used a great amount of effort and time, and used that for branding in market research. However, representative sakes that are sold as daiginjo or submitted to Zenkoku Shinshu Kanpyokai (National New Sake Appraising and Deliberating Fair) are brewed with real care and use sandan-jikomi.
Confusion with Yondangake (the final fine-tuning of sake fermentation)
Yondangake (or Yodangake) means to add a small amount of steamed rice that has been saccharified by enzymes at the last stage of fermentation for in order to slightly adjust the alcohol level or mildness or dryness of the sake. Doing so increases the sugar level and mildness of unfiltered sake. This is just an adjustment made after the sandan-jikomi, and has a tendency to be misinterpreted as a further fermentation step. Such cases can be seen when a Kuramoto markets the sake as 'yondan-jikomi' to consumers who do not know much about Japanese sake and tend to misinterpret it.