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Sharing some kimoto secrets

The microbial drama of the kimoto tanks

[The eve of battle]

Steamed rice, koji and water are all mixed in the mash tank. In the early low-temperature stages, the mash is nutrient-poor and the situation is ripe for warring factions of microbes. Quickly gaining strength among the rival groups are the nitrate-reducing bacteria. They enter from the water and rice, and by oxidising the nitrate salts in the water to nitrous acid they attack the other microbes present. However the film yeast and wild yeast that have infiltrated the tank as yet sustain no decisive damage.


[Lactic acid conquers all]

As the temperature begins to rise, the koji begins to produce nutrients. This allows the lactic acid bacteria, which have entered from the air, and the koji to become active. They begin to produce lactic acid from the glucose.
Most microbes dislike the acidic environment created by the lactic acid. The initially powerful nitrate-reducing bacteria are wiped out. Even the tough film yeast and wild yeast are vanquished by the double-barrelled attack of nitrous acid and lactic acid. Thus, the lactic acid bacteria conquer all to reign supreme within the fermentation tank, thanks to the acid they produce.


[And then there were none]

But the lactic acid bacteria have not achieved a lasting victory. One old theory is that the lactic acid bacteria themselves cannot withstand the harsh effects of the lactic acid they produce. Or do they fall before the attack of some new and unknown microbial champion? Whatever the reason, the lactic acid bacteria begin to quickly disappear. Who will be next to conquer the tank?


[Yeast victorious]
This is where yeast makes its appearance. It doesn't do well in the presence of nitrous acid and therefore lies low while nitrate-reducing bacteria are present, but with them gone, there is nothing for the yeast to fear. Strong in the presence of lactic acid, the yeast consumes glucose in this acidic environment where other microbes cannot survive. These nutrients fuel growth, making more and more yeast. Eventually the alcohol produced by the yeast kills off the lactic acid bacteria. And so in the end only the yeast, having endured bitter trials and emerged victorious, remains, in a mash with astonishing levels of purity. Yeast has won the day!




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