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At the beginning of the Meiji era (1868-1912), a group of breweries hired chemists to study fermentation methods, and to invent better machines to increase polishing. As a result of their work, the process of selecting and isolating yeast was discovered, and also how to make lactic acid. These discoveries made it possible to simplify the manufacturing process and to better control the fermentation.
In order to prevent the development of airborne yeasts, two steps were taken: lactic acid mixed with water was added to the shu-bo tank at the beginning. Then, about 12 hours later, the selected yeast is added and takes up all the space. This is a revolution in the process, because these two discoveries prevent the multiplication of undesirable and uncontrollable yeasts and bacteria.
This is now the most common method of making sake because it is the less risky, the easiest and the fastest method.