Vertical type rice-milling machine (縦型精米機)
A vertical type rice-milling machine was introduced around 1930 and originally used to produce sake.
In many cases it is wrongly written as '竪型精米機.'
The structure and function of this vertical type rice-milling machine is completely different from that of a horizontal rice polisher, which is often seen in 'a rice shop' to polish rice to be consumed by general households. This vertical type rice-milling machine is required to produce polished rice with high rice polishing ratios to be used for sake brewing.
With the arrival of this vertical type rice-milling machine, rice polishing technique innovatively advanced in the 1930s, which eventually brought the mass production of ginjoshu (high-quality sake brewed at low temperature from rice grains milled to 60% weight or less) in the 1980s.
Nowadays, in addition to the traditional horizontal rice polisher, this vertical type rice-milling machine is used to polish rice we eat.
It usually has a vertical cylindrical body with a height of about 10 meters and a width of about 5 meters, with a grinding stone called kongo roru (diamond roll) arranged inside. One theory is that it was named as 'vertical type' because this grinding stone is arranged vertically.
Kongo roru usually has two separate functions based on the grinding levels: coarse grinding and fine grinding.
In the early stage of rice polishing, kongo roru with coarse grinding function spins at high speed to remove outer shell from brown rice, and in the later stage of polishing when rice decreases its size to the point where it may be broken due to the heat generated by friction, kongo roru with fine grinding function spins at low speed to grind slowly into the central white-core structure of sake-brewing rice.
For sake brewers, the data on what shape the rice inside the machine is, what type of grinding stone is used, and at what speed it spins to polish rice is important know-how, almost corporate secrets, and nowadays there are many brewers that input the data by using a computer program and manage the rice polishing.