Rice Polishing (milling)
Today, I would like to talk about rice polishing. Rice polishing is one of important step for Sake brewing, because the levels of proteins, lipids, vitamins and minerals are undesirable components. The level of rice polishing ratio is one of the criteria in the grading system of premium Sake. Polishing ratio is "精米歩合 (Seimai-buai)" in Japanese. If they say that "the polishing ratio is low", the rice is highly polished and remaining part of the rice is small. For example, in case that the polishing ratio is 35% (this is super premium sake), 65% of the rice is polished and only 35% remains.
The rice is polished by big vertical rice-polishing machine as below photo. This machine is developed in 1933. By using this machine, it became possible for brewers to use low polishing ratio rice. This machine is automated. In order to polish 600kg rice, it takes about 10 hours to reach 70% and about 45 to 50 hours to reach 50%. If 35%, it takes more time.
(Vertical rice-polishing machine: The photo from KIKUHIME)
(The photo is brown rice of Yamadanishiki before polishing. The bran has a lot of nutrients. This part is removed during polishing. The photo from Masuda Sake Company)
(This is major table rice Koshihikari. Some brewers makes Sake from table rice. The photo from Masuda Sake Company)
The main component of rice grain is starch. The outer layer of the endsperm contains proteins, lipids, vitamins and minerals. These are important nutrients for yeast and Koji to grow. Proteins are source of the umami taste of Sake, and make Sake more rough and heavy texture. If the brewers want to make rough and heavy style Sake, they select high polishing ratio like "70%". On the other hand, the berwers seek out to make a delicate, light textured Daiginjo, they select low polishing ratio like "50%".
(The photo is Yamadanishiki 50% polishing ratio. The photo from Masuda Sake Company)
(The photo is Yamadanishiki 35% polishing ratio. The photo from Masuda Sake Company)
When the target level of polishing ratio is achieved, the rice is coolded down and arrange the moisture content of the rice before washing. This purpose is to reduce cracking on the rice caused by an immediate temperature change when it is wached in cold water.
In case of low polishing ratio like 50%, 35% or much lower, it is labour intensive and takes much time, so, the price is higher than the other grade of premium Sake and they are regarded as super premium Sake. However, what I would like to tell you here is that the higher price Sake is not always the best Sake. If the brewer seek out to make more textured Sake, they will choice high polishing ratio. Polishing ratio is the important facter to decide the price, but, this is just one selection of some important facter to decide the taste which brewers seek out.