Rice-polishing ratio (精米歩合)

The rice-policing ratio ia specified in the National Tax Administration Agency's Notification No. 8 'Standard that regulates the method of manufacturing and quality labeling of refined sake' dated November 22, 1989 as follows:

The rice-polishing ratio is the ratio of the weight of polished rice to brown rice.'

According to this specification, 'polished rice' means rice grains produced from brown (unpolished) rice by removing the surface layers, such as bran and germ, and includes polished rice used for producing malted rice, and 'malted rice' is defined as 'polished rice in which koji yeast has been cultured to convert its starch into sugar.'
In contrast to the rice-polishing ratio, the ratio of weight of removed part to brown rice sometimes called 'polish percentage'.

Rice-polishing ratio of food rice
The average rice-polishing ratio of the polished rice which Japanese people ordinarily have in their eating habits is 90-92%. The reason why it is difficult to find the accurate numbers is that the rice-polishing ratio can be infinitely subdivided under the current circumstance where simple rice-milling machines are installed in some homes and some people eat brown rice without polishing and others eat rice after thirty percent threshing, half threshing or seventy percent threshing, and that after all the boundary of 'polished rice' depends on the sense of the consumer.

Because the rice grains gradually turn white as they are shaved, the rice polishing process is also called 'seihaku' (making white).

Rice-polishing ratio of rice for sake brewing
In sake brewing we seldom use the word 'rice shaving', but more often we use 'rice polishing'.

The rice-milling machines for food rice are greatly different in structure from those for rice for sake brewing and the efficiency of the latter has dramatically improved since the appearance of the vertical-type rice-milling machine early in the Showa period. For producing Japanese liquor ginjoshu (high-quality sake brewed at low temperatures from rice grains milled to 60 % weight or less) which requires rice polishing at such high accuracy as shin seimai buai (true rice-polishing ratio), computer-controlled rice-milling machines are sometimes used nowadays.

From 1989 to December 31, 2004 the rice-polishing ratios for Japanese sake were specified as follows:

Japanese liquor futsushu (ordinary quality sake)
No official regulations (in general approx. 73 to 75%)
Japanese liquor honjozoshu (a sake brewed with rice of polishing ratio not exceeding 70 % as main material and distilled alcohol of as auxiliary material not exceeding 10 % of rice by weight)
Not exceeding 70%
Japanese liquor junmaishu (sake made without added alcohol or sugar)
Not exceeding 70%
Japanese liquor special honjozoshu
Not exceeding 60%
Japanese liquor special junmaishu
Not exceeding 60%
Japanese sake ginjoshu
Less than 60%
Japanese liquor Daiginjoshu (Super high-quality sake brewed from rice grains polished to 50 percent weight or less)
Not exceeding 50%

However, the official regulation on the rice-polishing ratio for junmaishu was abolished on January 1, 2005.

Regarding this abolishment, many experts are concerned that, even if cost reduction is attempted by brewing junmaishu with the rice-polishing ratio of about 75% which is almost equal to that of futsushu, the consumers who do not find the difference of the taste gladly choose less expensive sake, which will lead to lowering sake brewing technologies and quality, resulting in further contribution to worsening the period of sluggish consumption of Japanese sake. On the other hand, sake with a low rice-polishing ratio brewed from rice grains featuring a rice-polishing ratio of about 80%, which is rare even for futsushu, has appeared. Some people welcome that traditional Japanese sake produced before the mechanization of rice polishing can be now called junmaishu (sake made without added alcohol or sugar). For detail, refer to Japanese liquor junmaishu.

Furthermore, the the rice-polishing ratios of rice for sake brewing are grouped into the following three categories.

Rice-polishing ratio by weight
The rice-polishing ratio by weight is a method to measure the rice-polishing ratio based on weight.

For example, if the brown (unpolished) rice of which weight is 100kg is polished to 85kg, then the rice-polishing ratio of the polished rice by weight is 85%.

Apparent rice-polishing ratio
Apparent rice-polishing ratio is rough rice-polishing ratio and usually means the rice-polishing ratio by weight.

In case of rice-polishing ratio by weight, the weight of the whole polished rice grains decreases in proportion to the rice-polishing ratio, but some grains are not much shaved and others are shaved to the level of sake rice structure. And, as a result, the degree of polishing individual grains varies but the rice-polishing ratio as the apparent value is obtained by averaging the polishing-ratios of all the rice grains. This is the apparent rice-polishing ratio.

However, when it comes to Japanese liquor ginjoshu, as the polishing degrees of individual grains tend to affect the quality of the sake as a whole, higher accuracy in polishing data is required, and then the notion of shin seimai buai (true rice-polishing ratio) was fformed.
(Refer to the section ' Vertical-type rice-milling machine'.)

Shin seimai buai (true rice-polishing ratio)
Shin seimai buai is the rice-polishing ratio which is of higher precision than the apparent rice-polishing ratio and closer to the true states of the polished grains and is defined by the following formula.

Senryuju (weight of 1,000 rice grains) is the weight of extracted 1,000 rice grains measured in the unit of gram. That is that the rice-polishing ratio of every 1,000 grains is closely measured. This is essential for brewing high-quality sake.