Once harvested, in early autumn, the rice is cleared of the brown cuticle surrounding it, and then goes into sake production. But the grain is not used as it is, and an important step will take place, polishing. Called seimai in Japanese, it consists of circulating the rice in large vertical grindstones. The grains will wear against the stone and the outer layers will be nibbled and reduced to a fine powder. The diameter of the grain gradually reduces to leave only a small white pearl at the end of the process.  

The interest of polishing is explained by the inhomogeneous distribution of the elements that make up rice. Rice contains starch, fatty acids, proteins and amino acids, which are distributed in such a way that the further you go towards the heart of the grain, the higher the concentration of starch. The outer layers are rich in all the other compounds. Polishing the rice grain therefore concentrates the starch. This operation has a significant impact on the taste of the sake, because by getting rid of the outer layers, you get rid of the compounds that can bring additional flavors, and you will naturally tend to make a fine, elegant sake. On the other hand, keeping matter, proteins, fatty acids and amino acids, by polishing the grain less, will bring character and power to sake. (It should be noted here that the rice used for sake production is grown especially for this purpose and is quite different from ordinary rice, which is larger, richer in starch, and above all very resilient).
The degree of polish of the rice, or seimai buaï in Japanese, is a factor clearly indicated for each sake. It is always expressed as a "percentage of matter remaining". For example, the label on a bottle with a 60% seimai buaï indicates that 60% of the rice in the bottle has been polished. In other words, the rice used to make this sake weighs 60% of its original weight. This value is technically determined by weighing the rice before and after polishing. Two main levels of polishing are clearly distinguished in the usual classification of sake (Tokutei Meisho Shu classification): 60%: the sake is called "ginjo", the rice is polished to at least 60%, 50%; it is a sake called "daïginjo". In Japanese, "daï" means "great", so it is the superior evolution of ginjo with a minimum polish of 50%. The grain can be polished to the extreme, to values bordering on the commercial argument or, conversely and very rarely, used raw, without any polishing, the rice is then called genmai.

le riz complet puis poli avant la production de saké
From a purely technical point of view, as briefly discussed above, polishing requires passing the rice through vertical grinding wheels. These are relatively expensive and are not available in all breweries, and many small businesses buy the already polished rice from the producer. They order in advance the type of rice they want, carefully indicating the degree of polishing. Seimai, despite its apparent simplicity, remains a crucial step in the preparation of sake. Its control must be perfect. It must not be too fast in order to prevent the grain from heating up due to friction, which would cause it to cook or break, affecting the taste of the sake. In the end, the grain of rice should look like a round pearl. The "shinpaku", which means "white heart" in Japanese, is the white, opaque part that can be seen through the transparency of an intact grain of rice. Very round... except for a few exceptions... because there are interesting alternatives to classic concentric polishing. For example, modern machines can be used to polish the rice grain longitudinally, giving it the appearance of a miniature rice grain at the end of the process. This method is called "henpei seimaï" and allows excellent results to be obtained with very refined sake for a lower degree of polishing. The use of rice is optimized and costs are better controlled.
The residual product of this polishing step is a very fine white powder, which is relatively close to conventional rice flour. However, in contrast to conventional rice flour, which comes from the processing of rice for consumption ( about 92% is polished), the quality of the rice powder from sake production is outstanding. Rather than being processed into aperitif cookies or mochis (a kind of rice cake), this fine powder is used specifically for the production of premium cosmetics.

machine à polir le riz à saké

The parameter of rice polishing is certainly the one that attracts the most attention for people who start discovering sake, often with the shortcut of saying that "the more polished the rice, the better the sake. But relying solely on the degree of polish to express the quality of a sake would be simplistic, as this factor should be considered in a much broader context. One must not forget to take into account the name of the producer, the size of the factory, the yeasts used, the quality of the water, etc... Also, referring only to this percentage to guide the choice of a bottle would considerably restrict one's experience of sake and deprive the taster of countless moments of pleasure, starting with the discovery of rich, powerful and rustic sake, as some junmai can be. Choosing a sake is ultimately a matter of timing and mood, delicacy or rusticity... the ideal is of course to vary the pleasures!