Last March, we were in the Kochi region to visit several producers, and had the opportunity to visit Kuyohiko Takeuchi's rice polishing unit. It was a very interesting moment that we wanted to share with you, as a plunge into the heart of the most preliminary and decisive stage in sake-making. The “seimai” not only determines the category to which the sake belongs, but also greatly influences its taste characteristics.
The interior of a polishing unit

A modern polishing unit is a place where you'll find different zones: one for receiving and storing rice from the latest harvests. It is packed in 50 kg bags. A polishing area with a series of large silos. These are the machines used for polishing. A sorting and packaging area, and finally, an area where the polished rice is stored prior to shipment to the various sake breweries.

But before arriving at such a structure, it should be remembered that the history of polishing really began in the 7th century with the appearance in Japan of a waterwheel technique imported from Korea. Then, during the Edo period (1603-1868), the emergence of a certain sense of refinement in Japanese society and the search for more elegant products led to significant development of this practice. Numerous breweries were set up at this time, and producers began to include polishing as an integral part of the sake-making process, the idea being to pay greater attention to quality. Over time, techniques were perfected, and it was only in the twentieth century that improved machinery enabled the highly advanced polishing now synonymous with top-of-the-range sake.


Old rice polishing machine

The benefits of polishing are linked to the structure of the grain. The strains of rice used to make sake are different from those used for everyday consumption. Sake rice grains are larger, richer in starch and, in most cases, have a “shinpaku”, a soft, white, opaque central inclusion. In this dense core, the conversion of starch into simple sugars by koji enzymes is favored, making the rice easier to liquefy.Sake rice after polishing

But shinpaku is the visible part of this heterogeneity, while the outer layers are rich in many other elements such as proteins, amino acids, lipids, fatty acids, vitamins and minerals. The presence or absence of these elements will considerably influence the efficiency of the yeasts in the fermentation process and, ultimately, the taste characteristics of the sake.

To understand the general principle of polishing, let's go back to ancient times. Traditionally, polishing was carried out using wheeled machines or a mortar and pestle system - rudimentary, time-consuming and often destructive methods for the grains. At the end of the 19th century, the first Satake machine saw the light of day, achieving a record polishing rate of 75%. In the 1930s, the first vertical polishing machines appeared, offering even more advanced capabilities. However, few kura can afford to invest in such expensive machines, which is why they generally turn to specialized service providers.Different types of rice, depending on the degree of polishing

The operation of a modern machine is based on a fairly simple principle. The rice is fed into the polisher, inside which a hydraulic wheel turns on itself to precisely dose the quantity of grains to be sent into the polishing chamber. Polishing then takes place between a rotating grinding wheel and a fixed cage. During this process, the grain heats up and loses some of its moisture, making it more brittle. As it loses its outer layers, the grain becomes increasingly brittle, requiring a gradual reduction in rotation speed to preserve its integrity. This phenomenon explains why it takes over 60 hours to achieve a polishing rate of 35%.

At the end of each cycle, the grains exit via the same wheel they entered, and a new cycle can be started if necessary. Meanwhile, the polished rice powder is discharged through a sieve. This component is called “nuka” (see box).

The polishing rate, otherwise known as “semaïbuaï”, is a value that expresses the percentage of rice remaining in relation to the initial grain (considered as “100%”). It is determined by subtracting the input weight from the output weight. Notable values for semaibuai are 70%, the minimum for Honjozo, 60% for ginjo and 50% for Daïginjo. (In the past, rice used for junmai production also had to be 70% polished, but this has not been mandatory since 2004).
And since extremes are always fascinating in this context, let's mention Kameman Genmaïshu sake, which is produced with Genmaï rice, i.e. not polished at all, and at the opposite extreme, Tatenokawa's Komyo sake, which is produced with 1% polished rice!

Different levels of rice polishing

There are different technical variants for polishing, with more or less complex methods chosen according to the wishes of the sake producer. These include:

Centrifugal polishing, which uses rotating force to abrade the grains more evenly and gently than traditional methods. This technique reduces breakage, limits heat and preserves the shimpaku. Longer but more precise, it enables extreme polishing rates to be achieved.

Soft Milling progressively reduces the outer layer of the rice by applying less pressure and friction than conventional methods. Slower but more precise, it limits heat and breakage, better preserving the grain's starch.

Asymmetrical polishing removes the rice bran in an irregular pattern, preserving more of the starchy core while reducing unnecessary losses. Unlike conventional polishing, it specifically targets certain areas of the grain, optimizing fermentation.

Henpei Seimai, literally “flat polishing”. This is another selective polishing method that involves removing the outer layers of the grain unevenly, so that some parts of the rice are polished more finely than others. This allows certain starch-rich areas of the grain to be retained, while eliminating the heavier, less desirable parts. Genkei Seimai, a variant of the previous and the most recent technique, involves polishing the rice to its original shape (Genkei = same shape).


Rice polishing is now carried out by modern machines whose engineering is remarkably sophisticated. They combine precision and efficiency, a field in which the Japanese excel. We were lucky enough to see a Satake machine coupled with a laser sorter at work. Not only is the rice polished with ultimate precision, it is also sorted with phenomenal efficiency as it leaves the column, before being packed.

Satake machine for polishing and sorting rice

It's fascinating to watch the grains pass at phenomenal speed through an oblique plate traversed by a laser beam that instantly detects and removes the slightest grain carrying an imperfection.

During tastings and discussions, we like to point out that it would be a shame to reduce the quality of a sake to the degree of polishing of the rice used in its production. It's important to explore, taste and savor all the diversity and nuances this beverage has to offer, without limiting oneself to one category.
Nuka is the residue of the polishing stage, a fine starch powder, an ultapure rice flour with interesting properties and surprising applications. Indeed, nuka is increasingly used in the high-end cosmetics industry, where it is prized for its gentle, moisturizing properties. Rice starch is particularly appreciated in skin care, integrated into products such as powders, creams and masks, thanks to its silky texture and soothing properties. It is said in the sake world that Toji are the people with the softest hands in the world!