超扁平精米
Super-flat Rice Polishing

Super-flat Rice Polishing

A unique rice polishing technique that polishes away the same thickness from each surface of the brown rice. It removes the proteins concentrated near the surface of the rice to a level and with an efficiency never seen before, while the required starch remains.

Why sake brewing requires
rice polishing

The rice germ and outer husk contain large amounts of proteins, oils, minerals and vitamins. These compounds change the balance of the fermentation by accelerating the growth of koji mold and yeast. They also degrade the quality of the sake by causing tinting and unwanted flavors. The purpose of the rice polishing process is to remove such elements. But it is not a matter simply of “the more polishing the better.” A high degree of polishing results in a delicately-flavored sake such as daiginjo. A medium degree of polishing will result in a sake such as junmai, which has a robust richness that makes it perfect for drinking warm. So variations in rice polishing translate into a rich variety of sake types, and polishing is a vital factor in the final flavor.

Problems with conventional
rice polishing techniques

The most widespread polishing method seeks to polish rice as quickly as possible by increasing the rotational speed of the rice-polishing machine roller (whetstone). At the same time the density of rice in the polishing chamber is lowered to prevent cracks and splits. This makes the grains far more likely to rotate wildly on their short axis, leading to more polishing action being applied to the ends of the long axis of a grain. This results in spherical grains.

As a result, the rice is polished to an extreme degree at the ends of its long axis, while the shorter, stouter axis is barely touched. The outcome is that the conventional polishing technique leaves behind undesirable elements on the short axis, and wastes precious starch on the long axis. (See chart on rightbelow)

Conventional polished rice (spherical polished rice)

The solution: flat rice polishing

As a way to overcome these defects, Tomio Saito and others proposed the flat rice polishing technique. This method aims to polish away the same thickness from each surface, resulting in a flatter rice than with previous methods.

It is clear from the diagram on the rightbelow that unwanted parts are completely removed while the required starch remains.
(For this method Mr Tomio Saito received the “Award of Merit” of the Brewing Society of Japan.)

Super-flat Rice Polishing

The principle of the flat rice polishing technique can be seen in the animation below. With slow rotation of the rice-polishing machine roller (whetstone), and a high density of rice in the polishing chamber, the rice will rotate on its longer axis, resulting in long, thin grains.
However this method requires much more time to polish rice than the conventional method, and presents a far greater risk of cracked grains.

A simple benchmark:
the flat rice polishing ratio

So what is a rice polishing ratio? The equation “weight of polished rice divided by weight of unpolished rice times 100 (%)” only gives the percentage of polished rice yielded from unpolished rice and, at the same time, the percentage of unpolished rice discarded as bran. It does not tell us how efficient the rice polishing has been.
We recommend a new approach: adopt as benchmark the removal of unwanted elements from a rice grain’s thickness along the short axis, which is the hardest part to polish by traditional methods. This gives us the flat rice polishing ratio.

Flat rice polishing ratio (%) = (Thickness of polished rice/Thickness of unpolished rice)³ x 100

The easiest part of a rice grain to polish is its length, then its width and, finally, polishing the thick part in the middle is the most difficult. So if a calculation of volume can be made based on how much of the thickness – the most difficult part to polish – has been removed, it is possible to estimate that a greater amount of unwanted material has been polished from the length and width. It would therefore have to be considered equal or superior to rice polished to the same ratio in the shape of the grain.

Daishichi’s super-flat rice
polishing technique

Daishichi has always been very interested in the flat rice polishing theory proposed by Tomio Saito and has worked hard to implement it in practice. In order to make the benefits of flat rice polishing clear, and to overcome the challenges this method has encountered – cracked grains, as well as the extra time and labor the process requires – Daishichi has performed innumerable polishing tests, ultimately succeeding in establishing the most efficient flat rice polishing technique to date. As it surpassed the assumptions of its inventor, Mr Tomio Saito, we have named our polishing technique “super-flat rice polishing.”

Super-flat rice
polishing technique
Conventional rice
polishing techniques

In the case of conventional rice polishing, at whatever polishing ratio, the apparent polishing ratio normally is smaller than the flat polishing ratio. But because the grains become spherical, the stouter part is not sufficiently polished. As a result, the bran is not removed as much as the polishing seems to show.

In contrast, in the case of Daishichi’s super-flat rice polishing, with a flat rice polishing ratio of 51.3% when the apparent rice polishing ratio is 70%, the quality is overwhelmingly better. It is also possible to reach a flat polishing ratio of 34% with an apparent polishing ratio of 51% (in the case of conventional polishing the result is much worse, as the flat polishing ratio becomes 64.4% at an apparent polishing ratio of 35%).

Apparent rice
polishing rato
Flat rice
polishing raito
Unpolished rice  
90 71.5
80 64.1
75 53.7
70 51.3
63 44.4
58 36.8
51 34.0
Apparent rice polishing raito and flat rice polishing raito
in the case of Daishichi's superlfat rice polishing.

Quality of completed rice

A comparison of analyses of super-flat polished rice and conventionally polished rice demonstrates that super-flat rice polishing is extremely efficient at removing the large amount of proteins near the surface of rice grains, and that it is an enormously effective polishing method. 70% super-flat-polished rice (apparent polishing ratio) and 58% conventionally-polished rice (apparent polishing ratio) contain the same amount of remaining protein. This means that simply using the super-flat polishing method achieves the same result as improving the conventional polishing ratio by 12%.

Graph of polishing method and protein
Sample Flat rice
polishing raito
Shape Residual crude protein
Competitor
35%
Yamada Nishiki
64.4% Spherical 51.55%
Daishichi
58%
Gohyaku Mangoku
36.8% Super-flat 44.07%
Daishichi
51%
Yamada Nishiki
34.0% Super-flat 44.32%
Table of Comparison with conventional daiginjo rice.

Quality of completed sake

An actual brewing test was performed by making sake with rice of the same apparent polishing ratio, polished by both the super-flat technique and the conventional method. The rice polished with the super-flat technique resulted in a beautiful, clean-tasting ginjo sake, low in amino acids. This is also clearly reflected in the tasting results. On a 4-point assessment, with 1 being the highest rating, sake made from conventionally polished rice received an average of 2.45, while super-flat polished rice-derived sake received a 1.65.(This is the average of the points given by each judge, with 1: very good, 2: good, 3: average, 4: problematic. The lower the average, the better)Also, when the test samples were deliberately exposed to sunlight, then tasted, the sake made from super-flat-polished rice had barely a hint of “light-struck flavor” degradation, revealing a substantial preservation margin compared to sake made from conventionally polished rice.

Graph of comparison of amino acidity

Thoughts on recent extreme polishing ratios

The conventional polishing method that results in spherical grains is inefficient. Even if these spherical grains are made extremely small, can they reach the same quality as rice polished with the super-flat method?

No, we don’t think so. Our way of thinking about rice is different.
Daishichi has a preference for good sake rice (shuzo kotekimai), which has a white, opaque, soft center, the so-called “white heart” (shinpaku). This shinpaku is responsible for the beautiful, soft umami of the sake. But as the shinpaku has a soft and fragile structure, the grain will break when the rice polishing reaches this part. Daishichi’s super-flat rice polishing technique takes great care not to break the shinpaku and skillfully makes use of it.
But the fragile shinpaku forms an obstacle when polishing the rice to an extremely small size. Ironically, it is more convenient therefore to use rice without shinpaku.
Daishichi’s philosophy is to have the highest respect for the rice and to bring out all its qualities. It is not possible to obtain the supreme enjoyment of umami by extreme polishing.

Daishichi’s rice polishing ratio is a basic super-flat polishing ratio of 50% even in the case of our highest class sakes. We are convinced that rice of a pure and superb quality is obtained by that method, and not by making the rice as small as possible.