Daishichi Sake Brewery has long been very interested in the flat rice polishing method and upholds a firm commitment to its implementation. In order to make the benefits of flat rice polishing clear, and to overcome the challenges this method has encountered - the extra time and labour the process requires - Daishichi has performed innumerable polishing tests, ultimately succeeding in establishing the most efficient flat rice polishing technique to date. We have named this polishing technique "super-flat rice polishing".
Super-flat rice polishing developed by Daishichi Sake Brewery
By prioritising the polishing of the flatter, thicker portions of the grain that have the largest surface area, the total amount of unwanted material remaining is minimised.
Polishing results
Chart 1 Apparent rice polishing ratio and flat rice polishing ratio
|
Apparent rice polishing ratio (%) |
Flat rice polishing ratio (%) |
| Unpolished rice |
|
| 90 |
71.5 |
| 80 |
64.1 |
| 75 |
53.7 |
| 70 |
51.3 |
| 63 |
44.4 |
| 58 |
36.8 |
|
Chart 2 Assessment of polished rice
|
Rice germ (%) |
0.0 |
|
Flawed rice (%) |
1.0 |
|
Ratio of unusable rice (%) |
3.1 |
|
Quality of completed rice
|
Polishing method and crude protein content
|
A comparison of analyses of flat polished rice and conventionally polished rice demonstrates that flat rice polishing is extremely efficient at removing the large amount of proteins on the surface of rice grains, and that it is an enormously effective polishing method. 70% 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 flat polishing on rice achieves the same result as improving the conventional polishing ratio by 12%.
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Flat rice polishing produces grains with a large amount of glucose and few amino acids. (See Chart 3.) This is a very welcome result because amino acids cause blurred flavour and glucose content is crucial to the production of the ginjo flavour. B
It is clear that flat rice polishing not only increases the utilisation ratio of the raw ingredients, but is also particularly suited to the manufacture of high-quality sake.
Chart 3: Testing of polished rice consumption
| @ |
Conventional rice polishing |
Flat rice polishing |
| Degrees Baume |
6.6 |
6.6 |
| Degrees Brix RDS (%) |
10.8 |
10.8 |
| Glucose (%) |
4.01 |
4.21 |
| pH |
6.03 |
6.03 |
| Amino acid acidity |
0.50 |
0.45 |
|
Samples of each variety of Daishichi polished rice were compared with traditional daiginjo rice: a 35% polished sample of Yamada Nishiki from a competitor that would be considered a good rice by traditional standards.
Chart 4 shows how much material has actually been removed from the grain by using the flat rice polishing ratio for each sample. For the ginjo rice samples, it also shows the amount of residual crude protein*. This indicates how much unwanted material remains after the polishing process.
(*) The residual crude protein is calculated by measuring the amount of crude protein in the unpolished rice, and the amount remaining after polishing.
Chart 4 A comparison with traditional Daiginjo rice
|
Sample |
Flat rice
polishing ratio
|
Shape |
Residual crude protein |
|
Competitor 35
Yamada Nishiki |
64.4 |
Traditional |
51.55 |
|
Competitor 34
Yamada Nishiki |
60.1 |
Traditional |
@ |
|
Competitor 33
Yamada Nishiki |
59.7 |
Traditional |
@ |
|
Daishichi 65
Hanafubuki |
50.3 |
Super-flat |
@ |
|
Daishichi 58
Gohyaku Mangoku |
36.8 |
Super-flat |
44.07 |
|
Daishichi 51
Yamada Nishiki |
34.0 |
Super-flat |
44.32 |
|
Daishichi 38
Yamada Nishiki |
46.5 |
Somewhat flat |
48.31 |
All of our polished rice ratios are superior: 65%, 58%, 51% and 38%. Our method achieves better results than the conventionally-milled 35%, when measured as a flat rice polishing ratio. The amount of residual unwanted matter is also far lower in our 58% and 51% polished rice than in the traditionally-milled 35% sample. It is clear from the above results that Daishichi's super-flat rice polishing method is extremely effective.
Quality of completed sake
When actual brewing tests were performed and real sake was made, the result was a beautiful, refined drink, low in amino acids. Flat rice polishing has now made it possible to create a clean-tasting ginjo-type of refined sake without wasting the rice that is the main ingredient.
 |
From the fact that amino acidity in flat polished rice is obviously far lower than that in conventionally polished rice, it is clear that flat polishing removes proteins efficiently, and this is reflected in the finished sake.
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 flat polished rice-derived sake received a 1.65. The examiners also submitted a short appraisal. The flat-polished rice sake was described as having a ginjo bouquet, as well as being smooth and rounded, clean-tasting and refined.
Also, when the test samples were deliberately exposed to sunlight, then tasted, the flat-polished rice alcohol had barely a hint of "light-struck"@flavour degradation, revealing a substantial preservation margin compared to conventionally-polished rice brews.
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Graph 5 Analysis of sake brewed for experimental use
| @ |
Normal polished rice |
Flat-polished rice |
| A |
B |
C |
D |
| Alcohol volume (%) |
18.1 |
18.5 |
17.7 |
18.1 |
| Nihonshu-do |
+1 |
+1 |
+1 |
+1 |
| Acidity |
2.0 |
1.8 |
2.0 |
1.8 |
| Amino acid acidity |
1.05 |
1.05 |
0.75 |
0.80 |
| Total nitrogen (%) |
0.064 |
0.065 |
0.056 |
0.053 |
| UV region absorption |
7.472 |
7.438 |
6.589 |
6.440 |
| 65 C pasteurisation
colouring
|
0.076 |
0.073 |
0.066 |
0.068 |
| Tasting rating |
2.4 |
2.5 |
1.3 |
2.0 |
Conclusion
In the world of daiginjo sake, the focus until now was on ever-lower polishing ratios. When assessing the quality of the rice, the only issues raised were the reduction of the flawed-grain ratio through removing rice germ, grooves and flawed grains. The spherical shape was basically taken for granted.
However, as this research has shown, lowering the polishing ratio but keeping the spherical shape is not enough to remove unwanted material. It is clear that rather than lowering the polishing ratio, reducing the flat rice polishing ratio is the key.
The super-flat rice polishing technique can reduce flat rice polishing ratios to an extraordinary degree, thus opening the path to the production of high-quality refined sake that far surpasses its predecessors. This technology is also an environmental pacesetter. The needless waste of raw rice is prevented, so it is possible to produce large returns with a smaller amount of polishing than would previously have been required.
Documentation
1) Tomio Saito, Nobuya Tezuka, Osamu Kondo, Koji Okada, Yasuteru Sakamoto, Katsuro Kubo, Ryuichi Sugiyama, Naotaka Kuribayashi, Miyoshi Kato, Tadashi Yoshii: Agric. Biol. Chem, 89, (6) 489 (1994)
2) Tomio Saito, Minoru Kinoshita, Yuko Takayasu, Tameharu Suwa, Yoko Kubota: Agric. Biol. Chem, 88, (1) 69 (1993)
3) Masaru Ohashi, Tameharu Suwa: Agric. Biol. Chem, 76, (7) 436 (1981)
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