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Super-flat rice polishing techniques promise a bright future for ginjo sake
Super-flat rice polishing

The solution: flat rice polishing

Flat polished rice
Flat polished rice (evenly polished rice)

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 left that unwanted parts are completely removed while the required starch remains.

The principle of the flat rice polishing technique can be seen in the animation on the left. 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.

The principles behind flat rice polishing
The lower the rotational speed of the rice-polishing machine roller (whetstone), and the higher the density of rice in the polishing chamber, the more likely it is that the grains will rotate on the longer axis, resulting in long, thin grains.

As we explain in The solution: flat rice polishing, the Daishichi Sake Brewery found a solution to this problem by improving the effects of flat rice polishing, following research into ways to push the degree of flatness one step further.

A new 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 cannot tell us how efficient the rice polishing has been.

We recommend a new approach: adopt as a 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

What do flat rice polishing ratios tell us?
The easiest part of a rice grain to polish is its length, then its width and finally, polishing its thickness 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. This means that rice polished to this ratio will automatically be of higher quality than rice polished to the same ratio calculated by the conventional polished rice equation.

[Diagram A]

Even if conventionally polished rice has a polishing ratio (pound for pound) of 35%, if the rice has been polished to a spherical shape, it would correspond to a flat rice polishing ratio of 50%. It would therefore have to be considered equal or superior to grain-shaped polished rice at a rice polishing ratio of 50%. [See Diagram A]

[Diagram B]

On the other hand, take polished rice with a rice polishing ratio (pound for pound) of 50%. If that rice is flat-polished (rather than spherical), it would have a 35% flat rice polishing ratio. You could expect the same quality from this flat polished rice that you would get from grain-shaped polished rice at a polishing ratio of 35%. [See Diagram B]



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