Semaibuai: Rice Polishing
One of the key elements in determining the flavour profile of a sake is the amount to which the rice grain has been milled down. A grain of rice consists of 5 main layers.
Seed Coat
Nucellus
Aleurone Layer
Subaleurone
Starchy Endosperm
Outside of extremely rare cases that make use of unpolished rice, known as genmaishu, only the starchy endosperm is used in sake.
A brief history of semaibuai
Rice polishing has been practiced in Japan since ancient times, using a mortar and pestle. In the 17th and 18th century, water-powered mechanical pestles appeared. However, the process was still time consuming and labour-intensive, making white rice a luxury good until the second half of the 19th century, when technology had improved enough to make it affordable for everyday people.
In the 1930s, a vertical polisher was invented that allowed the creation of the fine rice used in modern sake production for the first time. However, even today these machines are incredibly expensive, and all but the biggest sake breweries outsource the job to specialised companies.
The polishing process
|
Semaibuai
|
Hours Required
|
|---|---|
|
70%
|
12
|
|
60%
|
33(Standard Junmai)
|
|
35%
|
63
|
For semaibuai, the rice kernel goes through a process of being ground by a rotating millstone. The rice flour produced by polishing the rice is removed, and the process is repeated. To achieve the desired polishing rate, this process must be repeated many times, especially for more finely milled sake.
Why is a more polished sake more expensive?
As the rice kernels become smaller and smaller, they become more delicate and prone to breakage. In order to prevent this, this rotation speed of the millstones must be lowered, exponentially increasing the required time to create a finished product. The number of times a kernel must be fed through machine is also far greater for highly polished sake.
Why Polish?
Polishing sake removes the outer proteins, minerals, and lipids from a rice kernel.
- (Colour) Removing the minerals, particularly iron, prevents browning.
- (Aroma)The reduction of lipids allows for the development of aromatic esters, the main source of the “fruity” flavours often found in high-quality nihonshu
- (Structure)Removing the proteins helps to prevent age deterioration, and prevents excessive bitterness.