Closeup of Sake Production: Rice Polishing

Greetings Sake Lovers, welcome to another KURAND Magazine article that introduces you to the world of sake.

The flavors and aromas of sake are so subtle, that on first sip, the boundaries between one sake and another can seem just as vague. But with continued tasting, you may start to notice that some sake are more elegant than others, more silky and the texture more delicate. There are many reasons for this, but one of the biggest is rice polishing, seimai in Japanese. It is one of the first stages of the sake production process. In this article, we take an in-depth look at it.

Sake Production in a Nutshell

A very basic diagram of the sake brewing flow can be found in the chart above. This is just a very basic outline. The process varies depending on the variety of rice and the target style of sake. Seimai-buai plays a pivotal role in determining the end style and flavor, so it definitely deserves to be explained in more detail.

A Closer Look at Rice Polishing


Whether for eating or brewing with, rice comes in two forms: genmai (brown rice) and hakumai (white rice). Hakumai is basically genmai after the outer layer of rice bran has been removed. In brewing, we refer to the removal process as polishing or seimai in Japanese.

The portion leftover after polishing is called the rice polishing ratio or seimai buai in Japanese.

For table rice, polishing stops at the 80% mark. But for sake brewing, depending on the desired style, polishing may extend beyond the outer edges of the grain all the way to the core of the kernel.

Brewing Rice

Although it is possible to make sake with table rice, this is not desirable because it contains so much protein which can produce off flavors in the end product, so for premium types of sake, it is more common to use rice cultivated specifically for brewing called shuzokotekimai (literally, brewing rice). See these past articles for more information.

Perhaps the biggest difference between table rice and sake brewing rice is the size and position of something called the shimpaku (literally, white heart). This is basically a nucleus filled with starch. And of course, in brewing, the brewer needs starch more than they do protein. In eating rice, the shimpaku is normally found near the germ of the rice, which means it is polished away in the polishing process. However, in brewing rice, it is found just off-centre, so the brewer is able to polish around it. This is by far the biggest reason that brewing rice is more suitable for brewing.
Characteristics of Brewing Rice

■Exterior:Larger grains. Size is important because smaller grains are unable to withstand the heat and friction produced during polishing, especially higher levels of polishing.

■Shimpaku:Shimpaku has a low protein content and has high viscosity making it more durable when being polished. It also dissolves better in the moromi (fermentation mash). Brewing rice has a higher ratio of shimpaku than eating rice.

The History of Rice Polishing


Early rice polishing was done using a kiusu (wooden mortar) (also called kometsuki).
During the beginning of the Edo period, in order to polish more efficiently a ishiusu (stone mortar) was used. The second shogun Hidetada Tokugawa then imported an ashibumi-karausu (foot Chinese millstone) from China.

Until the late 18th century, it was only possible to polishing up to 23kg of rice in one day. In later years, high performance water mills increased efficiency by an extra 1kg. However it was still difficult and impractical to pbolish down to less than 80% of the grain.

Then, in 1986, the revolution arrived, in the form of the world’s first polishing machine. The polishing machines used today were built in 1930. Until this point upper limit for polishing was 70%. It may surprise you to learn than brewers only just recently gained the technology to polish beyond that and that polishing even entered into the brewing equation at all.

How Does Polishing Change Sake?


So why polish in the first place? Well, there are many reasons but above all, it is all about style, and, although less the case nowadays, quality. As well as starch, brewing rice contain vitamins, proteins, and fats. If there is an excess of these in the final fermentation, the yeast will ferment too rigorously and may produce zatsumi (off flavors). In addition to zatsumi, the balance of the sake may be lost. By removing these less desirable components, brewers can produce more delicate, smooth styles of sake.

Rice Polishing and Sake Grades

With advancements in brewing, the focus has begun to shift from rice polishing, but you still can’t talk about sake without talking about the polishing ratio, not least because it is the main guideline which the law uses to grade sake.

Below are the grades of sake and the minimum polishing ratio that the brewer must achieve to quality for them. Note, as long as brewers meet these minimum guidelines, they are allowed to polish in excess to provide the customer with more quality.

Grades Rice Polishing Ratio
Junmaishu No polishing guidelines
Honjozoshu 70% or less
Tokubetsu Junmaishu 60% or Less
Tokubetsu Honjozoshu 60% or less
Ginjoshu 60% or less
Junmai Ginjoshu 60% or less
Daiginjoshu 50% or less
Junmai Daiginjoshu 50% or less

How Difficult is Polishing? The Brewers Explain

Even though, thanks to machines, polishing is an easier task than it once was, it still requires a degree of skill. Many breweries actually outsource the job. But there are some breweries that pride themselves in doing it in house.

We asked some of them to share their experience about polishing with KURAND.

Q. Have you ever experienced any problems with polishing? (or have you heard any stories from other brewers)

I believe that, even today, polishing rice is a difficult task. A buzzword is trending in the industry now is shin-seimai-buai (true ratio, indicating the quantity of polished rice gained from a given quantity of brown rice). This means that, a 1 ton of genmai polished down to 600kg will have a ratio of 60%. However, this does not mean that the rice grains are evenly polished. Even with all the care in the world, some grains of rice will still break during the process. If you eliminate these broken rice grains, and you still have 600kg remaining, each rice grain must in fact be larger than 60% of the original size. In other words, the actual ratio is closer to 62-63%. This is the shin-seimai-buai. The smaller the difference between seimai-buai and shin-seimai-buai are, the better the quality of seimai. However, this becomes more of a challenge for the higher polishing ratios.
(Kikunotsukasa from Shuzo・Mr.Hirai)

It is difficult to achieve the same polishing ratio for higher polishing. And soft rice breaks very easily.

(Mr.Takizawa from Takizawa Shuzo)

—— the smaller it gets the easier it is for it to break. Some rice are inherently suited for polishing to high levels and some are not.

Even today, polishing is still a challenge. And that is why, even today, this consideration of the difficulty and the cost of the extra volume of rice that is needed still determines the end price. However, just because a lot is polished off does not mean it will make a good quality sake. There are so many other parts of the process and ingredients that play a role in determining quality and as every brewer brews with the same sweat and tears, every sake is high quality. It is more about style and whether that matches your preference. Preferences vary from person to person. And, more importantly, different styles of sake match different foods, different glassware and different situations and seasons. Please do not restrict your drinking to a particular polishing ratio and try everything that the sake world has to offer. That is our number one wish as a brewer.

So there you have it, polishing does not necessarily produce a better sake, it’s a question of preference and a myriad of other factors in the brewing process. And remember, every sake is made with the same amount of sweat and tears, hopefully not too many tears.

All that is left for us to say is to come to KURAND, and try the vast selection of different sake styles that we offer. And with a variety of all-you-can-taste packages to suit a range of budgets, there is no better way to discover sake.

We look forward to welcoming you very soon!