Sake Guide Lesson 3: What Is Rice Polishing Ratio?

Each step in the sake-brewing process is critical to sake production, but rice polishing in particular garners a lot of attention due to its influence on sake categorization and pricing. Rice polishing is the process by which the outer layers of a grain of rice (the bran) are polished or milled away. Here, we discuss the purpose of rice polishing, how it’s done, and its effects on the categorization and flavor profiles of sake.

Purpose of rice polishing

Simply put, “seimaibuai” (rice polishing ratio) is a description of the percentage of grain that remains after a part of the rice has been polished away. For example, sake with 60% RPR means that about 40% of the rice’s outer layer has been milled away. You can usually find a sake’s rice polishing percentage on its label.

Rice polishing illustration

Why is rice polishing necessary? Rice polishing shaves away protein and fat, leaving the starchy interior (“shimpaku”) used in saccharification (the conversion of starch to sugar), which is necessary to brew alcohol. Brewers determine the level of rice polishing and gently mill away these elements to achieve the desired taste profile of the final product.

Rice polishing ration illustration 2

Rice polishing helps to manage the protein and fat that affect the brewing process and flavors of sake.

These days, breweries use vertical rice polishing machines that are very precise and automated; these machines are a far cry from the traditional methods of long ago!

Rice polishing machine

Vertical rice polishing machine

Higher rice polishing ratio indicates that a greater percentage of the original rice grain remains after polishing. This type of sake typically boasts rich umami from the rice and fuller body. On the other hand, lower rice polishing ratio represents sake brewed with more milled rice, which often results in cleaner and fruitier taste notes. Many brewers make products with different rice polishing ratios under the same brand to cater to different preferences and occasions.

samples of Yamadanishiki rice

Samples of Yamadanishiki rice used by Dassai. Left: brown rice. Right: 77% of the rice is milled away (23% rice polishing ratio). Bottom: 61% of the rice is milled away (39% rice polishing ratio).

Categorization of sake

Rice polishing ratio and brewing method are factors in determining the sake category. Another factor is the ratio of ingredients, like koji and brewer’s alcohol (if added). When it comes to premium sake (“tokutei meishoshu”), there is only one category that does not have a set RPR: junmai. Aside from that, the RPR for honjozo sake must be at least 70%; tokubetsu (“special”) honjozo, tokubetsu junmai, junmai ginjo and ginjo at least 60%; and junmai daiginjo and daiginjo at least 50%. “Futsushu,” or “table sake,” does not have a set polishing ratio.

Generally speaking, the more polished rice becomes, the more expensive the final product will be due to smaller yields, as well as the work required for such significant milling. Highly polished styles like ginjo and daiginjo typically have fruity aromas, light body and cleaner flavors. The focus on ginjo style sake is relatively new, as a result of the lifting of taxes on sake with higher rice polishing ratios, and the new consumer demand for refined products.

Different types of sake illustration

Overall production of different types of sake in 2017. Futsushu continues to be mass-produced but premium sake is growing in demand.

Although a lot of attention is given to rice polishing ratio by sake professionals and industry competitions, it’s important to not get too caught up in analyzing digits. You might miss out on other good sake if you rely too heavily on it! Judging sake solely by polishing ratio is not the best way to find your favorite sake. Each sake has a character of its own that is reflective of where it was brewed and sourced in Japan. Trying sake from different categories is a great way to expand your sake knowledge and enhance your drinking experience.

What of sake should you start with? Read on for Lesson 4: Types of sake.


*1 National Tax Bureau Sake Production 2017

Next Lesson 4: Types of Sake

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