The most important characteristic that defines the quality level of Sake is Seimai Buai, also called rice polishing ratio. For high quality Sake the rice grain is polished, in order to remove the outer layers and only leave the pure starch at the center of the grain. Seimai Buai represents the amount of rice left after polishing, so the lower numbers indicate higher quality.
There are several different types of sake. The following special designations (called Tokutei meisho) are defined by the Japanese government.
All sake in Junmai categories are brewed from polished rice and water only. For other premium sake it is allowed to add brewer’s alcohol under 10% of rice weight.
For non-premium sake it is allowed to add more alcohol and other ingredients like glutamate.
In honjozo-shu, the emphasis is on flavor and there is little ginjo-ka or aging‐induced aroma. It has a reasonable level of acidity and umami and rather than asserting the aroma and taste of the sake itself, it helps to bring out the taste of food.
Ginjo-shu is made with rice grains from which more than 40% of the outer layer has been removed by milling. Fermentation occurs at lower temperatures and takes longer. Distilled alcohol equivalent to up to 10% of the weight of the polished rice may be added.
It has a fruity fragrance, called ginjo-ka, with a light taste, that is low in acidity. “Light” does not simply mean “mild” or “diluted.” The sake should also have a smooth texture (mouth feel) and a good aftertaste.
The specific characteristics of ginjo-shu vary by brewer, with the more fragrant varieties designed to highlight ginjo-ka and others designed with more emphasis on flavor and less on ginjo-ka.
Daiginjo-shu is a form of ginjo-shu made with even more highly polished rice from which at least 50% of the outer layer of the grain has been removed. It has an even more refined taste and stronger ginjo-ka than ginjo-shu.
Junmai-shu and tokubetsu junmai-shu are made only from rice, koji and water, highlighting the flavor of the rice and koji more than other varieties. There are no requirements regarding polishing ratio. Junmai-shu is typically high in acidity and umami, with relatively little sweetness.
Because ginjo brewing techniques are used in making junmai ginjo-shu, the acidity and umami are toned down and there is a clear ginjo-ka.
Junmai daiginjo-shu is regarded as the highest-grade sake. The best products in this class deliver a good blend of refined taste with acidity and umami.
As a further way to classify Sake, not as strictly defined as the government regulation, Sake varieties can also be distinguished by brewing method. Here arethe most common definitions.
Sake brewed during the current year.
Matured Sake that has been stored for a long time. Period of maturation can be authenticated.
Undiluted sake. Many genshu have a high alcohol content and have strong taste, because there is no addition of water after pressing.
Hand-made Junmai-shu or honjozo-shu that has been brewed using certain traditional methods.
Usually, sake is pasteurized twice before being bottled, however this is sake bottled without being pasteurized at all.
Nama-chozo-shu is sake pasteurized only once at bottling after maturation.
Namazume-shu is bottled sake pasteurized only once before maturation.
This term derives from ancient Japanese book Engishiki, which records a unique mixing process, shiori, using sake instead of water in the brewing process. There are sub-varieties of Kijoshu, such as koshu, namazake etc.
The term means junmai-shu brewed at only one brewery, rather than having been blended from more than one brewery.
Cask sake. sake that has been kept in a cedar cask, has its own special aroma.
This is an old-style way of marketing namazume-shu. It refers to sake that has been pasteurized only once and aged from the winter until the following fall before marketing.
The moromi is filtered through a coarse cloth which produces cloudy sake, called nigorizake. In the past, it was unpasteurized and contained living yeast. However, these days, much of the nigorizake is pasteurized to stabilize the quality.