As this chart indicates, the six main sake classifications are influenced by two main factors: sake ingredients and the rice polishing/milling percentage.
Rice is milled or “polished” before being used in brewing to eliminate the fats, proteins, and minerals on the outer portions of the grain that can inhibit fermentation and cause off flavors in the finished product. In general, the more the rice has been polished, the more refined and elegant the sake flavor profile will be. The polishing rate is called seimaibuai.
Junmai Daiginjo is ultra premium pure sake and has a very light, fragrant, fruity and subtle taste. It is brewed with rice where each grain has been polished away by 50% at the minimum, and the various brewing processes are handled with greater care and attention to detail. These expressions are the pinnacle of sake brewing.
Ginjo is pure sake brewed with rice whose each grain has been polished away by 40-50%. Like Junmai Daiginjos, the flavor of Junmai Ginjo sake is light, fragrant and even complex.
Pure sake brewed only with rice polished to a seimaibuai of 70%, filtered water, and kōji mold, junmai sake is robust, full-bodied, and slightly acidic. It goes well with a wide variety of food.
Honjozo is brewed with rice, filtered water, kōji mold and yeast. The grain of rice is polished by more than 30%. A small amount of distilled alcohol (brewer’s alcohol) is added in the final fermentation process to soften the rusticity of the sake. Honjozo is clean, dry, and smooth.
Though many things can affect whether a sake tastes sweet or dry (including acidity, serving temperature, mineral content of the brewing water, and previous dishes or accompanying food), one numerical guide that may be helpful, and can often be found on a bottle’s label, is the sake’s nihonshu-do or Sake Meter Value (SMV).
SMV is its specific gravity; the density of the sake compared to the density of water. Theoretically, the higher (positive) the number, the drier the sake should taste. Conversely, the lower (more negative) the number, the sweeter the sake might taste. An easy way to remember this relationship is the phrase, “High is dry.”
While the SMV scale is generally seen in the -5 to +15 range, it is important to remember that SMV value is a barometer and good reference point, but not completely accurate, as mentioned above, there are countless other factors affecting how one interprets sweetness and dryness.
Though traditional standards held that sake should be on the dry side, sweeter tasting sake has recently become more popular. Today’s SMV for a balanced sake is somewhere between +2 to +4.
The measure of the acid in sake. Acidity affects how the flavour spreads in the mouth, and also the sensation of sweetness and dryness. The range is quite narrow, with 0.7 being low and 2.0 being quite high. Acidity that is ~1.2 or so is average.
Sake Chilled vs Warm
Premium sake is much more delicate, balanced, fragrant, and complex than non-premium sake (sake with less stringent milling requirements). That's why premium sake is best when stored cold (~5°C) and enjoyed chilled (10°C). Heating sake tends to mask its refined flavours and complexity. When you heat a premium sake, you compromise its true expression -- essentially destroying the delicate flavours and nuances originally intended by the Tōji.
Other Types of Sake
Genshu is undiluted sake. Most sake is diluted with water after brewing to lower the alcohol content from 18-20% down to 14-16%, but genshu is not.
Kimoto means brewers introduce lactic acid into the fermentation process for cultivating yeast. Kimoto sake is allowed to naturally develop lactic acid on its own. This process takes four weeks from start to finish, consumes about twice as much time and effort as the normal brewing method and requires a technique that is extremely difficult to accomplish in a stable, consistent manner. Only a very few of more than 1,000 sake breweries in Japan employ it. The Kimoto method can be regarded as the most traditional and natural sake brewing method. This style offers very distinctive, broad, rich taste and deep flavour worth trying.
Muroka means unfiltered. It refers to sake that has not been carbon filtered, but which has been pressed and separated from the lees, and thus is clear, not cloudy. Carbon filtration can remove desirable flavors and odors as well as bad ones, thus muroka sake has stronger flavors than filtered varieties.
Namazake is sake that has not been pasteurised. It requires refrigerated storage and has a shorter shelf-life than pasteurized sake. It has a fresh taste.
Nigori is cloudy sake. The sake is passed through a loose mesh to separate it from the mash. It is not filtered thereafter and there is much rice sediment in the bottle. Before serving, the bottle is shaken to mix the sediment and turn the sake white or cloudy.
Tokubetsu junmai ("special pure") is a special designation for high-quality sake. To qualify as tokubetsu junmai, a sake must be made with rice polished to less than 60 percent of its original weight, and must not be fortified with distilled alcohol. If the brew has alcohol added to it, the classification drops to tokubetsu honjozo.