Sake Explained: Koji, Polished Rice, Grades and How to Order a Cup

Sake is often called rice wine, but it is brewed more like beer than like grape wine. Steamed rice is transformed by a mold called koji, yeast turns the resulting sugars into alcohol, and the mash is pressed and aged into one of the most nuanced drinks in the world. In Japan it is properly called nihonshu (Japanese alcohol), while the word sake in Japanese can refer to alcohol in general.

This guide walks through how sake is made, what the grades on the label mean, why the same bottle can taste wonderful chilled and entirely different warm, and how to order with confidence at an izakaya (casual Japanese pub), a specialist sake bar or a restaurant. Along the way you will pick up the vocabulary that makes a long sake list far less intimidating.

Not Quite Wine, Not Quite Beer

Wine makers rely on sugar already in the grape. Rice contains starch instead, so a sake brewer has to turn that starch into sugar before yeast can do its work. Beer makers do this in a separate step. Sake brewers do it in the same tank at the same time, a process called multiple parallel fermentation, which is one reason sake can reach an alcohol level of about 18 to 20 percent before it is diluted. Most bottles are blended down with water to around 14 to 16 percent.

The result is a drink with flavors of melon, pear, steamed rice, cream, mushroom or sea breeze, depending on the style. Because sake is made from rice and water with very little else, small decisions about rice, water, temperature and timing leave a clear fingerprint on the finished taste.

Rice, Water and the Role of Koji

Sake rice is not the same as the rice served at dinner. Varieties such as Yamada Nishiki, widely associated with Hyogo Prefecture, and Gohyakumangoku, associated with Niigata and the Hokuriku region, have larger grains with a starchy white core that suits brewing. Water matters as much, since it makes up most of the finished drink. Famous brewing districts such as Nada in Hyogo and Fushimi in Kyoto are known for their local water, which shapes whether a sake tastes firm and dry or soft and round.

Koji is the quiet hero. Spores of the mold Aspergillus oryzae are scattered over steamed rice in a warm, humid room, and the enzymes they produce break starch into sugar. The same mold is used to make miso and soy sauce. A toji (master brewer) and a team of kurabito (brewery workers) tend the koji by hand, sometimes through the night, because the temperature must be watched with great care.

How Sake Is Brewed

The brewing year traditionally runs through the cold months, when low temperatures keep fermentation slow and clean. After the rice is polished, washed, soaked and steamed, part of it becomes koji. Another portion goes into a small starter called shubo or moto, where yeast is cultivated before the main mash begins.

The main mash is built in three stages over four days, a method called sandan shikomi: the first addition on day one, a rest on day two, then a second addition on day three and a final one on day four. Fermentation then continues for roughly two weeks, longer in some cases. Ginjo-style sake is fermented slowly at cool temperatures, around 5 to 10 degrees Celsius, which helps create its fruity aroma. When the mash is ready it is pressed, filtered, usually pasteurized, and then stored, often for several months, before it is bottled. Some sake is aged for a year or more, and a rare style called koshu (aged sake) can develop amber color and nutty depth.

Polishing and the Grades on the Label

Every bottle carries a seimai-buai, the percentage of each rice grain that remains after polishing. A rating of 60 percent means 40 percent has been milled away. Polishing removes proteins and fats from the outer layers, and lower numbers generally lead to a cleaner, more fragrant sake, though the best choice depends on taste rather than rank.

Here is how the main premium categories work. Junmai means rice, water, koji and yeast only, with no added distilled alcohol and no minimum polishing requirement. Honjozo uses rice polished to at most 70 percent with a small amount of distilled alcohol added. Ginjo requires rice polished to at most 60 percent, and daiginjo to at most 50 percent. Add the word junmai in front, as in junmai ginjo or junmai daiginjo, and it means no distilled alcohol was added. Distilled alcohol in the other grades is not a flaw; it can lift aroma and make the finish lighter.

Styles Worth Knowing

Beyond the main grades, a handful of words appear on many labels. Nigori is cloudy sake with some rice solids left in, usually softer and sweeter. Namazake is unpasteurized sake, fresh and lively, normally kept cold. Genshu is undiluted sake, richer and stronger. Sparkling sake has gained popularity in recent years, and sweet and dry styles both exist.

Dryness is often shown by the nihonshu-do, or sake meter value. A positive number points toward dry and a negative number toward sweet, although acidity and aroma also change how the taste is perceived. Do not worry about chasing a number. A better approach is to describe what you like, such as light and fruity, dry and crisp, or rich and rounded, and let the staff recommend a bottle.

Serving Temperature and Vessels

Few drinks respond to temperature as dramatically as sake. Reishu (chilled sake) is served at about 10 degrees Celsius, which suits delicate ginjo and daiginjo. Atsukan (hot sake) is served at about 50 degrees Celsius and brings out sweetness and body in sturdy junmai and honjozo styles. Room temperature is called jo-on, and there are several in-between steps, each with a poetic name, spaced about five degrees apart. Premium sake is usually enjoyed cool rather than hot.

Sake arrives in a tokkuri (small ceramic flask) with ochoko (tiny cups), in a glass, or in a masu (square wooden box) that holds one go, about 180 milliliters. At some restaurants the server pours until the glass overflows into the masu as a gesture of generosity. Pour for your companions and let them pour for you, holding the cup with both hands when receiving. Say kanpai (cheers) before the first sip.

How to Order and Plan Your Visit

At an izakaya, ask for the osusume (recommendation) and mention whether you prefer dry or sweet, light or rich, cold or warm. Many sake bars offer a nomikurabe, a tasting set of three small glasses, which is the easiest way to compare styles. Sizes are often listed by go, with one go equal to about 180 milliliters, so a half portion may appear on the menu too. Sake pairs well with fish, tempura, grilled chicken skewers and even cheese.

For a deeper dive, visit a brewery. Fushimi in Kyoto, Nada in Kobe, Saijo in Hiroshima Prefecture and many towns in Niigata welcome visitors with tours, tastings and museums, though hours and reservations vary, so check each brewery's official site. A ball of cedar branches hung outside a brewery, called a sugidama, traditionally announces the new season's sake. October 1 is celebrated in Japan as Sake Day. Remember that the legal drinking age in Japan is 20, and never drive after tasting.