How Sake Is Made: A Visitor's Guide to Japan's Ancient Brewing Art

The moment you step inside a sake brewery in winter, something shifts. The air is dense and warm, heavy with the smell of steamed rice and something fermented and alive. It is not an industrial smell. It is ancient, quiet, and oddly beautiful.

Most visitors to Japan have tasted sake. Few understand what they are tasting, or why a glass of junmai daiginjo from a small Niigata brewery tastes so completely unlike anything else in the world. The answer lies in one of the most complex and demanding fermentation processes on earth — one that has been refined over more than a thousand years.

This is a guide to how sake is made, written for curious travelers who want to understand what they are seeing when they step inside a Japanese brewery.

It Begins with Rice — but Not Just Any Rice

Sake is brewed from rice, water, yeast, and a mold called koji. That is the simple version. The details are where the story begins.

Not all rice is sake rice. Japan has dozens of dedicated sake rice varieties — Yamada Nishiki, Gohyakumangoku, Omachi, Yukinosei — each with different starch structures, water absorption rates, and flavor profiles. Sake rice grains are larger and starchier than table rice, bred specifically to allow the deep penetration of koji mold.

Before brewing begins, the rice is milled — polished down to remove the outer layers of bran and protein. This step, called seimai, is measured as a percentage. A rice polishing ratio of 70% means 30% of the grain has been removed; 50% means half the grain is gone. The more a brewer polishes the rice, the lighter, cleaner, and more refined the sake tends to be. Ginjo sake (the premium category) is polished to at least 60% remaining; daiginjo (the most refined) to at least 50%.

Milling can run for a day or more, slowly reducing a bag of grain to something almost luminous — the first sign that sake brewing is an exercise in patience.

The Soul of Sake: Koji

Nowhere in sake brewing is the skill of the toji (master brewer) more visible than in the koji room.

Koji is a benign mold (Aspergillus oryzae) that, when cultivated on steamed rice over 40 to 50 hours, produces enzymes that convert rice starch into fermentable sugars. Without koji, the yeast would have nothing to eat. Without sugar, there is no fermentation. Without fermentation, there is no sake.

The koji room is typically the most carefully controlled space in a brewery: warm, humid, and strictly protected from contamination. The temperature inside hovers around 30°C. The brewer — or a small team — tends the rice by hand at regular intervals through the night, spreading it, turning it, feeling its temperature with their palms.

Whether a visitor can see the koji room depends on the brewery and the season; it is one of the rare spaces some breweries open to guests. Where it is possible, the warmth hits you immediately, and the white bloom of mold across the rice looks impossibly delicate for something so central to the process.

Multiple Parallel Fermentation

What makes sake scientifically remarkable — and practically unlike any other fermented beverage — is a phenomenon called heiko fukuhakko: multiple parallel fermentation.

In winemaking, sugar is already present in the grape. Yeast converts that sugar directly into alcohol. In beer brewing, malting converts grain starch to sugar first; fermentation happens afterward, in sequence.

In sake brewing, both conversions happen simultaneously, in the same vessel. Koji enzymes are constantly breaking down starch into sugar while yeast is simultaneously converting that sugar into alcohol. The brewer manages both processes at once, in real time, adjusting temperature and proportion to achieve the desired flavor.

This parallel process is why sake can achieve alcohol levels of 18 to 20% naturally — far higher than wine or beer — without distillation.

The fermentation mash (moromi) is built in stages over three or four days, a technique called sandan jikomi: three separate additions of steamed rice, koji, and water. This controlled buildup allows the yeast to establish itself before being overwhelmed by volume.

Water: The Silent Ingredient

Ask any sake brewer what matters most, and water will be among the first answers.

Sake is more than 80% water. The mineral content of brewing water affects fermentation speed, enzyme activity, and the final character of the sake in ways that are precise and deeply local. Hard water — rich in minerals like potassium and magnesium — accelerates fermentation and tends to produce drier, more vigorous sake. Soft water slows fermentation and tends toward gentler, more delicate expression.

This is why Niigata sake tastes the way it does. The soft water drawn from snowmelt filtering through the Echigo mountains produces sake with a characteristic lightness and clarity — what drinkers call tanrei karakuchi: clean and dry. The water at Hakkaisan, drawn from the snowfields of Mt. Hakkai, has been shaping the brewery's character for generations. At Aoki Shuzo, the water from Minami-Uonuma — the same region famous for Koshihikari rice — carries its own quiet mineral profile.

In Yamanashi, Shichiken draws water from the Southern Alps, where snowmelt from the mountains feeds the water the brewery uses.

Pressing, Filtering, and the Final Character

After three to five weeks of fermentation, the sake is pressed. The moromi — a thick, porridge-like mash — is run through a press that separates the liquid sake from the spent rice solids (sake kasu). In some breweries, this pressing is done slowly, using cloth bags stacked in a traditional press called a fune.

What comes out is raw, unpasteurized sake (nama sake). Most sake is then pasteurized twice — once after pressing and once before bottling — to stabilize the flavor and extend shelf life. Nama sake skips this step entirely, preserving an alive, almost electric freshness that changes as you hold it on the palate.

Some sake is filtered through activated charcoal to remove color and adjust flavor; unfiltered sake (muroka) carries a faint golden hue and a fuller, wilder character. Some is diluted with water before bottling to lower the alcohol; undiluted sake (genshu) is bottled at full strength, dense and often warming.

Why It Matters to Visit

You can read about koji and sandan jikomi indefinitely. It is another thing entirely to stand inside a brewery in winter, in the season when the work is happening, and smell the air.

Sake is a craft that resists industrial shortcuts. The best producers in Niigata and Yamanashi are small family operations where a handful of people manage the entire process by season, by feel, by knowledge passed across generations. A private visit — arranged quietly, conducted in English, unhurried, and shaped around the season and what the brewery can offer that day — is a way of being present for something rare.

Wintage Tour arranges private access to some of Japan's most respected sake breweries in Niigata and wine producers in Yamanashi. Learn more about what to expect on a private brewery visit, or explore the Niigata sake region in depth.