By Yoshi | Japan Unveiled
Most people who drink sake have never been inside the building where sake is made. I have visited three sake breweries (sakagura) in my life — one in the Nada district of Kobe, one in Fushimi near Kyoto, and one in the Yamagata Prefecture mountains — and each time I have walked into the specific building where fermentation is happening, the experience has been the same: a specific cold, a specific smell, and a specific humility in the face of a process that is so specific in its requirements and so complex in its execution that understanding it fully requires years of dedicated apprenticeship.
The sake brewing process — the specific sequence of steps that transforms ordinary rice into the specific clear, complex, subtly flavoured wine that is Japan’s most celebrated fermented beverage — is one of the most technically demanding food production processes in the world. Understanding it does not require becoming a brewer. But knowing the specific steps, the specific challenges, and the specific decisions that the tōji (杜氏 — master brewer) makes at each stage transforms the experience of drinking sake from passive consumption into an informed appreciation of what the specific liquid in the cup represents.
The Foundation: Rice, Water, and Koji
All sake production begins with three specific ingredients whose specific quality determines the specific quality ceiling of the sake that can be produced from them.
The rice. Not all rice is sake rice. The specific varieties developed for sake production — Yamada Nishiki, Gohyakumangoku, Omachi, Miyama Nishiki, and approximately one hundred other registered sake rice varieties — have specific characteristics that distinguish them from table rice: larger grain size, lower protein content, higher starch content, and a specific large starchy core (shinpaku — 心白) that is visible as a white spot in the centre of the polished grain.
The shinpaku is critical because it is the specific site where koji mould grows most readily — the large starchy core provides the specific substrate that the koji enzymes need to produce the specific sugars that yeast will subsequently ferment. A rice variety without a prominent shinpaku cannot be used for premium sake production.
The polishing. Before sake production begins, the rice is polished — the outer layers of the grain are removed by abrasion, reducing the grain to the specific size ratio required for the specific sake style being produced. The seimaibuai (精米歩合 — polishing ratio) is expressed as the percentage of the original grain remaining after polishing: a seimaibuai of 70% means 30% of the grain has been removed; a seimaibuai of 50% means half the grain has been removed.
The significance: the outer layers of the rice grain contain higher concentrations of proteins and lipids that produce specific complex flavours in the fermented sake — flavours that premium sake styles (ginjo and daiginjo) specifically exclude by polishing them away. The premium daiginjo sake requires polishing to 50% or below — a process that takes many hours, generates significant heat (which must be managed carefully to avoid damaging the starch structure), and reduces the raw material by at least half.
The water. Sake is approximately 80% water, and the specific mineral composition of the water used in brewing has profound effects on the specific character of the finished sake. The specific chemistry: the magnesium and phosphoric acid in hard water stimulate yeast activity and produce bolder, more robust sake; the softer water of certain regions (particularly Fushimi near Kyoto) produces the specific gentle, delicate sake style associated with that area. The specific water of each major sake production region is part of that region’s sake identity.
Koji: The Most Critical Step
The production of kōji (麹) — rice inoculated with the mould Aspergillus oryzae — is the most specifically critical step in sake production and the step that demands the most specific attention and skill from the toji.
The challenge: sake yeast cannot directly ferment rice starch. Rice starch must first be broken down into fermentable sugars (primarily glucose and maltose) before yeast can convert them to alcohol. In beer brewing, this conversion is performed by enzymes from malted barley, added at high temperature in the mashing process. In sake brewing, the equivalent enzyme production occurs through the growth of koji mould on cooked rice at a specific temperature and humidity — a living process that requires specific management across forty-eight hours of continuous attention.
The specific koji production process: cooked rice is spread on specific wooden boards in a specific room (kojimuro — 麹室) maintained at specific temperature (approximately 28-32 degrees Celsius) and specific humidity. Koji mould spores are distributed over the rice. The mould begins to grow, producing specific enzymes (amylases and proteases) that will later break down the rice starch and proteins in the main fermentation vessel.
The specific toji’s work during koji production: checking the temperature every two hours, adjusting the covering to manage humidity and heat, evaluating the specific visual appearance and specific aroma of the developing koji at each stage. The koji at various stages of its development has specific visual characteristics — the specific white mycelium growth, the specific degree of penetration into the rice grain — that the toji reads as indicators of whether the development is proceeding correctly.
The most critical moment: approximately thirty-six hours into koji production, the mould’s metabolic activity peaks and the temperature rises rapidly. This specific temperature spike must be managed precisely — too cool and the koji underdevelops; too hot and the enzymes are denatured and the koji is ruined. The toji who manages this specific moment correctly produces the specific koji that the specific sake requires.
Shubo: Building the Yeast Starter
The shubo (酒母 — sake mother) or moto (もと — origin) is the specific concentrated yeast starter that provides the vigorous yeast population required for the main fermentation. Its production is a specific protective measure: by establishing a large, healthy yeast population in a small, acidic environment before adding the full quantity of ingredients, the brewer creates a specific competitive advantage for the sake yeast against contaminating bacteria and wild yeasts.
The two major shubo styles:
Bodaimoto and Kimoto (生酛 — traditional starter): the historic methods in which the natural acidification of the starter occurs through the specific activity of naturally occurring lactic acid bacteria that are present in the brewing environment. The kimoto method — which involves the specific labour-intensive process of yamaoroshi (山卸し — repeatedly mashing the rice with long poles to break it down and mix it) over many hours — is considered the most demanding and most traditional of the starter methods. The sake produced from kimoto starters is often described as having more complexity, more mineral depth, and more specific structural solidity than sake produced by the modern quick method.
Sokujomoto (速醸元 — quick starter): the modern method, introduced in 1909, in which lactic acid is added directly to the starter, eliminating the two to four week acidification process of the traditional methods and reducing starter production time to approximately one to two weeks. The majority of contemporary sake is produced using the quick starter method.
The Moromi: Three-Stage Addition and Simultaneous Saccharification
The moromi (醪 — main mash) — the specific vessel in which the final fermentation occurs — is built using the specific sandan shikomi (三段仕込み — three-stage addition) process, in which the koji, cooked rice, water, and shubo are added to the fermentation vessel in three specific additions over four days.
The reason for three stages rather than one: adding all the ingredients simultaneously would excessively dilute the yeast concentration built in the shubo, slowing fermentation and potentially allowing contaminants to establish before the yeast can dominate. By adding the ingredients in increasing quantities over several days, the yeast population maintains a specific minimum concentration and competitive advantage at each stage.
The specific miracle of sake fermentation: sake is the only alcoholic beverage in the world in which saccharification (the conversion of starch to sugar) and fermentation (the conversion of sugar to alcohol) occur simultaneously in the same vessel. Beer production separates these two processes — mashing produces sugar, then fermentation converts it. The simultaneous process of sake fermentation — koji continuously converting rice starch to sugar while yeast continuously converts the resulting sugar to alcohol — allows the alcohol content to reach the highest level of any naturally fermented beverage (up to 22% ABV before dilution), because the specific rate of saccharification can be managed to always provide slightly more sugar than the yeast can immediately consume, maintaining yeast activity without the sugar excess that would produce off-flavours.
Pressing, Filtering, and Maturation
After approximately thirty to forty days of moromi fermentation, the mash is pressed — the liquid sake separated from the solid rice lees (sake kasu) — through a specific pressing process using a traditional pressing machine (fune — 舟) or, in modern breweries, a continuous pneumatic pressing system.
The specific first pressing stage — arabashiri (荒走り — rough run) — produces sake of high turbidity and high fragrance as the pressure first begins to express liquid from the mash. This early pressing is bottled separately by some breweries as a specific product. The main pressing — nakadori (中取り) or nakazumi — is considered the finest expression of the moromi, expressing cleanly with minimal turbidity. The final pressing — seme (責め) — is the most forceful extraction, producing sake that is less delicate and typically used for blending or for second-grade products.
The pressed sake undergoes specific filtration and pasteurisation processes that vary by style and by brewery philosophy. The namazake (生酒 — unpasteurised sake) that many enthusiasts specifically seek is sake in which pasteurisation has been omitted, preserving the specific fresh, slightly yeasty character of the unprocessed product — but requiring refrigerated storage and relatively rapid consumption.
— Yoshi 🍶 Central Japan, 2026
Enjoyed this? You might also like: “Sake: A Beginner’s Guide to Japan’s Most Misunderstood Drink” and “Shochu: Japan’s Other Spirit — Why It Deserves More Respect” — both available on Japan Unveiled.
