How is Sake Made? Basics of Fermentation

Brewing Mechanisms
2025.03.02

Hello! I’m Mana. Lately, as I’ve been studying for the Sake Certification, I keep finding new surprises—especially about how sake is actually made. Today, I’d like to introduce one of the most important foundations of sake brewing: fermentation.

Hello, I’m Mana. As I continue studying for the Sake Certification, the very first topic I want to understand clearly is fermentation.

Sake is made from rice, but rice doesn’t become alcohol on its own. Behind the scenes, there is a system called fermentation, powered by microorganisms—mainly koji and yeast.

In this article, I’ll整理 the basics of sake fermentation in the simplest way possible.

What Is Fermentation? How It Relates to Sake

Fermentation is a process in which microorganisms transform ingredients into different substances. In the world of food and drink, many products are made through fermentation—bread, yogurt, wine, and beer are classic examples.

In sake, the main process is alcoholic fermentation. A microorganism called yeast converts sugar into alcohol and carbon dioxide, and it also produces aroma compounds (such as esters). The fruity notes you may notice in sake often come from these fermentation by-products.

However, sake fermentation works a little differently from wine. This is a key point.

The Role of Koji: Turning Starch into Sugar

The main ingredient of sake is rice, but rice does not contain enough sugar from the start. The primary component of rice is starch.

This is where koji becomes essential. Koji mold (mainly Aspergillus oryzae, also called yellow koji mold) produces enzymes that break starch down into glucose. This process is called saccharification.

So in sake brewing, you first need a step that converts “rice starch into sugar.” Without sugar, yeast cannot produce alcohol.

Sake mainly uses yellow koji mold. In contrast, awamori often uses black koji mold, and shochu often uses white koji mold. Different koji molds can influence the character of the final drink.

The Role of Yeast: Turning Sugar into Alcohol

Once koji creates sugar, yeast converts that sugar into alcohol. This is called alcoholic fermentation.

Yeast breaks down sugar and produces alcohol and carbon dioxide. At the same time, it creates aromatic compounds such as esters, which can become the source of the elegant “ginjo aroma.” In other words, the choice of yeast can strongly affect a sake’s aroma and flavor.

For example, some ginjo yeasts can produce apple- or melon-like notes. Choosing the right yeast is one of the key factors that shapes a sake’s identity.

Single Fermentation, Multiple Fermentation, and Parallel Multiple Fermentation

There are three major fermentation “structures” to know:

  • Single fermentation: The ingredient already contains sugar, and yeast directly converts it into alcohol (e.g., wine).
  • Multiple fermentation: Saccharification and fermentation happen in separate steps (e.g., beer).
  • Parallel multiple fermentation: Saccharification and fermentation proceed at the same time (sake).


Sake uses a unique system called parallel multiple fermentation, where koji converts starch into sugar while yeast simultaneously converts that sugar into alcohol. This method is rare even on a global scale.

Because sugar is continuously supplied, yeast can keep working for a long time. As a result, sake often reaches a relatively high alcohol content—around 15%. This is one reason why sake is typically stronger than wine (often around 12%).

Temperature Control Is Critical in Fermentation

In sake fermentation, temperature control is extremely important. If the temperature is too high, yeast activity becomes too vigorous, and unwanted flavors can appear more easily.

On the other hand, Ginjo and Daiginjo are fermented slowly at low temperatures. This is often called low-temperature, long-term fermentation, and it is one of the techniques used to draw out refined, aromatic profiles.

Fermentation is a natural phenomenon—but in sake brewing, human technique carefully “designs” the result.

Summary: The Basics of Sake Fermentation

Let’s recap the key points:

  • Sake is made through fermentation powered by koji and yeast.
  • Koji turns starch into sugar (saccharification).
  • Yeast turns sugar into alcohol (alcoholic fermentation).
  • Sake uses parallel multiple fermentation, where saccharification and fermentation happen at the same time.

Once you understand this fermentation mechanism, the entire sake brewing process becomes much easier to see. Next, let’s look at how fermentation is built into the real production steps.

▶ Next Article

The Sake Brewing Process: How Rice Becomes Sake

If you grasp the full picture first, concepts like “parallel multiple fermentation” and “three-stage mashing” become much easier to understand.

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