From Koji to Shubo: Building the Foundation of Fermentation

The Transition Begins

With the completion of koji, the process shifts—quietly but decisively—into its next phase: shubo.

Koji has already begun transforming the rice, unlocking sugars and setting the stage for fermentation. Now, that potential must be guided into something stable, alive, and ready to carry the brew forward.

This is where the yeast starter is born.

Bringing the Elements Together

Shubo is created by combining koji rice, steamed rice, water, and yeast in carefully measured proportions. What begins as separate components gradually becomes a unified, living culture.

At this stage, balance is everything.

The environment must be controlled, but not forced. Temperature, timing, and proportion all play a role in how the yeast develops. Too rapid a start can lead to instability and too slow, the process loses momentum.

The brewer watches closely—adjusting, responding, and allowing the mixture to evolve at its own pace and inside the tank, activity begins to build.

The yeast establishes itself, feeding on the sugars made available by the koji. Acidity rises, creating a protective environment that ensures only the desired microorganisms thrive. Like the koji before it, this stage cannot be rushed. It is a gradual, deliberate process, where each day brings subtle but important changes.

Precision and Intuition

Shubo is both technical and deeply intuitive.

While measurements and methods guide the process, the brewer relies just as much on observation and experience. Each batch carries its own pace and this is where science meets craft.

Every decision made here will echo throughout fermentation, influencing the structure, clarity, and character of the final sake.

The Foundation Takes Shape

By the end of this stage, the yeast starter is strong, balanced, and ready.

It may appear simple, but within it lies the groundwork for everything to come.

Just as the koji quietly transformed the rice—grain by grain—shubo builds the living foundation of sake, preparing it for the long, thoughtful journey ahead.

Continuing the Journey

At Hachidori, this step is approached with the same patience and attention as every stage before it—honoring the belief that great sake is not rushed, but revealed over time.

Follow along as we move into the next stage of fermentation.