Yeast and Fermentation in Japanese Sake

Did you know?

That a single grain of rice undergoes an invisible drama of “life” before becoming that aromatic Japanese sake you love.

In the quiet of the sake brewery, bubbles gently rise to the surface. Beneath them, yeast organisms are performing the magic of fermentation with their very lives at stake.

This article will guide you into the “stage of microorganisms” behind the creation of Japanese sake. By the time you finish reading, you’ll surely want to savor a cup of sake slowly and thoughtfully.

In the quiet brewery, bubbles gently float on the tank surfaces. There, invisible life forms are creating the miracle of transforming rice into sake. This article unravels the mystery of “fermentation” that supports Japanese sake.

What is Yeast?

The Role of Yeast

Yeast is a type of microorganism that breaks down sugars to produce alcohol and carbon dioxide. In sake brewing, specialized yeast called “sake yeast” is used to transform the sweetness of rice into flavorful sake.

Characteristics of Sake Yeast

• High alcohol tolerance (approximately 18-20%) enabling robust fermentation
• Low-temperature fermentation capability that brings out delicate aromas and flavors
• Production of fragrant compounds (such as ethyl caproate) creating elegant aromas
• Stable fermentation power maintaining consistent quality

What is Parallel Fermentation?

A Rare Fermentation Style Worldwide

In sake brewing, two processes called “saccharification” and “fermentation” occur simultaneously in the same tank. This is called “parallel fermentation.”

1. Saccharification: Koji mold breaks down rice starch into glucose
2. Fermentation: Yeast converts sugar into alcohol
3. Simultaneous process: These two processes occur simultaneously and continuously, achieving high alcohol content and rich flavor

Differences from Other Alcoholic Beverages

Beverage Type	Saccharification	Fermentation	Characteristics
Wine	Not needed (fructose)	Single fermentation	Direct fermentation of fruit sugars
Beer	Saccharification first	Fermentation in separate tank	Sequential complex fermentation
Japanese Sake	Saccharification and fermentation simultaneous	Same tank	Parallel fermentation

Three-Stage Brewing (Sandan-jikomi)

The Process and Meaning of Brewing Stages

Adding large amounts of ingredients at the beginning of fermentation prevents yeast from working properly. Therefore, sake uses “three-stage brewing” where ingredients are added in three separate additions.

1. Hatsuzoe (First addition): Preparation stage to establish yeast environment
2. Odori (Dancing): “Rest day” for yeast multiplication
3. Nakazoe (Middle addition): Adding ingredients to intensify fermentation
4. Tomezoe (Final addition): Final stage of brewing that determines the sake’s structure

This process stabilizes fermentation and creates the complex, mellow flavors characteristic of Japanese sake.

Fermentation Period and Temperature Control

Duration of Fermentation

• Regular sake: Approximately 18-25 days
• Ginjo sake: Approximately 25-35 days
• Daiginjo sake: Up to 40+ days

Relationship Between Temperature and Flavor

Fermentation Temperature	Characteristics	Suitable Sake Types
High temperature (15-18°C)	Fast fermentation, robust flavors	Regular sake, etc.
Low temperature (10-13°C)	Slow progression, delicate aromas	Ginjo, Daiginjo

Types of Yeast

Kyokai Yeast

Standard yeast distributed by the Japan Brewing Society, supporting quality standardization across breweries.

• No. 6: Suitable for classic junmai sake
• No. 7: Well-balanced aroma and flavor
• No. 9: Strong ginjo aroma, elegant
• No. 1801 (Improved No. 9): Stronger aroma and lower acidity

Kuratsuki Yeast (Natural Yeast)

Yeast that naturally occurs in sake breweries, forming unique flavors through years of fermentation environment.

• Strongly reflects brewery individuality
• “Variation” from wild yeast is also part of the charm

Fermentation Management and Pressing

Daily Observation and Control

Toji (master brewers) and brewery workers daily check tank temperature, bubbles, aroma, sugar content, pH, and other factors to monitor fermentation progress. This requires a fusion of craftsman’s “intuition” and scientific analysis.

What is Joso (Pressing)?

The process of pressing sake from fermented “moromi.” There are several methods:

1. Bag pressing: Traditional method where sake naturally drips
2. Yabuta pressing: Mechanical method, most common approach
3. Centrifuge: Cutting-edge technology for highest quality

Summary

Sake fermentation is an art born from the harmony between “nature” and “humans.” The activities of microorganisms, guided by the toji’s skill, nurture the profound cup that is Japanese sake.

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For more detailed information, please also read How Sake is Made.