In the previous articles, we reviewed parallel multiple fermentation and dan-jikomi (staged additions).
Kōji creates sugars, and yeast produces alcohol. Dan-jikomi is the method that keeps that mechanism stable.
But what happens after fermentation is complete?
This is where hi-ire (pasteurization) comes in.
What Is Hi-ire?
Hi-ire is the process of heating sake to approximately 60–65°C (140–149°F).
Even after fermentation has finished, yeast and enzymes do not completely stop working. If left untreated, the flavor can continue to change and the quality may become unstable.
Hi-ire temporarily halts these activities and stabilizes the condition of the sake.
When Did Hi-ire Begin?
Hi-ire is not a modern invention. Historical records suggest that heat treatment was already practiced during the Muromachi period.
At that time, refrigeration did not exist, and sake was highly susceptible to spoilage during storage. Microorganisms and enzymes continued to act even after fermentation, making stability a major challenge.
Heating to stop these activities was a practical solution to improve preservation. Hi-ire developed not to change flavor, but as a technology to protect quality.
Why 60–65°C?
There is a clear reason for the 60–65°C temperature range.
Yeast begins to rapidly lose activity above 50°C and becomes largely inactive around 60°C. Enzymes derived from kōji also weaken significantly in this range.
At higher temperatures, however, aromatic compounds may be negatively affected. Therefore, 60–65°C represents a balanced temperature that stops microorganisms while minimizing damage to flavor.
How Long Is It Heated?
Time is just as important as temperature. Typically, sake is held in this temperature range for several minutes.
Modern breweries often use plate heat exchangers to heat the sake quickly and evenly, followed by rapid cooling. By precisely controlling temperature and time, stability is achieved without sacrificing quality.
Differences Between Namazake and Other Types
The number and timing of hi-ire treatments determine the classification of sake.
- Namazake: No pasteurization at all
- Nama-chozō-shu: Not pasteurized before storage, pasteurized once before shipment
- Nama-zume-shu: Pasteurized once before storage, not pasteurized before shipment
- Standard sake: Pasteurized twice (before storage and before shipment)
The difference is not simply whether pasteurization occurs, but how many times and at what stage.
Why Does Namazake Require Refrigeration?
Namazake is bottled without any pasteurization.
This means yeast and enzymes have not been fully inactivated.
If stored at room temperature, residual yeast or enzymes may continue to act, leading to changes such as:
- Renewed fermentation and gas production
- Increased acidity
- Aroma changes
- Cloudiness
Refrigeration slows microbial and enzymatic activity. The lower the temperature, the slower these reactions proceed.
Namazake is delicate and fresh, but also more prone to change. Proper temperature control is essential to preserve its character.
Relationship to Parallel Multiple Fermentation
Parallel multiple fermentation is the core of sake brewing.
Hi-ire can be understood as the step that stops that fermentation. Sake brewing is not only about how fermentation proceeds, but also about when and how it is stopped.
Conclusion
Hi-ire plays a critical role in protecting the quality of sake.
- Stops fermentation
- Suppresses enzymatic activity
- Stabilizes the final product
Sake brewing is precisely designed not only to create fermentation through parallel multiple fermentation, but also to determine when to halt it and preserve the desired profile.
▶ Moving to the Final Stage
Now that pasteurization has stabilized the sake, how is it prepared for delivery to consumers?
From Pressing (Jōsō) to Bottling — A Complete Guide to the Final Steps
We will examine the flow from pressing (jōsō) to blending, dilution (wari-mizu), and bottling, and look at the full picture of how sake is completed.
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