Filtration and Pasteurization: The Combinations

“Muroka nama genshu.” “Namazume.” “Hi-ire.”

Sake labels feature various terms. These indicate the processing the sake has undergone.

Filtration and pasteurization. The combination of these two processes greatly influences sake’s style. Let’s explore the science and flavor impact.

What Is Filtration?

Purpose of Filtration

Freshly pressed sake contains various suspended particles.

What Filtration Removes

• Ori (lees): Yeast and rice particles
• Protein aggregates
• Components adsorbed by activated charcoal

Goals of Filtration

• Clarify the sake
• Remove off-flavors
• Adjust aroma and color

Types of Filtration

Ori-biki (Lees Removal)

• Let pressed sake sit
• Separate settled lees
• The most basic step

Filtration

• Remove particles through filters
• Increase clarity
• Various filter grades available

Activated Charcoal Filtration

• Adsorption treatment with activated charcoal
• Removes color, aroma, and off-flavors
• Creates light, refined sake

What Is Muroka (Unfiltered)?

Sake without activated charcoal filtration, or with only minimal filtration.

Characteristics

• Slight color (yellow to gold)
• Umami components retained
• Richer aroma
• Fresh impression

Labeling

• Often marked “Muroka”
• “Suro-ka” indicates light filtration only

What Is Hi-ire (Pasteurization)?

Purpose of Pasteurization

Hi-ire is heating sake to approximately 60-65°C.

Purposes

• Deactivate enzymes
• Sterilization
• Stabilize quality

Why Is Pasteurization Needed?

Enzyme Deactivation

• Sake contains enzymes from koji
• Active enzymes cause continuous flavor changes
• Hi-ire stops the enzymes

Sterilization

• Kills microorganisms in the sake
• Prevents spoilage and deterioration
• Improves shelf life

History of Pasteurization

Pasteurization was practiced as early as the Muromachi period.

Historical Background

• Technique discovered empirically
• Predates Pasteur’s pasteurization by over 300 years
• A preservation method suited to Japan’s climate

Number of Pasteurizations

Standard sake undergoes pasteurization twice.

First Pasteurization (Pre-Storage)

• Performed after pressing, before storage
• Stabilizes quality for aging

Second Pasteurization (Pre-Bottling)

• Performed before shipping
• Final quality stabilization

Types of Nama (Unpasteurized) Sake

Based on pasteurization timing, several types exist.

Nama-zake (Fresh Sake)

Definition

• Never pasteurized
• Freshest possible state

Characteristics

• Vibrant aroma
• Fresh, lively flavor
• May have slight effervescence
• Requires refrigeration

Risks

• Quality changes quickly
• Temperature control essential
• Short shelf life

Nama-chozo-shu (Fresh-Stored)

Definition

• No pasteurization during storage
• Single pasteurization before shipping

Characteristics

• Retains nama character
• Some stability
• Balance of freshness and preservation

Namazume (Fresh-Bottled)

Definition

• Pasteurized before storage
• No pasteurization at bottling

Characteristics

• Matured flavor
• Fresh at bottling
• “Hiyaoroshi” is the classic example

Hi-ire (Pasteurized)

Definition

• Two pasteurizations
• Most common style

Characteristics

• Stable quality
• Can be stored at room temperature
• Mellow flavor

Styles Through Combination

Muroka Nama Genshu

Processing

• Filtration: None (or minimal)
• Pasteurization: None
• Dilution: None

Characteristics

• Most direct expression of flavor
• Fresh and powerful
• Higher alcohol (17-19%)
• Rich aroma

How to Enjoy

• Well chilled
• Finish soon after opening
• Requires refrigeration

Muroka Nama

Processing

• Filtration: None
• Pasteurization: None
• Dilution: Yes

Characteristics

• Fresh and approachable
• Muroka umami
• Standard alcohol level

Muroka Hi-ire

Processing

• Filtration: None
• Pasteurization: Yes

Characteristics

• Rich umami
• Settled flavor
• Good storage stability

Filtered Nama

Processing

• Filtration: Yes
• Pasteurization: None

Characteristics

• Clear and fresh
• Minimal off-flavors
• Clean taste

Filtered Pasteurized (Standard)

Processing

• Filtration: Yes
• Pasteurization: Yes

Characteristics

• Most stable
• Well-balanced flavor
• Room temperature storage possible

What Is Genshu?

Definition of Genshu

Sake not diluted after pressing.

Standard Sake

• Pressed sake is around 18-20% ABV
• Diluted to 15-16%
• Makes it more approachable

Genshu

• No dilution
• Higher alcohol (17-19%)
• Full-bodied flavor

Characteristics of Genshu

Flavor

• Rich and powerful
• Concentrated umami
• Satisfying body

How to Enjoy

• On the rocks
• Sip slowly in small amounts
• Add ice to adjust yourself

Impact on Flavor

Effects of Filtration

With Filtration

• Clear and transparent
• Fewer off-flavors
• Clean impression
• Tends light and refined

Muroka

• Yellowish tinge
• Rich umami
• Full body
• Complex flavor

Effects of Pasteurization

With Pasteurization

• Settled flavor
• Mellow
• Smoothed edges
• Better preservation

Nama (No Pasteurization)

• Fresh and youthful
• Vibrant aroma
• Sharp impression
• May have slight fizz

Effects of Genshu

With Dilution

• Easy drinking
• Well balanced
• Food-friendly

Genshu

• Full-bodied
• Impactful
• Satisfying in small amounts

Sake and the Seasons

Seasonal Releases

Pasteurization timing creates seasonal sake.

Shiboritate (Winter-Spring)

• Fresh from pressing
• Nama, fresh
• New sake season

Natsu-zake (Summer)

• Designed for summer
• Light, refreshing
• Nama or low-alcohol options

Hiyaoroshi (Autumn)

• Pasteurized in spring, aged through summer
• Released as namazume
• Mellow, deep flavor

Kan-zake (Winter)

• Pasteurized sake is standard
• Enjoyed warmed

The Appeal of Hiyaoroshi

Characteristics

• Sake pressed in spring, aged through summer
• Released as namazume in early autumn
• Mellowness from aging
• Freshness from namazume

Origin of the Name

• “Hiya” (cold) and “orosu” (release/ship)
• Shipped “cold” due to single pasteurization

Storage and Handling

Storing Nama Sake

Essential Conditions

• Refrigeration (below 5°C)
• Avoid direct sunlight
• Consume promptly after opening

Signs of Deterioration

• Change in aroma
• Increased sourness
• Color change

Storing Pasteurized Sake

Conditions

• Cool, dark place
• Room temperature acceptable
• Refrigeration recommended after opening

Relatively Long-Lasting

• About 1 year unopened
• 1-2 weeks after opening

Notes on Muroka

About Lees

• Lees may settle at bottom
• Gently mix before drinking, or enjoy the clear portion
• The lees are part of the umami

Selection Guide

By Preference

Love Fresh Flavors

• Muroka nama
• Nama genshu
• Shiboritate

Love Settled Flavors

• Pasteurized sake
• Hiyaoroshi
• Aged sake

Love Clean Flavors

• Filtered nama
• Honjozo nama

Love Full-Bodied Flavors

• Muroka nama genshu
• Genshu

By Occasion

On Hot Days

• Ice-cold nama
• Clean filtered sake

On Cold Days

• Warm pasteurized junmai
• Lukewarm hiyaoroshi

Special Occasions

• Muroka nama genshu
• Limited nama releases

Reading the Label

Label Patterns

“Muroka Nama Genshu”

• No filtration + No pasteurization + No dilution
• Full specification

“Nama-zake”

• No pasteurization
• Filtration and dilution unspecified

“Namazume” or “Namazume”

• Pasteurized before storage, none at bottling

“Nama-chozo”

• No pasteurization before storage, pasteurized before shipping

“Genshu”

• No dilution
• Pasteurization and filtration unspecified

When Nothing Is Stated

Without specific labels, typically:

• With filtration
• Two pasteurizations
• With dilution

Conclusion

Filtration and pasteurization. These two processes combine to create sake’s diverse styles.

Process	Characteristic
Muroka	Rich umami, full body
Filtered	Clear, clean
Nama	Fresh, vibrant
Pasteurized	Stable, mellow
Genshu	Full-bodied, powerful

No style is inherently “better.” Choose based on the season, the food, your mood.

Look at the label, imagine what processing the sake has undergone, then compare with the actual taste. That’s another way to deeply enjoy sake.

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For more on nama sake, see Nama Sake.

For the science of pasteurization, see The Science of Hi-ire.