Fermented foods are “living foods.” Miso, nukadoko, natto, yogurt, cheese—these foods contain various living microorganisms such as lactic acid bacteria, yeasts, koji molds, and natto bacteria. And microbial activity continues even during storage.
By understanding proper storage methods, you can enjoy fermented foods deliciously and safely. This article scientifically explains the basic principles of storage common to all fermented foods from the perspective of microbial activity.
Specific Storage Methods in Dedicated Articles
This article explains the basic storage principles common to all fermented foods. For detailed storage methods of specific fermented foods (miso, nukadoko, natto, etc.), please refer to their dedicated articles.
Basic Principles of Fermented Food Storage
The most important aspect of fermented food storage is controlling microbial activity. Once you understand microbial activity, appropriate storage methods become clear.
Fermentation Continues After Storage
In fermented foods, microbial activity continues after production. In other words, fermentation progresses even during storage.
- Miso: Aging progresses, color darkens, and flavor changes
- Nukadoko: Balance of lactic acid bacteria and yeasts changes, altering flavor
- Natto: Natto bacteria activity continues, ammonia smell intensifies
- Yogurt: Lactic acid bacteria activity continues, sourness increases
- Cheese: Aging progresses, flavor changes
The purpose of storage is to appropriately control microbial activity and maintain quality.
Temperature Management is Most Important
Microbial activity depends greatly on temperature. By managing temperature appropriately, you can control the rate of fermentation progress.
| Storage Method | Temperature | Microbial Activity | Fermentation Progress | Suitable Use |
|---|---|---|---|---|
| Room Temperature | 59〜77°F (15〜25°C) | Active | Fast | Fermenting products |
| Refrigeration | 41〜50°F (5〜10°C) | Slow | Slow | Finished products |
| Freezing | 0°F (-18°C) or below | Nearly stopped | Nearly stopped | Long-term storage |
Temperature and Microorganisms
Microbial activity approximately doubles for every 10°C (18°F) increase in temperature. Conversely, activity is halved for every 10°C decrease. This property can be used to control fermentation progress rate.
Using Room Temperature, Refrigeration, and Freezing
Storage methods for fermented foods should be chosen based on the product’s state and purpose.
When Room Temperature Storage is Appropriate
Purpose: To advance fermentation, to age
Suitable Fermented Foods
- Miso during aging
- Nukadoko in use
- Fermenting bread dough
- Cheese during aging
Precautions
- If temperature is too high, microorganisms proliferate excessively and quality deteriorates
- Switch to refrigeration during summer
- Observe regularly and check for mold or discoloration
When Refrigeration is Appropriate
Purpose: To slow fermentation progress and maintain quality
Suitable Fermented Foods
- Finished miso
- Natto
- Yogurt
- Cheese
- Kimchi
Precautions
- Even with refrigeration, fermentation slowly progresses
- Consume soon after opening
- Keep containers clean
When Freezing is Appropriate
Purpose: For long-term storage, to completely stop fermentation
Suitable Fermented Foods
- Miso (long-term storage)
- Nukadoko (dormancy)
- Natto
- Bread
Precautions
- Freezing nearly stops microbial activity but doesn’t kill microorganisms
- After thawing, microorganisms resume activity
- Some fermented foods change texture (yogurt, cheese, etc.)
My Failure Story
I once froze yogurt for storage. After thawing, the texture became grainy and couldn’t be eaten as is. However, it was fine when used in smoothies. I learned that some fermented foods are suitable for freezing while others are not.
Container Selection and Management
Choosing appropriate containers is important for storing fermented foods.
Container Materials
| Material | Advantages | Disadvantages | Suitable Fermented Foods |
|---|---|---|---|
| Glass | No odor transfer, clean, transparent to see contents | Heavy, fragile | Miso, nukadoko, yogurt |
| Enamel | No odor transfer, acid-resistant, easy maintenance | Somewhat expensive | Miso, nukadoko, kimchi |
| Ceramic | Good breathability, gradual temperature changes | Heavy, fragile | Miso, nukadoko |
| Plastic | Lightweight, inexpensive, durable | Odor transfer, degrades easily | Natto, yogurt |
Container Management
Keep Clean
- Sterilize with boiling water or alcohol before use
- Wash well and dry after use
- Replace containers periodically
Seal Level
- Ideally not completely airtight, but with moderate breathability
- However, for refrigeration/freezing, use highly sealed containers
Difference Between Best Before Date and Expiration Date
Fermented food packages display either “best before date” or “expiration date.” Understanding the difference between these two is important.
Best Before Date
Definition: The date until which the product can be eaten deliciously
Meaning: Even after this date passes, it doesn’t immediately become inedible. However, flavor and quality may decline.
Applicable Fermented Foods: Miso, natto, yogurt, cheese, etc.
Expiration Date
Definition: The date until which the product can be safely eaten
Meaning: After this date, the risk of food poisoning increases. Consumption within the date is recommended.
Applicable Foods: Fresh foods, bento boxes, etc. (rarely applicable to fermented foods)
| Item | Best Before Date | Expiration Date |
|---|---|---|
| Meaning | Date until delicious | Date until safe |
| After Date | Edible but flavor declines | Better not to eat |
| Target Foods | High-preservation foods | Low-preservation foods |
Edible After Best Before Date?
Fermented foods don’t immediately become inedible after the best before date. However, pay attention to the following points.
Signs It’s Safe to Eat
- Normal smell (fermentation odor present but no putrid smell)
- Normal color (some discoloration is fine)
- No mold growth
- Normal taste (some increase in sourness is fine)
Signs You Shouldn’t Eat
- Putrid smell
- Black or green mold growth
- Stringy texture (except natto)
- Obviously strange taste
Understanding Quality Changes During Storage
Fermented foods undergo quality changes during storage. Understanding these changes enables appropriate judgment.
Normal Changes
Color Changes
Miso becoming darker, yogurt becoming yellowish—these color changes are normal phenomena. This is due to Maillard reactions and oxidation, and is safe to eat.
Increased Sourness
When lactic acid bacteria are active, lactic acid increases and sourness intensifies. This is normal fermentation progress.
Liquid Separation
Whey in yogurt, tamari (liquid) in miso—liquid separation sometimes occurs. This is a normal phenomenon and can be mixed back in for consumption.
Abnormal Changes
Mold Growth
Black or green mold is harmful. If it spreads extensively, disposal is recommended. White mold judgment varies by fermented food type. For details, see Fermentation Troubleshooting.
Putrid Smell
If there’s a clearly unpleasant smell different from fermentation odor, harmful bacteria may be proliferating. Disposal is recommended.
Stringy Texture (Except Natto)
If fermented foods other than natto become stringy, harmful bacteria (especially Bacillus genus bacteria) may be proliferating. Disposal is recommended.
Summary
The key to storing fermented foods is controlling microbial activity. Through temperature management, container selection, and understanding best before dates, you can enjoy fermented foods deliciously and safely.
Key Points from This Article
- Fermentation continues after storage: Controlling microbial activity is important
- Temperature management is most important: Use room temperature, refrigeration, and freezing appropriately
- Container selection matters: Materials have different suitabilities
- Best before date is a guideline: Judge by smell, color, and taste
- Distinguish normal from abnormal changes: Watch for mold, putrid smell, stringiness
Storage Methods for Specific Fermented Foods
For detailed storage methods of each fermented food, please refer to the following dedicated articles.
References
- Koizumi, T. (2018). “Fermentation.” Chuko Shinsho.
- Ishikawa, S. (2020). “The Science of Fermentation.” Kodansha Blue Backs.
- Ministry of Agriculture, Forestry and Fisheries, Japan (2021). “Food Storage Methods and Best Before Dates.”
- Japanese Society for Food Microbiology (2020). “Fundamentals of Food Microbiology.” Kodansha Scientific.
- Ministry of Health, Labour and Welfare, Japan (2021). “Designation of Food Additives Based on Food Sanitation Act.”
