Complete Guide to Fermentation Troubleshooting: Scientific Solutions for Common Failures

Making fermented foods is enjoyable, but sometimes things don’t go as planned. “Mold appeared,” “It became too sour,” “Strange smell developed”—these are failures everyone experiences at least once.

However, every failure has a cause. And once you understand the cause, the solution becomes clear. This article explains the common troubleshooting issues for all fermented foods, their scientific causes, and solutions—whether you’re making miso, nukadoko, bread, or yogurt.

Common Causes of Fermentation Failures

Fermentation troubles share common causes regardless of the type of fermented food. Understanding these can help prevent many failures.

1. Temperature Management Failures

Fermentation is driven by microbial activity. Microbial activity is highly dependent on temperature.

When Temperature is Too Low

Microbial activity slows down, and fermentation either doesn’t progress or proceeds very slowly. For example, bread dough won’t rise, or yogurt won’t set.

When Temperature is Too High

Microorganisms die or ferment excessively. Particularly above 60°C (140°F), most fermentation microbes will die. High temperatures can also cause lactic acid bacteria to proliferate excessively, resulting in overly sour flavors.

2. Inappropriate Salt Concentration

Salt is a crucial element that regulates microbial activity. Inappropriate salt concentration can cause fermentation failures.

When Salt is Insufficient

Harmful microorganisms (spoilage bacteria, pathogens) proliferate more easily. Lactic acid bacteria may also proliferate excessively, resulting in overly sour flavors.

When Salt is Excessive

Fermentation microorganisms’ activity is suppressed, and fermentation doesn’t progress. The taste also becomes too salty and unpalatable.

Countermeasures

• Follow the salt concentration specified in recipes
• Measure salt accurately
• Understand that salt concentration varies by salt type (refined salt vs. natural salt)

3. Contamination by Unwanted Microorganisms

Using unclean environments or tools allows contaminants to enter, causing fermentation failures. Contaminants cause putrid odors, discoloration, and mold growth.

Main Causes of Contamination

• Insufficient sterilization of tools
• Inadequate hand washing
• Unsanitary work environment
• Contaminated ingredients

Countermeasures

• Sterilize tools by boiling or with alcohol
• Wash hands thoroughly (with soap for at least 30 seconds)
• Work in a clean environment
• Use fresh ingredients

4. Incorrect Fermentation Time

Fermentation time that is too short or too long causes problems.

When Fermentation Time is Too Short

Fermentation is insufficient, and flavors don’t develop. For example, yogurt won’t set, or bread won’t rise.

When Fermentation Time is Too Long

Over-fermentation causes excessive sourness or strange odors. Particularly when lactic acid bacteria or acetic acid bacteria proliferate excessively, the product becomes too sour.

Countermeasures

• Follow the fermentation time specified in recipes
• Adjust according to temperature and environment
• Observe fermentation progress regularly

Identifying Mold: Edible vs. Dangerous Molds

Mold growth on fermented foods is not uncommon. However, not all molds are dangerous. On the other hand, some molds are harmful, so correct identification is crucial.

Dangerous Molds (Never Consume)

Molds Requiring Caution (Situation-Dependent)

White Mold

White mold treatment varies depending on the fermented food.

• White film on nukadoko (kahm yeast): A type of yeast that is harmless. Remove it and stir, and there’s no problem.
• White mold on miso: If white mold grows thinly on the surface, remove the moldy part and surrounding area deeply, and the rest is edible.
• White mold on cheese: Camembert cheese and similar varieties intentionally use white mold (Penicillium camemberti). This is safe.

What to Do When Mold Appears

For Black, Green, or Pink Mold

Unfortunately, discard it. Mold toxins may have spread to invisible areas.

For White Mold

1. Remove the moldy part and surrounding area deeply (3〜5cm / 1〜2 inches)
2. Check the smell and color of the remaining portion
3. If there are no abnormalities, it’s edible
4. Sprinkle salt on the surface to prevent mold recurrence

Basic Principles for Preventing Troubles

To prevent fermentation troubles, it’s important to follow these basic principles.

1. Maintain a Clean Environment

Keep tools and hands clean to prevent contamination.

• Sterilize tools by boiling or with alcohol
• Wash hands with soap for at least 30 seconds
• Keep work surfaces clean

2. Maintain Strict Temperature Control

Use a thermometer to accurately manage fermentation temperature.

• Understand the optimal temperature for each fermented food
• Measure regularly with a thermometer
• Use refrigeration in summer, warming in winter

3. Follow Recipes

Especially for beginners, following recipes is the shortcut to success.

• Measure ingredient quantities accurately
• Follow salt concentration guidelines
• Follow fermentation times

4. Don’t Neglect Observation

Regularly observe the state of fermented foods and address abnormalities promptly.

• Color changes
• Odor changes
• Texture changes
• Mold appearance

5. Keep Records

Recording temperature, fermentation time, and results leads to improvements next time.

Conclusion

Fermentation troubles always have causes. And once you understand the causes, solutions become clear.

Common Causes of Troubles

• Temperature management failures: Follow optimal temperature for each fermented food
• Inappropriate salt concentration: Follow recipe salt concentration
• Contamination: Use clean environment and tools
• Incorrect fermentation time: Follow recipe times and observe

Identifying Molds

• Black, green, pink molds: Discard
• White mold: Depending on situation, edible after removal
• Cheese molds: Properly managed edible molds are safe

Don’t fear failure—view troubles as “learning opportunities.” Use this article as a reference and enjoy making delicious fermented foods.

---

---