5 Solutions for Nukadoko Problems: Fixing Sour, Watery, and Moldy Issues
“My nukadoko has become too sour,” “White mold-like stuff is growing,” “It smells weird”… When managing a nukadoko (rice bran pickling bed), you may encounter these troubles. But don’t worry.
This article explains common nukadoko problems, their causes, and scientifically-based solutions in detail. Once you understand how microorganisms work, troubles won’t be scary anymore.
The Root Cause of Nukadoko Problems: When Microbial Balance Collapses
Most nukadoko problems are caused by disrupted microbial balance. Microorganisms such as lactic acid bacteria, yeast, and butyric acid bacteria coexist in the proper environment, but when conditions like temperature, salt content, moisture, and oxygen change, the balance collapses.
When trouble occurs, the first step to solving it is to think, “What caused the microbial balance to collapse?”
My Failure Experience
I once left my nukadoko at room temperature during summer, and it became so sour that it was inedible. The temperature was too high, causing lactic acid bacteria to multiply excessively. After adding salt and managing it in the refrigerator, it returned to normal within a week.
Problem 1: Too Sour
Cause
Lactic acid bacteria have multiplied excessively, producing too much lactic acid. This occurs due to high temperature, insufficient stirring, or low salt content.
Scientific Background
Lactic acid bacteria are most active at 25-30°C (77-86°F). If you leave nukadoko in a warm place during summer, lactic acid bacteria rapidly multiply, and the pH can drop below 4.0. This excessive acidity makes the pickles too sour.
Solutions
| Solution | Effect | How to Implement |
|---|---|---|
| Add salt | Suppresses lactic acid bacteria activity | Add 1-2 tablespoons and mix well |
| Increase stirring frequency | Activates yeast by supplying oxygen | Stir twice a day, mixing from the bottom |
| Add eggshells | Calcium neutralizes acid | Wash, dry, crush, and add shells |
| Store in refrigerator | Slows fermentation rate | Store at 10-15°C (50-59°F) |
Prevention Tip
During summer, storing in the refrigerator is recommended. Fermentation slows down, preventing excessive sourness. However, when refrigerated, stirring frequency can be reduced to once every 2-3 days.
Problem 2: Too Watery
Cause
Too much water has been released from vegetables, or you’ve pickled too many high-moisture vegetables (cucumbers, tomatoes, etc.).
Scientific Background
When you pickle vegetables, osmotic pressure causes moisture from the vegetables to move into the nukadoko. Excessive moisture dilutes the salt concentration, making it easier for harmful bacteria to proliferate. Microbial activity also decreases.
Solutions
- Absorb moisture with paper towels: Place paper towels on the surface of the nukadoko to absorb excess moisture
- Add rice bran: Add 50-100g of rice bran to adjust the consistency
- Reduce high-moisture vegetables: Avoid pickling too many tomatoes, cucumbers, etc.
- Add salt: Maintain salt concentration at 10-13%
Warning
If you leave watery nukadoko unattended, harmful bacteria can proliferate and cause strange odors. Address it promptly.
Problem 3: White Mold (Film-Forming Yeast) Has Grown
Cause
A white film-like substance on the surface is film-forming yeast that has proliferated. This occurs due to insufficient stirring or low salt content.
Scientific Background
Film-forming yeast (such as Pichia species) are oxygen-loving microorganisms that proliferate on the surface of nukadoko. They are harmless, but if they multiply excessively, the flavor can deteriorate.
Solutions
- Remove the white part: Scoop out the white film with a spoon
- Add salt: Add about 1 tablespoon
- Stir thoroughly every day: Mix by scooping up from the bottom
- Wipe the container edges: Wipe off any bran stuck to the container edges with a clean cloth
Film-Forming Yeast is Harmless
Although it looks like white mold, film-forming yeast is harmless. Remove it and add salt, and it will return to normal immediately. However, blue or black mold is harmful, so if it spreads widely, remake your nukadoko.
Problem 4: Strange Smell
Cause
Harmful bacteria proliferation, residual old vegetables, or excessive butyric acid bacteria growth.
Scientific Background
At the bottom of nukadoko, where oxygen is scarce, butyric acid bacteria are active. While butyric acid bacteria have health benefits, excessive growth can produce a “sweaty feet-like smell.”
Types of Smells and Solutions
| Smell Type | Cause | Solution |
|---|---|---|
| Sour smell | Excessive lactic acid bacteria | Add salt, increase stirring frequency |
| Alcohol smell | Excessive yeast | Stir to supply oxygen, add salt |
| Sweaty feet smell | Excessive butyric acid bacteria | Stir thoroughly, add mustard powder |
| Rotten smell | Harmful bacteria proliferation | Remove old vegetables, add salt, remake if necessary |
Effect of Mustard Powder
Adding mustard powder (about 1 teaspoon) has a sterilizing effect and can suppress strange smells. The component allyl isothiocyanate in mustard inhibits harmful bacteria proliferation.
Problem 5: Pickles Don’t Taste Good
Cause
Immature nukadoko, improper salt concentration, or pickling time that’s too short or too long.
Solutions
- Develop your nukadoko: Newly made nukadoko needs 2-3 weeks to increase microorganisms
- Check salt concentration: 10-13% is ideal. Using a salt concentration meter gives accurate measurements
- Adjust pickling time: Cucumbers: 12-18 hours, daikon radish: 24-36 hours as a guideline
- Continue “discard pickling”: For the first 1-2 weeks, continue discard pickling with cabbage outer leaves, etc.
Conditions for Delicious Nukadoko
- pH 4.0-4.5 (weakly acidic)
- Salt concentration 10-13%
- Temperature 20-25°C (68-77°F)
- Moderate moisture (miso-like consistency)
Daily Management for Trouble Prevention
Daily management is important to prevent troubles before they occur.
Daily Checkpoints
| Check Item | Ideal State | State Requiring Action |
|---|---|---|
| Smell | Subtle acidity and rice bran aroma | Strong sour smell, alcohol smell, rotten smell |
| Consistency | Miso-like consistency | Watery, too firm |
| Surface | Flat and uniform | White film, mold |
| Color | Light brown to brown | Darkened, greenish |
Summary
Nukadoko problems occur when microbial balance collapses. But if you understand the causes and respond appropriately, most problems can be solved.
Key Points from This Article:
- If too sour: Add salt, increase stirring frequency, store in refrigerator
- If too watery: Absorb moisture with paper towels, add rice bran
- If white mold grows: Remove it and add salt, stir daily
- If strange smell: Add salt and mustard powder, stir thoroughly
- If pickles don’t taste good: Develop nukadoko, adjust salt concentration and pickling time
Nukadoko management becomes easier once you understand the microbial ecosystem. Don’t be afraid of troubles—they’re opportunities to learn about microorganisms!
References
- Koizumi, T. (2017). Fermented Foods. Chuo Koron Shinsha.
- Maehashi, K. (2019). Understanding Fermented Foods: The Science Behind Them. Gijutsu-Hyoron Co.
- Brewing Society of Japan. (2018). “Microbial Ecology of Nukadoko.” Journal of the Brewing Society of Japan, 113(5), 301-310.
- Tokyo University of Agriculture, Faculty of Applied Bioscience. (2019). “Lactic Acid Fermentation and pH Control in Nukadoko.” Research Report of Faculty of Applied Bioscience.
- Kobayashi, M. (2020). “Diversity and Function of Microorganisms in Traditional Fermented Foods.” Japanese Journal of Lactic Acid Bacteria, 31(2), 89-97.
- Ministry of Agriculture, Forestry and Fisheries. (2020). “Traditional Japanese Fermented Foods and Microbial Culture.”
