How to Make Soybean oil cake
Soybean oil cake (specifically the byproduct of traditional hydraulic or expeller pressing) undergoes alkaline fermentation, a process driven primarily by Bacillus subtilis. Unlike lactic acid fermentation, this process increases the pH of the substrate. The result is a pungent, umami-rich condiment similar to Kinema or Thua Nao, where proteins are broken down into peptides and amino acids, often accompanied by a characteristic ammonia aroma and mucilaginous texture.
Category: Legumes & Soy · Method: Alkaline · Time: 2-5d · Difficulty: 3/5 · Yield: varies · Temp: 30-40°C
History
This byproduct fermentation originated in China as a way to utilize all parts of the soybean. The alkaline fermentation breaks down proteins into savory amino acids, creating an intense seasoning paste.
Ingredients
- 500g Soybean oil cake (pressed residue) — Use oil-pressed cake rather than tofu okara; if using okara, it must be pressed extremely dry and steamed to reduce moisture to approx 50-60%.
- As needed Bacillus subtilis source — Either commercial Natto starter or clean, dried rice straw/banana leaves which naturally host wild Bacillus.
- 25-50g Salt (Post-fermentation) — Added ONLY after the 2-5 day fermentation is complete to stabilize the product.
Equipment
- Fermentation vessel
- Wrapping material
- Warm fermentation area (30-40°C)
Instructions
Hydration and Sterilization
If using dry oil cake, hydrate slightly until it can be formed. Steam the cake for 45-60 minutes. This is a critical safety step to eliminate competing pathogens (like B. cereus) in this high-protein, low-acid environment.
Time: 1 hour
Tip: The cake should be soft enough to pinch but not mushy.
Inoculation
Allow the cake to cool to 40-45°C. Mix in starter culture or layer the warm cake with cleaned rice straw. The heat triggers the germination of Bacillus spores while preventing the growth of heat-sensitive spoilage bacteria.
Time: 15 min
Tip: Do not add salt at this stage; salt inhibits the growth of the necessary Bacillus bacteria.
Incubation and Humidity Control
Place in a fermentation chamber at 30-40°C with high humidity (80-90%). The cake must be kept in a thick layer (2-4cm) to allow the bacteria to generate its own metabolic heat.
Time: 2-5 days
Tip: Monitor the smell; a faint ammonia scent is normal, but a putrid 'rotten egg' smell indicates failure.
Salting and Stabilization
Once the cake is covered in a white/grey biofilm and becomes sticky/stringy, mix in the salt. The salt, combined with the high pH generated by the fermentation, now acts as a preservative.
Time: 20 min
Tip: This stops the Bacillus activity and prevents the ammonia scent from becoming overwhelming.
Drying and Aging
Flatten the fermented paste into discs or small nuggets and sun-dry or dehydrate at low heat until firm. This develops the final deep umami profile.
Time: 2-7 days
Tip: Properly dried cakes can be stored for long periods without refrigeration.
Fermentation Timeline
- Day 1-2: Bacterial growth begins — Ammonia smell develops as proteins break down.
- Day 3-4: Full fermentation — Sticky, stringy texture develops.
- Day 5+: Drying phase — Flavor concentrates as moisture evaporates.
Signs of Success & Spoilage
Good signs
- Ammonia-like smell (normal)
- Sticky texture
- Brown coloration
- Umami-rich taste
Warning signs
- Green or black mold
- Putrid smell
- Slimy breakdown
- Insect infestation
Troubleshooting
- No 'strings' or mucilage forming
- Cause: Temperature too low or salt added too early. Solution: Ensure incubation stays above 30°C and never salt the substrate before the Bacillus has colonized.
- Putrid or foul odor (not ammonia)
- Cause: Contamination due to insufficient steaming or excess moisture. Solution: Discard the batch. Ensure a full 60-minute steam and check that the cake isn't sitting in standing water.
- Excessive ammonia smell
- Cause: Fermentation went too long or temperature was too high. Solution: Move to the drying/salting phase immediately. In the future, check the specimen 12 hours earlier.
Storage
Dried at room temperature or refrigerated Keeps Several months to a year. Keep dry to prevent mold after fermentation.
Health Benefits
- High protein content
- B vitamins from fermentation
- Umami compounds
- Fiber from soybean residue
Serving Suggestions
- Crumbled into stir-fries
- As seasoning base
- In soup stocks
- With rice dishes
Related Legumes & Soy Ferments
Other Alkaline Ferments
- Hákarl — Fish & Seafood
- Century egg — Eggs
- Dawa-dawa (African locust) — Nuts & Seeds
- Ogiri (melon seed) — Nuts & Seeds