Fermenting Natto and Tempeh
Natto and tempeh are both traditional foods made by fermenting soybeans with specific cultures — making them at home requires precise control of the culture, temperature, and humidity, making it an advanced challenge for fermentation enthusiasts.
Why It Works
Natto relies on Bacillus subtilis var. natto breaking down soy protein in a warm, humid environment to produce its signature sticky strands and distinctive flavor. Tempeh relies on Rhizopus oligosporus mold forming a dense white mycelium network over the soybeans, binding them into a firm cake. Both require a strictly maintained fermentation temperature.
Steps
- Soak the soybeans, then steam or boil them until soft (for tempeh, remove the skins first). 2. Once the beans have cooled to around 40°C (104°F), inoculate them with natto or tempeh starter culture and mix thoroughly. 3. Spread the beans in a shallow tray or dedicated fermentation container and hold them at a steady 40°C (natto ferments for about 24 hours, tempeh for about 24–48 hours). 4. After fermentation, natto develops better flavor if refrigerated to mature for a day; tempeh can go straight into the fridge.
Key Points
A fermentation box or a yogurt maker with a warming function is a practical tool for maintaining steady temperature at home. Sterilize all fermentation containers and tools thoroughly, since contamination from stray bacteria can ruin the batch or produce off odors.
Common Questions
If large black or gray spots appear during tempeh fermentation, accompanied by a strong ammonia or rotten smell, the batch has been contaminated and the entire batch should be discarded rather than eaten. Properly fermented tempeh should be evenly covered in white mycelium with a mild, nutty, mushroom-like aroma.
Tips
Without a dedicated fermentation box, households can improvise by using an insulated cooler with a hot water bottle, or an oven's proofing function to maintain a steady temperature — just check the temperature periodically and refresh the heat source as needed.
