Tempeh Fermentation Calculator
Calculate soybean quantities, incubation time, and temperature settings for homemade tempeh batches.
Tempeh is made by fermenting cooked, dehulled soybeans with Rhizopus oligosporus mold. The mycelium binds the beans into a firm, sliceable cake. Successful tempeh depends on precise temperature control and proper inoculation rates.
Yield Formula: Finished Tempeh Weight ≈ Dry Soybean Weight × 2.2
Soybeans roughly double in weight when soaked and cooked. The fermentation process adds minimal weight (mycelium growth), so 500 g dry soybeans yields approximately 1,100 g (2.4 lb) of finished tempeh.
Starter Culture (Inoculation Rate): Standard rate: 1 teaspoon (about 2 g) of tempeh starter per 500 g dry soybeans. Formula: Starter (g) = (Dry Soybeans in grams / 500) × 2
Process Timeline:
| Step | Duration | Temperature |
|---|---|---|
| Soaking | 8–12 hours | Room temp |
| Cooking (boil) | 30–45 minutes | 212°F (100°C) |
| Drying and cooling | 30–60 minutes | Cool to 95°F (35°C) |
| Inoculation | 5 minutes | Below 95°F (35°C) |
| Incubation | 24–48 hours | 85–90°F (29–32°C) |
Critical Temperature Ranges:
- Below 77°F (25°C): fermentation stalls, bacteria may dominate
- 85–90°F (29–32°C): optimal mycelium growth
- Above 95°F (35°C): starter culture dies, fermentation fails
- At 88°F (31°C), incubation typically completes in 30–36 hours
Worked Example — 1 kg batch:
- Dry soybeans: 1000 g
- Soaking: 8 hours minimum (beans swell to ~2000 g)
- Starter needed: (1000 / 500) × 2 = 4 g (2 teaspoons)
- Cooking: 40 minutes at full boil
- Incubation at 88°F: approximately 32 hours
- Expected yield: ~2,200 g finished tempeh
Vinegar Addition: Add 1 tablespoon (15 ml) of white vinegar per 500 g dry beans to the cooked beans before inoculation. This lowers pH to 4.5–5.0, inhibiting bacterial contamination while supporting Rhizopus growth.
Packaging: Perforate ziplock bags or banana leaves with holes every 1 inch (2.5 cm) for air exchange. The mold needs oxygen to grow but excessive airflow dries the surface.