Free Tempeh Starter & Incubation Calculator
Calculate dry soybean yield, lactic/acetic acid dosing for mold inhibition, Rhizopus starter culture weights, and master the two-phase incubation metabolic heat curve.
🌱 Legume Substrate & Batch Size
Cooked Bean Yield: ~1,100 g (Yields ~4 standard tempeh cakes)
• Phase 1 (Hours 0 - 14): Exogenous Heat: Maintain incubator at 86°F - 88°F (30°C - 31°C). The spores germinate and initial white hyphae appear.
• Phase 2 (Hours 14 - 36): Endothermic Self-Heating: Mycelial growth releases intense metabolic heat! Turn down or switch off your external heating pad. Ensure ambient temp stays around 75°F - 80°F so core bean temp does not exceed 100°F (38°C).
The Dryness Rule: Rhizopus mold cannot grow on wet bean surfaces. After draining the boiled beans, dry them completely with a clean towel or hair dryer until the seed skins are totally matte and dry to the touch before inoculating.
Recommended Tools & Equipment
Tested hardware and components for high reliability
The Science of Indonesian Tempeh Fermentation
Tempeh is a traditional solid-state fermentation originating in Central Java. The zygomycete fungus Rhizopus oligosporus (or Rhizopus oryzae) knits split soybeans into a dense, solid white cake through an interconnected network of branching mycelial hyphae.
Why Acidification is Mandatory
Raw soybeans naturally have a neutral pH (~6.5). In warm, moist incubation conditions, dangerous bacteria (such as Bacillus cereus and Staphylococcus aureus) would rapidly outgrow and rot the beans.
Vinegar Rule: Add 25 - 30 mL (2 tbsp) of 5% vinegar per 500g dry soybeans
Rhizopus flourishes in acidic conditions (pH 4.0 to 5.5), while pathogenic bacteria are completely suppressed.
The Metabolic Heat Trap
Between 14 and 24 hours of incubation, rapid fungal metabolism generates significant exothermic heat. The internal temperature of the bean mass can spike 10°F to 15°F above the surrounding air temperature. If the internal core temperature exceeds 104°F (40°C), the mycelium dies and the batch spoils with a black, ammonia-smelling rot.
Frequently Asked Questions
What do grey or black patches on my finished tempeh mean?
Grey or black spots are harmless Rhizopus sporulation (the mold producing spores), typically occurring near air holes where oxygen is abundant. It is completely safe and normal. However, if the beans are slimy, pink, or smell pungent like ammonia, discard the batch.
Do I have to dehull the soybeans?
Yes! The impermeable seed coats (hulls) prevent the mold hyphae from penetrating the nutrient-rich bean cotyledons. Split dehulled soybeans allow the fungal mycelium to bind the beans into a solid, sliceable cake.
Can I freeze finished tempeh?
Yes! Once the tempeh cake is fully covered in dense white mycelium (usually 24 to 36 hours), steam it for 10 minutes to halt fermentation, cool, and freeze for up to 6 months.