Making tempeh at home is a rewarding fermentation process that produces a nutrient-dense, protein-rich food with superior flavor compared to store-bought versions. This traditional Indonesian fermented soybean product requires minimal ingredients but careful attention to temperature and timing during the 24-48 hour fermentation process.

Essential Ingredients

Basic Recipe (Makes 1 Block)

• 500g organic soybeans (preferably non-GMO for best flavor and texture)
• 1 heaped teaspoon tempeh starter culture (Rhizopus oligosporus)
• 3 tablespoons brown rice vinegar (or white vinegar)
• 2 liters water for soaking and cooking

Alternative Ingredients

• 2-3 grams tempeh starter per kilogram of soybeans as general guideline
• Any legumes can substitute soybeans (chickpeas, black beans, etc.)

Required Equipment

Essential Tools

• Large bowl for soaking beans
• Pressure cooker or large pot for cooking
• Colander for draining
• Clean kitchen towels
• Gallon-size ziplock bags
• Toothpicks for creating air holes
• Wire rack for incubation

Temperature Control Equipment

• Thermometer to monitor temperature
• Incubation setup – options include:
  • Dehydrator set to 85-91°F (29-33°C)
  • Oven with light on
  • Styrofoam cooler with warm water bottles
  • Reptile heating mat with towel cover

Step-by-Step Instructions

Day 1: Preparation (25 minutes active time)

Step 1: Soak the Soybeans

Soak 500g soybeans in 2 liters of water overnight or minimum 12 hours. The beans will expand significantly during soaking6.

Step 2: Remove Skins and Split Beans

Rub soybeans between your hands under running water to remove skins and split the beans in half. Agitate the water to help skins float to the surface, then pour them off through a colander. Repeat this process until most skins are removed – some whole beans and remaining skin are acceptable.

Step 3: Cook the Soybeans

• Pressure cooker method: Cook soybeans with 2 liters water for 12 minutes until tender but not mushy
• Stovetop method: Boil on medium-low heat for 45 minutes to 1 hour, skimming foam regularly

The beans should be soft but maintain their shape – avoid overcooking as this affects texture.

Step 4: Drain and Cool

Drain the cooking water completely and spread soybeans on a tray lined with clean kitchen towels. Allow beans to steam dry and cool completely to room temperature – this is crucial as hot beans will kill the starter culture.

Step 5: Add Vinegar and Starter

Once beans are completely cool to touch, place in a clean large bowl. Add 3 tablespoons brown rice vinegar and mix well – the acid helps create optimal fermentation conditions. Sprinkle 1 heaped teaspoon tempeh starter evenly over beans and mix thoroughly to distribute the culture.

Step 6: Package for Fermentation

Transfer the inoculated beans into a gallon-size ziplock bag. Press out all air and seal, then flatten the beans into an even layer about 2.5-4cm thick. Use a chopping board to help create an even, flat surface.

Step 7: Create Ventilation Holes

Using a toothpick, prick holes throughout the entire bag, spacing them 1-2 inches apart. Flip the bag and repeat on the other side – proper ventilation is essential for healthy fermentation.

Day 2-3: Fermentation (48 hours passive time)

Step 8: Incubate

Place the bag on a wire rack in a warm, well-ventilated location maintaining 85-91°F (29-33°C). The ideal temperature range is 30-38°C according to research sources. Maintain relative humidity between 75-85% if possible.

Step 9: Monitor Progress

• 12 hours: White fuzzy growth (mycelium) begins appearing
• 24 hours: White mold covers most of the surface
• 36-48 hours: Complete fermentation with solid white cake

Important: After 12 hours, the tempeh generates its own heat, so reduce or eliminate external heat sources to prevent overheating.

Step 10: Check for Completion

Tempeh is ready when the entire bag feels solid and all gaps are filled with white mycelium. It should have a pleasant, nutty, mushroom-like aroma. The fermentation time varies based on ambient temperature – warmer conditions speed the process.

Safety and Quality Control

Normal Characteristics

• Gray or black spots are completely normal – these are mature spores and are safe to eat
• Pleasant nutty, mushroom-like smell indicates healthy fermentation
• Firm, solid texture throughout the block

Warning Signs – Discard If Present

• Green or pink mold anywhere on the tempeh
• Strong ammonia smell indicating contamination
• Slimy, mushy texture from overheating during fermentation
• Unpleasant odors other than the characteristic nutty aroma

Storage and Preservation

Refrigeration

Store finished tempeh in the refrigerator for up to 4 days. The fermentation continues slowly in cold temperatures, gradually intensifying the flavor. Keep in airtight containers at 2-6°C (35-43°F).

Freezing

For longer storage, freeze tempeh for up to 3 months. Cut into desired portions before freezing for convenient use.

Usage Tips

To remove any bitter taste, soak sliced tempeh in warm salted water for 30 minutes before cooking. This also helps the tempeh absorb marinades better.

Troubleshooting Common Issues

Temperature Problems

If fermentation is too slow, increase incubation temperature gradually. If black mold appears extensively, the temperature may be too high – reduce heat and ensure proper ventilation.

Contamination Prevention

Maintain strict hygiene throughout the process. Use clean utensils and containers, and ensure beans are completely cooled before adding starter culture.

Alternative Methods

For those without access to commercial starter, tempeh can be made using rice flour as a fermentation medium, though results may vary.

Where to Source Tempeh Starter

Tempeh starter (Rhizopus oligosporus) is available from:

• Online suppliers like Cultures for Health, Gem Cultures
• Specialty fermentation supply companies
• Etsy and other online marketplaces

Approximately 1/2 teaspoon starter is sufficient for 1kg of soybeans, making small quantities very economical.

Conclusion

Homemade tempeh offers superior flavor, complete control over ingredients, and significant cost savings compared to commercial varieties. While the process requires patience during the 48-hour fermentation period, the active preparation time is minimal. Success depends primarily on maintaining proper temperature, ensuring cleanliness, and allowing adequate fermentation time. The resulting tempeh provides exceptional nutritional value with complete protein profiles and beneficial probiotics from the fermentation process.