How to make tempeh at home

Tempeh is a compact white cake of dehulled, cooked soybeans bound together by Rhizopus mould. ⁵ It is a controlled mould fermentation, so the starter, the acidity of the beans and the temperature all matter. ⁶ Tempeh is always cooked before eating. ¹

You need

• Dry soybeans, dehulled (split), or whole beans you dehull after soaking ¹
• Tempeh starter (Rhizopus spores) from a reputable supplier, at the dose on its pack ⁵⁷
• Food-grade lactic acid, to bring the beans to pH 4.8 or lower ²

Equipment

• Large pan and colander
• pH strips or a pH meter
• Perforated food bags, or trays with a perforated cover
• An incubator or warm box that holds 25–30 °C, with a thermometer ¹

Method

1. Soak

   Soak the dehulled beans for 6–24 hours, then discard the soaking water. Do not reuse soak water from an earlier batch. ¹²

2. Cook

   Cook the beans in fresh water for 20–30 minutes, then drain and discard the cooking water. ¹

3. Acidify

   Before inoculating, the beans should be at pH 4.8 or lower: add food-grade lactic acid and check with strips or a meter. In tests, lactic acid at this pH controlled Bacillus cereus while vinegar (acetic acid) did not, and unacidified beans fermented poorly. Producers add the acid during soaking or cooking. ²¹

4. Dry and cool

   Spread the hot beans out so that surface water steams off; free water encourages spoilage. Cool them to 20–25 °C (68–77 °F). ¹

5. Inoculate

   Mix the starter in evenly at the dose on its pack. Too little gives patchy growth and more spoilage; too much makes the batch run hot. ¹

6. Pack

   Fill perforated bags or containers in a layer 3–5 cm deep, with small, evenly spaced holes: the mould needs some air, but a thicker layer starves the centre. ¹

7. Incubate

   Keep at 30 °C (86 °F) for 24–36 hours, or at 25 °C (77 °F) for 48–72 hours. Once white growth shows, the beans make their own heat and can reach 40–50 °C, too hot for the mould: lower the setting, space the packs apart and let air move. ¹³

8. Chill, then cook

   As soon as the cake is ready, refrigerate it at 4 °C (40 °F) or below, or freeze it at −18 °C (0 °F). Always cook tempeh before eating. ⁴¹

How to tell it is ready

• The beans are completely covered in white mycelium and bound into a firm cake that does not fall apart when cut ⁵³
• It smells fresh and mushroom-like, with no ammonia ⁵
• It is creamy white; a few grey or black spots near the air holes are spores and acceptable in small amounts ¹

Storing it

• Fresh tempeh is perishable: refrigerate at 4 °C (40 °F) or below as soon as it is ready ¹⁴
• Freeze it at −18 °C (0 °F) for longer keeping ⁸⁴
• We have not found a primary source for how many days home tempeh keeps in the fridge. Cook it soon; if in doubt, throw it out.

And miso?

Miso is a longer project: koji (rice or barley grown with Aspergillus oryzae), cooked soybeans and salt mature together for months. Miso usually holds 11–13% salt, within a range of 5–13%, and matures at 25–30 °C for one month to several years; the salt holds back unwanted microbes and steers the fermentation. More koji makes a sweeter miso. ⁹ We have not found a primary source for tested home proportions or for handling surface growth on home miso, so we do not publish a home miso method yet. Tempeh takes days rather than months and is the better first project.