Knowledge Base

Tempeh

Legume ferment · Traditional · peer-reviewed

Indonesian soybean cake bound into a firm slab by a living mould — a mould ferment, not a bacterial one, and a genuinely complete plant protein.

Advanced to make
1–2 days ferment
protein, live-cultures, b-vitamins supplied

Ingredients

  • Dry soybeans (dehulled)300 g
  • Vinegar (to acidify the soak)1 tbsp
  • Tempeh starter (Rhizopus oligosporus spores)1 tsp

How to make it

  1. Step 1

    Soak dehulled beans overnight with a splash of vinegar to acidify (pH < 5).

  2. Step 2

    Cook until just tender, then drain and dry the beans thoroughly — surface moisture ruins the ferment.

  3. Step 3

    Cool to body temperature and mix in the Rhizopus starter evenly.

  4. Step 4

    Press into a perforated bag or box, ~2 cm thick, so the mould can breathe.

  5. Step 5

    Incubate at 30–32 °C for 24–48 h.

  6. Step 6

    Done when white mycelium fully binds the beans into a firm cake. Refrigerate or cook.

What it is

Tempeh is a mould-fermented soybean cake from Indonesia. Unlike the bacterial ferments on this shelf, tempeh is made by a filamentous fungus, Rhizopus oligosporus (and related Rhizopus species), whose white mycelium grows through cooked beans and knits them into a sliceable slab with a nutty, mushroom-like flavour.

The science

The mould does more than bind the beans. During the 24–48 h ferment Rhizopus secretes enzymes that partially digest proteins, lipids and phytate, improving digestibility and freeing minerals; it also raises levels of some B-vitamins and produces antioxidant isoflavone aglycones (Nout & Kiers, 2005). A comprehensive review documents tempeh's protein quality, safety controls and health effects (Ahnan-Winarno et al., 2021).

Safety

Two controls matter. Acidify the soak (vinegar or a lactic pre-ferment to pH below ~5) so bacteria like Bacillus can't outcompete the mould, and incubate warm and aerated at 30–32 °C. Some grey-black patches of sporulation around the edges are normal and harmless. Discard if the cake smells of ammonia (over-fermented) or shows fuzzy coloured (non-Rhizopus) mould.

Signs it worked / troubleshooting

  • ✅ Good: solid white cake, sweet mushroomy smell, holds together when sliced.
  • ⚠️ Patchy binding = beans too wet, too cool, or packed too thick → dry beans better, hold 31 °C, thin the slab.
  • 🚫 Ammonia reek or slimy = over-fermented or contaminated → discard.

How to store

Refrigerate up to a week, or freeze. Always cook tempeh before eating — steam, fry or bake.

References

  • Nout MJR, Kiers JL (2005). Tempe fermentation, innovation and functionality: update into the third millennium. Journal of Applied Microbiology 98(4):789–805. doi:10.1111/j.1365-2672.2004.02471.x
  • Ahnan-Winarno AD, Cordeiro L, Winarno FG, Gibbons J, Xiao H (2021). Tempeh: A semicentennial review on its health benefits, fermentation, safety, processing, sustainability, and affordability. Comprehensive Reviews in Food Science and Food Safety 20(2):1717–1767. doi:10.1111/1541-4337.12710

Related

YogurtSauerkraut