Fermentationist
Fix / Tempeh

Troubleshooting · New on 9 October 2026

Tempeh problems and fixes

Loose beans, slime, ammonia, black spots or an overheating batch: what each sign means and when tempeh must be thrown out.

The methodRecord the batch

Good tempeh is a firm white cake with a fresh smell and no ammonia. 2 Growth problems usually trace back to air, temperature, starter dose or the acidity of the beans; slime, ammonia and coloured mould mean the batch is discarded.

Beans not bound, patchy growth

Likely causes

  • Too little starter, or starter not mixed in evenly 4
  • Layer too thick, so the centre runs short of air 4
  • Holes too few or too small 4
  • Beans not acidified 1

What to do

  • Use the dose on the starter pack and mix thoroughly 4
  • Pack 3–5 cm deep with evenly spaced holes 4
  • Bring the beans to pH 4.8 or lower before inoculating 1
  • If the beans smell off or feel slimy, discard them

Wet, sticky or slimy beans

Discard the batch. Do not try to rescue it.

Likely causes

  • Beans not dried after cooking: free water encourages spoilage 4
  • Bacterial growth; a sticky, shiny coating was a sign of Bacillus cereus in tests 1

What to do

  • Discard the batch
  • Next time dry the beans well and acidify them to pH 4.8 or lower 41

Ammonia smell, browning, beans showing again

Discard the batch. Do not try to rescue it.

Likely causes

  • Over-ripe tempeh: incubated too long or too warm, and the pH has risen above 7.5 34

What to do

  • Discard: a fresh tempeh has no ammonia smell 2
  • Next time stop at the end of the time range and chill straight away 4

Grey or black patches

Likely causes

  • Spores of the tempeh mould, usually near air holes where it gets more air 41

What to do

  • Small patches are acceptable in otherwise white, fresh-smelling tempeh 4
  • Use smaller holes or stop a little earlier next time 4

The batch got hot

Likely causes

  • Active mould growth releases heat; packs can reach 40–50 °C, which is too hot for the mould 43

What to do

  • Use thinner layers, space the packs apart and let air move 4
  • Lower the incubator setting once white growth is visible 3

Pink, yellow or green mould, or a sour smell

Discard the batch. Do not try to rescue it.

Likely causes

  • Contamination; good tempeh is a white cake 2

What to do

  • Discard the whole batch
  • Check the starter source and the cleanliness of the equipment 5

Change one thing at a time

When a batch disappoints, compare it with the method, change one variable, and note the result in a Batch Card. Two changes at once hide which one helped.

Sources

  1. Wickware (2015), Critical parameters for the production of safe soybean tempeh, Cornell University thesisLactic acid to a whole-bean pH of 4.8 or lower controlled Bacillus cereus; acetic acid at the tested pH did not; unacidified beans fermented poorly; backslopping soak water discouraged; sticky shiny beans signalled B. cereus. Accessed 2026-10-09.
  2. Codex Alimentarius: Regional standard for tempe (CXS 313R-2013)Tempe is a compact white cake of dehulled boiled soybeans fermented with Rhizopus; compact when cut, white mycelium, fresh odour without ammonia. Accessed 2026-10-09.
  3. Okada (1989), Role of microorganisms in tempeh manufacture, JARQAbout 1–2 days near 27 °C; temperature rises once mould growth is visible; over-ripe tempeh shows spores and ammonia as pH rises above 7.5. Accessed 2026-10-09.
  4. Nout and Kiers (2005), Tempe fermentation, innovation and functionality, Journal of Applied MicrobiologyProcess: dehull, soak 6–24 h, cook 20–30 min, dry, cool, inoculate, pack 3–5 cm in perforated bags, 24–36 h at 30 °C or 48–72 h at 25 °C; self-heating to 40–50 °C; spores with more air; tempe is cooked before eating. Accessed 2026-10-09.
  5. Griese et al. (2013), Gastroenteritis outbreak associated with unpasteurized tempeh, Emerging Infectious DiseasesA 2012 outbreak linked to unpasteurised tempeh; the outbreak strain was found in Rhizopus starter culture. Accessed 2026-10-09.

Numbers on this page come from these sources. Where sources give a range, we quote the range rather than a single figure.

All troubleshooting guidesKeep a note about this problem