What are the dangers of Tempeh cultures (Rhizopus Oligosporus and Rhizopus Oryzae) ?

After handling raw Tempeh you should wash your hands and all surfaces, cutting boards, knives and utensils with soap and hot water. Tempeh manufacturers that sell raw Tempeh must inform their clients about above safety measures, for example by mentioning it on the label. -https://www.tempeh.info/faq/faq.php

  • Sounds like the raw product could easily become host to harmful bacteria. Treat it like raw chicken. Nov 21, 2017 at 11:50

2 Answers 2


Rhizopus Oligosporus is believed to be "harmless" on the basis of the fact that there has never been a recorded incident of Rhizopus Oligosporus' ability to produce a toxin when fermenting Tempeh, but then again, Rhizopus Oligosporus is believed to be a form of Rhizopus microsporus. The latter one is a documented pathogen that does produce toxins, even several different ones.

The problem, in my view, is twofold:

  1. Rhizopus Oligosporus shares large parts of its genome with Rhizopus microsporus, a pathogen (quoting Wikipedia):

R. microsporus produces several potentially toxic metabolites, rhizoxin and rhizonins A and B, but it appears the domestication and mutation of the R. oligosporus genome has led to the loss of genetic material responsible for toxin production.

  1. The genome of Rhizopus Oligosporus has not been sequenced fully, which means that we really don't know how much of the ability to produce poisons it has inherited from it's toxic relative. The ability of R. Oligosporus to produce toxic metabolites could be re-activated in response to environmental stressors such as exposure to radioactivity or EMFs. Until its genome has been fully sequenced, it's definitely a gamble, which could explain why Tempeh, traditionally, is cooked and/or baked after fermentation, NOT eaten raw!

As for Rhizopus Oryzae, it's an even nastier fungus of the same family that has the ability to infect and damage human endothelial tissue (your blood vessels): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC547117/

I could imagine it being a contributing factor, if not a cause, of things such as deep-vein thrombosis.

I would stay away from Tempeh in any form, baked or not. If you want to ferment beans, I'd go with Natto (Bacillus Subtilis natto) or Koji kin (Aspergillus oryzae; it can ferment rice, beans and other foods).

I'd stay away from the Rhizopus family in all forms. The benefits aren't significant and it's hardly worth the risks.


Some people develop an allergy to the fungi in the tempeh and the fungus was suspected of being causative of Zygomycosis. IIRC that may now have been disproved and Rhizopus is generally considered safe in food stuffs.

  • 1
    can you please link to your sources? or where you found this information.
    – jsolarski
    Nov 21, 2017 at 21:05

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