I'm making a first time natto in natto/black garlic pot. So I go by the recipe.

First soak beans for 24 h then steam to be softer. Put natto starter inside a small amount of water and mix it with soya. Put soya beans in machine, add mixed starter and ferment for 24 h in 39 oC.

I tried to keep everything sterilized.

Proportions were:

  • 500 g soya beans
  • 3 g starter mixed with 2 0ml water

So then I just checked soya inside device after 20h and there is kind of white texture on it. Not sure if it's natural, or it's mold. Is it normal to happen, or I did something wrong?


  • 1
    I’ve not made natto but it just looks like it’s fermenting to me, which is what you’re trying to accomplish.
    – Preston
    Commented Mar 19, 2022 at 4:02
  • In terms of food safety, white mould is usually not an issue. There's a quote in "Wild Fermentation" about it (excellent book BTW). But I'm not near my library at the moment. Given the beans were sanitised by cooking, and you added a culture, and tried to keep everything clean, and it's only 20 hours later, I'd say that's the Natto culture at work.
    – Kingsley
    Commented May 26, 2022 at 5:38

1 Answer 1


This looks like fungus beginning to develop. Compare with https://youtu.be/INlM39t2aDg?t=125.

Did you try mixing it up, to see how much slime is produced? Does your Natto smell right?

If you let Natto ferment too long, it starts to change in texture, and taste/smell like ammonia. Did you perhaps ferment for too long?

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