Black bean tempeh with black spores and sour taste

[salto]

I had a strange fail with my usual succesful black beans tempeh. 300 Grams black beans, soaked 24 hours and cooked in pressure cooker. Fermented with 1 teaspoon Indopal and 2 teaspoons Lactic Acid in incubator at 30°. After one day a tiny bit of colonisation visible on the outside. After two days the outside colonisation had grown just a little, inside temperature 39°. Lowered temperature of incubator from 30° to 27°. Day 3 I gave up, the colonisation on the outside turned out to be black with yellowish spots and the taste was very sour. I have no idea what went wrong, any clues most welcome.
Thank you for your kind interest.
https://photos.app.goo.gl/HTTK4pBpf92SyDwD7

[ArthurDent004]

First question would be what was different this time from your last successful batch.

One teaspoon of starter seems like a lot for 300 grams of black beans. I would use that much starter for 900 grams of beans. I've never used lactic acid either, I either soak long enough to lower the pH or use vinegar but two teaspoons seems like a lot for 300 grams of black beans. I use 1 tablespoon of vinegar for 900 grams of beans.

For the tempeh I make I turn off my incubator after 18 hours because my tempeh is generating more heat than the incubator is providing. My tempeh is ready between 26 to 32 hours total incubation time.