Natto

For this, I had a:

• Cotton towel
• Instant pot pro plus
• bowl
• steamer

This is specialized wrt portioning s.t. the result fits in my instant pot/bowl.

• Soak 500g soybeans in water overnight. Make sure there's ample water since the soybeans significantly increase in size
• Steam the beans for 1 hour (to preserve texture). Really put in as much water as possible without the water touching the steamer.
• Let beans cool to 105-109F (takes about an hour)
• Move natto to bowl
• Insert some existing natto that's been thawed in the fridge if frozen (I error on the cautious side and add a bunch of starter)
• Add 5tbps of the steamer liquid to the bowl for moistness
• Throughly mix to distribute natto
• Put cotton towel on top of bowl
• Put new, boiled water (I did RO-ed) water into pressure cooker
• Run "Yogurt mode" for 16.5 hours at 103F
• The result smells faintly of amonia, and is very stringy. It also really tastes and smells like natto.
• Refrigerate result for a few days, then freeze (optional)

Ideally I would both clean and sanitize the equipment prior to the natto. Natto is basic not acidic, so it's a bit unusual in that sense. This makes sanitation more important (it seems that acidity kills bacteria).

However, I did neither clean nor sanitize and I got "lucky". Natto out competed any of the other growing organisms. I attribute this to using several tbps of natto (e.g. a LOT of starter).