speaking of intentionally rotten, delicious food I have some nattō from my trip to Düs yesterday, think I'm gonna boil some rice and have nattō with the rice 

*that's* a thing I should DIY, it's too expensive to buy in Germany in the quantities I'd consume in Japan and plus I can only get it going in person to a larger-size asiamarkt (because many brands have fish sauce in it, and the German labels is spotty, so I need someone who can read kanji to make double sure there's no fish in the nattō, and I'm the only person I know who can read kanji and I feel comfortable asking to do groceries for me.)

nattō isn't fiddly to make, is it? I think it's basically a matter of getting the starter culture? but how expensive is the starter culture in Germany, I don't think it's a thing like yoghurt or kefir that you can keep reproducing…?

hmm, worse than I thought: it's fiddly with contamination and wants warm temperatures to incubate, it's more work-intensive than kimchi.

but better than I thought: you can in fact propagate a culture by mixing in the last spoonful of your previous batch with fresh soybeans to continue

looks like commercial products are alive so you can even make them from industrial nattō as a starter, like yoghurt
@elilla I once mixed cream cheese with Gorgonzola. Next day the blue mold had started eating through the cream cheese. It was so delicious.
@elilla you might be able to use store bought natto as a starter.
I did that; also imported starter years back, but then forgot about it (because I just kept using my own natto, several generations downwind from that original store bought starter natto ^^).
Kinda easy to make, imho; hardest part is keeping the temperature "just right". Hacky approaches can an oven with the door kept slightly ajar and either very, veeeery low settings and a good thermometer, or just the oven light on.