Making Douchi from scratch
Sandor Katz's Art of Fermentation has a recipe for douchi (link).


  Soybeans (yellow or black) are soaked, cooked until soft, cooled, inoculated with Aspergillus spores or mixed mold cultures, and incubated around 80–90°F/27–32°C for about 72 hours, until the mold on the beans turns green, indicating sporulation. In contrast to the hamanatto method described above, in the douchi method the beansare not dried at this stage but rather washed, to remove the spores, which would impart bitter flavor. For the second-stage fermentation, the beans are fermented in brine, sometimes with sugar and/or hot chili paste, for four to six months, then dried.