Koji, miso & soy.

Koji is steamed rice, barley or soybeans grown with the mould Aspergillus oryzae. Its enzymes break starch into sugar and protein into amino acids, which is what gives miso, soy sauce, sake and amazake their sweetness and savoury depth.

Yes, when it is made with enough salt (typically 10–13% for long-aged miso), packed without air pockets, and kept covered. The salt and acidity keep spoilage organisms out; a little white yeast on the surface is normal and is scraped off.

Koji, tempeh and natto need steady warmth (about 30–40°C depending on the culture) for a day or two, which an oven with the light on, a proofing box or a dehydrator can provide. Miso and soy sauce just need a crock and time.