Enzyme biology · protease ↔ amylase
Enzyme Balance
Same spore, different koji. Amylase builds sweetness, protease builds umami — and which one the mould favours is something you set, not something you get. Strain, substrate, temperature, moisture, and bed depth each pull the dial one way or the other; see which lever is actually doing the work.
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Koji is not a flavour in itself — it is a delivery system for two families of enzymes, and every ingredient a koji ferment ever makes comes out of those two. Amylase cuts starch into sugar, so the koji tastes sweet and a ferment built on it turns sweet: amazake, sake, white miso. Protease cuts protein into free amino acids, which is what savoury depth actually is: shoyu, garum, dark miso. The mould makes both, and the ratio is set by how you run the batch.
- Substrate —
- the cooked grain or bean the mould grows on. Starch-rich material gives amylase more to work with; protein-rich material favours protease.
- The bed —
- the layer of inoculated grain spread on a tray. Thin breathes and dries; thick holds its own heat and moisture, which is why depth is a lever and not a detail.
- Yield vs. balance —
- the dial says which enzyme you are favouring; the yield number says how much enzyme there is at all. A perfect balance at low yield is still weak koji.
- Sporulation —
- the mould going to seed — a yellow-green dusting on the bed. Flavour turns bitter past this point, so the harvest deadline is real.
Amylase-dominant. Starch to sugar, the amazake and sake direction. Very little protease, so expect sweetness without much umami.