What did Fermentation Starter Culture (Qu / Koji) look like?

Grains are steamed, then inoculated with naturally occurring molds and yeasts from the environment → incubated under controlled temperature and humidity → grain surfaces become covered with mycelium → dried → the result is qu (fermentation starter).

How did Fermentation Starter Culture (Qu / Koji) work?

Grains steamed to sterilize → provide starch substrate → under suitable temperature and humidity → Aspergillus molds naturally inoculate → secrete amylase → starch → sugars → Saccharomyces yeast ferments → ethanol → dried and stored.

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Fermentation Starter Culture (Qu / Koji)

The world's earliest microbial engineering application: cultivating Aspergillus molds and yeasts on cooked grains to create a fermentation starter (qu/曲) that simultaneously saccharifies starch and ferments sugar — a one-step process Western brewing only achieved millennia later.

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Scientific Principle

Solid-state fermentation (SSF): Aspergillus oryzae secretes amylase → starch → glucose; Saccharomyces cerevisiae converts glucose → ethanol + CO₂. The two processes (saccharification and fermentation) occur simultaneously in the same vessel — called 'parallel fermentation' or 'complex fermentation.' Zhou et al. (2023, PMID:37689429) confirmed the Aspergillus-bacteria community interaction in traditional Jiangqu via 16S rRNA sequencing. Song et al. (2025, Foods) published a comprehensive review of qu microbial diversity. SSF is now a core bioprocess engineering method for enzymes, organic acids, and biofuels.