Koji (*Aspergillus oryzae*) is the mold used to make sake, miso, soy sauce, and mirin. It produces amylases (break down starches) and proteases (break down proteins into amino acids, including glutamate).

Dry-aging beef is partly enzymatic: the meat's own proteases break down connective tissue and muscle proteins over days or weeks. Koji accelerates this to hours. A koji-treated steak develops aged-beef complexity in 48 hours.

The principle generalizes: enzymes are time machines for flavor development. Understanding what enzymes do tells you what time does.

Related: [[fermentation-as-preservation]], [[umami-fifth-taste]]