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.