What You Need to Know
During fermentation Aspergillus oryzae secretes proteases that hydrolyze muscle proteins into glutamyl‑glutamine peptides and other umami‑active peptides, while lipases oxidize fatty acids to aldehydes. Subsequent hot smoking induces Maillard reactions between reducing sugars and free amino acids, generating volatile compounds such as 3‑methyl‑2‑butenol that give katsuobushi its characteristic smoky aroma.
The Science
Primary Reaction
proteolysis and lipid oxidation by mold fermentation followed by Maillard reactions during smoking