Fermented soy sauce is a complex mixture produced by microbial fermentation of soybeans and wheat, containing amino acids (e.g., glutamic acid), peptides, organic acids (lactic, acetic), sugars, alcohols, aldehydes, furanones, and phenolic compounds. These contribute to umami flavor, color via Maillard reactions, and aroma. The primary compounds arise from Aspergillus oryzae or sojae koji fermentation followed by lactic acid bacteria and yeast. It is highly soluble in water due to polar components but shows variable solubility in alcohol and low in fats. Used as a seasoning, it provides savory taste without being a single chemical entity. Properties vary by brand, fermentation time, and raw materials.