Amino acid
Japanese: アミノ酸
The building blocks of protein. Twenty types exist, among which glutamic acid and aspartic acid are the source of umami flavor.
Amino acids are the smallest units that make up proteins. Twenty types exist in nature, combining in countless ways to form the vast diversity of proteins.
In the context of fermentation, what matters most is that amino acids are the essence of umami. During miso aging, proteases from koji mold break down soybean protein, releasing free amino acids such as glutamic acid and aspartic acid. These stimulate umami receptors on the tongue, creating that deep, satisfying flavor.
The longer miso ages, the more amino acids accumulate, and the richer the umami becomes. Amino acids quietly prove fermentation's fundamental truth: time creates flavor.