Free amino acids
Japanese: 遊離アミノ酸
Amino acids that exist independently, separated from proteins. It is free amino acids in this state that the tongue can taste.
Free amino acids are amino acids separated from protein chains, existing independently. While still part of protein they have no taste, but once freed, they interact with taste receptors on the tongue, generating umami and sweetness.
Free amino acid content in miso correlates closely with aging time. Near zero at preparation, it surges at three months and continues rising beyond one year—the result of proteases continuously breaking down protein over time.
Free amino acid levels are measured as 'amino nitrogen,' an important metric for miso quality evaluation. Higher values mean more advanced protein breakdown—meaning richer umami.