Butyric acid
Japanese: 酪酸（ブタン酸）
A short-chain fatty acid produced by gut fermentation that serves as energy for intestinal lining, also the distinctive aroma component of nukazuke.
Butyric acid is a four-carbon short-chain fatty acid. Named after 'butyrum' (butter), it contributes to the distinctive fermented aroma in dairy products and nukazuke.
Recently, butyric acid has gained significant attention in the context of gut fermentation. When gut bacteria ferment dietary fiber, butyric acid is produced, serving as the primary energy source for colon epithelial cells. Effects on maintaining gut barrier function and suppressing inflammation have been reported.
In fermented foods, butyric acid sits on the boundary between 'pleasant aroma' and 'unpleasant odor.' It is one component of nukazuke's complex flavor, yet in excess becomes an off-flavor. Quantity and context determine the value of an aroma.