Castaneum

Castaneum is a substance derived from the bark of the chestnut tree, specifically the American chestnut (Castanea dentata) and the European chestnut (Castanea sativa). This extract has historically been used for its tanning properties, similar to other vegetable tannins found in plants like oak bark or quebracho. The primary compounds responsible for its tanning capabilities are tannins, which are complex polyphenolic molecules. These compounds bind to collagen fibers in animal hides, transforming them into leather through a process called tanning.

The use of castaneum as a tanning agent has largely been superseded by more efficient and consistent synthetic tanning agents or other well-established vegetable tannins. However, it can still be found in niche applications within the leather industry, particularly for producing specialty leathers where specific color, feel, or historical authenticity is desired. The extract typically imparts a reddish-brown hue to the leather. Beyond leather tanning, research has explored other potential applications of chestnut extracts, including as a natural dye and for their antioxidant properties, though these are not widespread commercial uses. The harvesting of chestnut bark for commercial purposes needs to be managed sustainably to avoid detrimental effects on the trees.