Vegetable Tanning

Vegetable tanning is the jargon term for the use of plant polyphenols, a traditional approach to tanning used for thousands of years. Up to the point when it was overtaken by the introduction of chrome tanning, the sources of plant tannins were many and varied, each having a specific application to the properties and performance required of the product. In the modern industry, vegetable tannins have a place, but the number of species used is limited: mimosa, quebracho, chestnut, sumac, tara and oak extracts are examples. There are two main types of tannins and both are used in the modern industry: hydrolysable, based on a sugar core esterified with gallic acid, and condensed, based on the flavonoid fused aromatic ring system. Each type, therefore, has its own chemistry and its own place in the technology. Pure vegetable tannage is now encountered only in leather for shoe soles. However, they have roles in combinations and in chrome leather. Typically, vegetable tannins were and still are applied in high offers, with little account taken of the differences in structural conformation and no chemical modification other than sulfitation to improve solubility. With the current emphasis on creating tannages without chromium, the use of vegetable tannins and their constituents is having a resurgence.