3. Current and past technologies for the industrial recovery of tannins

3.1 Leather manufacturing

Leather manufacture is still the most widespread use of plant-based tannins. Leather was traditionally made in floor pits in which alternating layers of animal hides and wood shavings (oak, for example) containing tannins were placed and left to soak for considerable periods of time. The hides were stored in a number of consecutive pits, usually 28, so as to be slowly enriched and hardened by the tannin in solution. The tannins exfiltrated from the wood shavings impregnated the hides more and more. Such a manufacturing system produced high-quality leather, but it often took a whole year for the leather to be ready. This technique was used for many centuries. The first change came when the tannin extraction industry, which had boomed in the 1850s to supply...