Vegetable tannins are natural products contained in various parts of trees (e.g. bark, wood, pods etc.). The chemical constituents of vegetable tannins are composed of polymeric polyphenolic molecules. The molecules of vegetable tannins cover a wide range of molecular mass ranging from 500 to 3000 units.
In South Africa, Wattle extract is obtained from the bark of Black Wattle (Acacia mearnsii) trees grown in plantations. It takes 7 to 10 years for the tree to grow large enough to be ready for cutting down and stripping of the bark, which is then chipped and extracted under controlled industrial conditions to extract the optimum amount of tannin with the lightest of colours. Wattle bark contains about 30% tannin. The wood has other industrial uses.
Wattle bark is best extracted immediately after stripping to give extract of light colour; the older the bark, the darker is the colour. Sometimes the bark has to be dried out before the extraction process, but this gives a dark coloured product. There is a definite season for stripping the bark depending on the weather and rainy season in the country where it is grown. At the NTE factories, chopped bark is extracted, using a counter current principle, in autoclaves under pressure at temperatures above 100 degrees Celsius. The liquid extract so obtained is then concentrated by evaporation and either poured into Hessian bags, in which it slowly solidifies and becomes a solid, or the hot viscous concentrated liquid is either spray dried as is to a natural powder or certain chemical are combined and then spray dried as powder. The powder is placed into bags, which are stitched closed and carefully stacked.