Oak galls have a much high tannic acid content than any other part of the tree, 4 or 5 times higher if memory serves. It is also much easier to get to the tanni

Oak galls have a much high tannic acid content than any other part of the tree, 4 or 5 times higher if memory serves. It is also much easier to get to the tannins than in the wood which has better uses like lumber and fuel.