Oak transforms wine through multiple mechanisms. It adds flavours like vanilla, spice, toast, and caramel whilst contributing tannins that provide structure and texture. Oak allows controlled micro-oxygenation, which softens harsh edges and develops complexity. The wood's natural compounds - vanillin, lactones, and phenolics - integrate with wine over months or years, creating rich, layered flavours. Oak also affects mouthfeel, adding creaminess and weight that makes wines feel more luxurious and substantial.