How is glycerin halal if it is found inside an animal and has not undergone a process of transformation (istihalah)?

Transmutation means the change of the essence of an impure or prohibited substance, and the transformation of its very nature into a different substance in name and characteristics. This chemical change purifies it and renders it permissible. Although the original substance may have been one, after transmutation, each of its components acquires its own name and ruling. Accordingly, glycerin extracted from animal fats is considered pure and permissible for use after its decomposition and change in characteristics.