The World Federation One Stop Fiqh

Ruling 189

If the essence of an impure object changes in such a way that it transforms into a pure object, it becomes pure; for example, if impure wood burns and transforms into ash, or a dog falls into a salt marsh and transforms into salt [the ash and the salt are pure]. However, if the essence of the object does not change – for example, if impure wheat is turned into flour or made into bread – it does not become pure.