Is it permissible to eat cheese made in the United States given it contains rennet from animal sources?
Rennet that is extracted from a muhallal or lawful to eat animal is pure even if the animal was not slaughtered according to Islamic laws. However, some companies use the internal lining of the animal’s stomach/intestines, which is impure if taken from animals that are not slaughtered according to Islamic laws. Thus, even if the rennet is pure, it becomes mutanajjis because of wet contact with the lining, and so it is unlawful to consume. In the case you do not know if the cheese is made with impure ingredients it is lawful to eat it and you do not have to investigate.