Rennet is one of the enzymes used to make cheese. Rennet comes from the stomach of young calves. After the calf is slaughtered/killed, the stomach is removed, filled with milk and hanged to dry. After it dries, it is ground up to make crude extract of rennet, which is then purified or sold as is. If the calf is slaughtered according to Islamic requirements, the rennet is halal. Otherwise, it is not.
The active ingredient in rennet is chymosin. Chymosin can also be produced by other means, including biotechnology. Chymosin produced using biotechnology is halal.
If an ingredient label states the product in question contains rennet, then the rennet came from an animal source. As such, items containing rennet must be considered questionable for the halal consumer until the source is known. If the source calf was not processed according to Islamic law, the product is not acceptable for halal consumption. In general, most rennet produced in the US comes from calves that have not been processed in accordance with Islamic requirements, so the rennet produced is not acceptable.
If the product containing the rennet is halal-certified, the source of the rennet should be halal. IFANCA has received a number of inquiries from consumers regarding rennet – some believing that rennet is extracted from live calves. This is not the case. Rennet is not extracted from live calves. It is extracted from slaughtered (dead) calves.
And ALLAH, Subhanahu wa ta’ala, knows best.