Why is the use of rennet - stomach lining calves in preparing cheese not seen as a mixture meat and dairy according to kosher standards?

You are correct to point out that rennet, traditionally derived from the stomach lining of calves, is an animal product. However, the use of rennet in cheesemaking is not considered a mixture of meat and dairy under kosher standards because of a few key factors:

* The nature of rennet: While rennet is derived from an animal, it is not considered "meat" itself. It is an enzyme, and the process of extracting and purifying rennet separates it from the meaty components of the calf's stomach.

* The purpose of rennet: Rennet's role in cheesemaking is to coagulate milk, which is a dairy product. The rennet itself doesn't contribute any significant meaty flavor or texture to the final cheese.

* The Rabbinic rulings: Rabbinic authorities have ruled that rennet is permissible for use in cheesemaking, even though it is derived from an animal. They have considered the separation of rennet from the animal and its role in the dairy process.

Therefore, while rennet comes from an animal, its use in cheesemaking is generally accepted as kosher.

However, it's important to note that some kosher certifications specifically require the use of vegetable rennet, which is derived from plant sources. This is because there are concerns about the humane treatment of calves in the traditional rennet extraction process.

In conclusion, the use of rennet in cheesemaking is not seen as a mixture of meat and dairy under kosher standards because of the nature of rennet, its purpose in the dairy process, and Rabbinic rulings. However, some stricter interpretations may require the use of vegetable rennet.