2,301. Non-Jewish Cheese

Maachalos Assuros 3:13

Pursuant to the previous halacha, it would make sense for any milk in the possession of a non-Jew to be prohibited out of concern that he may have mixed milk from a non-kosher species into it, while the cheese of the non-Jews should be permitted because milk from a non-kosher animal won’t make cheese. Despite the logic underlying this, the Sages of the Mishna prohibited non-Jewish cheese out of concern that non-Jews might congeal it using skin from the stomach of an animal they slaughtered, which is prohibited as neveila. If you suggest that the stomach skin is insignificant compared to volume of milk that it congeals, it’s not nullified because it’s the necessary catalyst in curdling the cheese. Since the catalyst is prohibited, the whole thing is prohibited, as will be discussed IY”H in future chapters.

Maachalos Assuros 3:14

If cheese was left to coagulate with herbs or with fruit juice and it’s obvious that this is the case, some Geonim prohibit it because the Sages already prohibited all non-Jewish cheese regardless of whether they were coagulated using a prohibited or permitted substance. This decree is because non-Jews use prohibited substances.