2,363. Hot on Cold, Cold on Cold

Maachalos Assuros 9:16

It’s prohibited to put the skin of a kosher animal’s stomach in milk in order to curdle it into cheese. If one did so, a non-Jew should taste the cheese. If it has the taste of meat, it’s prohibited and if not, it’s permitted. Since the catalyst is something permitted, coming from a kosher animal’s stomach, the question is if it violates meat-and-milk by imparting flavor. If one used skin from the stomach of a neveila, a treifa or an animal from a non-kosher species, then the catalyst is itself prohibited, rendering the cheese prohibited. This isn’t because of meat-and-milk but because of neveila. Because of this, the Sages prohibited cheese made by non-Jews, as has already been discussed (halacha 3:13).

Maachalos Assuros 9:17

Meat is permitted and milk is permitted but the two of them mixed together through cooking renders them prohibited. This is the case when they were cooked together, or one of them fell hot onto the other hot, or one of them fell cold onto the other hot. However, if one of them fell hot onto the other cold, one need only remove the surface of the meat that touched the milk, after which the rest may be eaten. If one fell cold onto the other cold, one must thoroughly wash the meat, after which it may be eaten. Because of this, one may wrap meat and milk in the same cloth so long as they don’t touch. If they do touch, one must wash the meat and the cheese, after which they may be eaten.