Take the 2-minute tour ×  I actually have 2 questions which are
related.    1. Traditionally, making cheese involves using
rennet, a substance derived from animal stomach. If the rennet
is derived from a non-Kosher animal, it is non-Kosher (making
the cheese non-Kosher as well). From my understanding, the
reason for this is the rule "כל היוצא מטמא טמא" - all that is
derived from an unclean (animal) is also unclean. But, even
rennet from a Kosher animal is not considered meat because of
the process involved in extracting it. So, why the difference?
Why does the rennet lose its "meat properties" but not its
"unclean properties"?   2. Suppose we understand the differences
between the meat & unclean properties, what is the difference
between rennet and gelatin made from non-Kosher animal bones? I
read that the opinion of the Shulchan Aruch (99) is that
(completely) dry bones of non-Kosher animals are considered
Kosher, and so gelatin from those bones would also be considered
Kosher. Why does the rule of "כל היוצא