Mars Bars - Kosher in London, Not Kosher in Manchester
London BD and Manchester BD disagree about trace amounts
Rabbi J Conway London Beis Din
trace amounts of non-Kosher does not present a problem
to isolate us from the society around usRabbi H Royde Manchester BD
why should we resort to looking for leniencies?
Our Sages decreed many regulations in order to isolate us from the society around us
Rennet from a non-Kosher animal may be used to make Kosher cheese
Our Sages forbade the cheese made by our non-Jewish neighbours [which is Kosher] in order to preserve our national identity
our Sages did not prohibit
animal rennet, it is not a food.
They forbade the flesh
of the stomach
which contained the rennet
Poskim permit animal rennet
for making cheese
since it is
not a food
see this OU article
There is no Kashrus issue to make cheese with animal enzymes since
they are tasteless i.e. not a food
the amounts used are minuscule. The Davar HaMaAmid principle only applies to non-kosher substances, and the animal enzymes are actually kosher.