Rennet, it does a cheese good.
Rennet is the ingredient that allows milk to change from liquid into cheese.
There is a great misunderstanding regarding the concept of Rennet in the making of Kosher Cheese. Many believe that if cheese is made with animal rennet, there would be a violation of Basar vChalav (the prohibition of mixing/eating meat and diary). I am glad to say that would not be the case. How the animal rennet is obtained is where there is much concern though. Our sages made a ban on cheese that was made by non-Jews because of the fear that perhaps a piece of stomach was put in the milk and that is what made the cheese.
Everybody probably knows the story of how cheese came to being. Once upon a time, there was a nomad that put his milk in his canteen pouch (made from an animal stomach) and went on his journey. When he arrived to his destination he took the top off of the pouch held it to his mouth for a drink and out came a coagulated kind of cheesy thing.d How did that happen? Well the heat warmed up the stomach bag as well as the milk that was in the pouch. The rennen that was in the stomach lining acted on the milk and started the process of making curds.
So we see that it is true that by putting milk in side a dried animal stomach we can get curdled milk. Is it kosher, no. But what is rennet really? Can it truly be Kosher?
Rennet is from an enzyme found in the 4th stomach of a kosher animal (animals that chew their cud have 4 stomachs). It is known and documented that milk that has been obtained from non-kosher mammals can not be made into cheese. The milk will simply not coagulate under normal circumstances. So everybody that has heard of the Camel cheese craze, you need to understand that the Camel milk was combined with kosher milk, and the kosher milk is making the cheese not the Camel milk. This is even brought down in Rambam Halacha #12 which states in his sefer Mishnah Torah section Ma’achalot Assurot – Chapter 3:12
The milk of a non-kosher animal will not congeal and solidify as the milk of a kosher animal does. If the milk of a non-kosher animal is mixed together with the milk of a kosher animal, when the mixture is [set aside for cheese to be made], the kosher milk will solidify and the non-kosher milk will be expelled together with the whey of the cheese.
In order for Rennet to be kosher though the animal needs to be schechted (slaughtered according to Jewish law) and deveined according to halacha (Jewish law). Once this is done the milk stuff that is the stomach and full of rennin is removed and that is what is used to make milk (from a kosher animal) into cheese. As this milk stuff has been already digested it does not have a status of food.
Since the process involved is time consuming and very expensive it is very rare that you will find Kosher rennet from an animal.
I read that there is someone in Israel that stated he is making rennet from the stomach of either cows or goats that had been killed on the road. It would be true that he is making rennet, but the cheese that he makes from it is not fit for Jewish kosher consumption as the animal is a Nevaila (died from disease or injury).
All vegetable based coagulants (such as fig juice as used in days long gone) are Kosher, but only if they are added to milk by a Torah observant Jew will the cheese be kosher. This is because of a halachic restriction from the time of the mishna
All Microbial enzyme is generally kosher and will follow the same rules as vegetable based coagulants (though it’s possible it may be grown on a non-kosher medium, and therefore should be checked or certified before purchase or use).
Feel free to enjoy some kosher cheese with your Shavuos holiday meals!