Question Summary:
the rennet from animals slaughtered with tasmiyyah will be permissible, but what about the rennet from at once halal, but murdaar animals and from porcine sources? Why can’t a consensus be reached upon the latter issue?

Question Detail:

Assalamualaikum,

In the US, there is a lot of debate about the permissibility of animal rennet produced cheeses.  A lot of dietary products that Muslims come across are only doubtful due to the cheese issue.  Milk, having liquid consistency, is coagulated using an enzyme called rennet.  Rennet can be extracted from microbial as well as animal sources.  There is open consensus about the permissibility of the microbial rennet.  The rennet extracted from the intestinal tract of animals remains open to debate.  Obviously, the rennet from animals slaughtered with tasmiyyah will be permissible, but what about the rennet from at once halal, but murdaar animals and from porcine sources?  Why can't a consensus be reached upon the latter issue?  Please read the content on this website and reply with your response on the issue:
http://muslimmatters.org/2007/07/09/of-mice-and-men-the-cheese-factor .  This document has been prepared by a traditional student of 'ilm.  Jazakallah!

Wassalaamualaikum.

Answer :

In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatoh

Allah Ta’ala has created mankind and chose the religion of Islam for them.  Islam, unlike the other religions, is a complete way of life.  It does not constitute only of Salah, Sawm, Zakah, and Hajj, but involves every aspect of one’s life.  To such an extent, that even the food one consume must also be according to Shariah.  One cannot eat all which his heart desires, instead he is ordered to eat only that which is pure and lawful.
Allah Ta’ala says,
يَا أَيُّهَا الَّذِينَ آَمَنُوا لَا تُحَرِّمُوا طَيِّبَاتِ مَا أَحَلَّ اللَّهُ لَكُمْ وَلَا تَعْتَدُوا إِنَّ اللَّهَ لَا يُحِبُّ الْمُعْتَدِينَ . وَكُلُوا مِمَّا رَزَقَكُمُ اللَّهُ حَلَالًا طَيِّبًا وَاتَّقُوا اللَّهَ الَّذِي أَنْتُمْ بِهِ مُؤْمِنُونَ (المائدة)
O you who believe, do not hold as unlawful the good things Allah has made lawful for you, and do not transgress.  Verily Allah does not like the transgressors.  And eat from what Allah has provided you as good and lawful, and fear Allah in whom you believe
(al-Maa’idah 87-88)
 
It is in the spirit of pursing halal, the issue of cheese is being researched and it particular at rennet as it is the key ingredient of cheese.
 
Rennet
Rennet is a natural complex of enzymes produced in the lining membrane of the fourth stomach of mammals.  The active enzyme in rennet is rennin (chymosin).  There are other important enzymes as well, e.g. pepsin or lipase.
 
The role of chymosin is to curdle the milk in the stomach, which is essential for young animals so that milk does not just follow through without it gaining the necessary proteins.  Chymosin secretion is at maximum during the first few days after the birth and decreases thereafter.  For this reason, the younger the animal the stronger the enzymes will be.
 
After people discovered the effect rennet had upon milk, they began drying and cleaning the stomachs of young calves and extracting the rennet from it.  The rennet would be added in milk to turn it into curd and whey.
 
Rennet can also be derived from non-animal sources. In the past people also used rennet from fig leaves, melon, wild thistle and safflower for cheese making.  The most widely used non-animal rennet is by fermenting a fungus called Mucor miehei.
In today’s time, genetically engineered rennet has also become common in cheese making.
 
The method of making cheese
First the milk is heated to destroy any possible harmful bacteria and then cooled.  The milk is then acidified by a starter culture of lactic acid bacteria added with rennet to curdle the milk.  Some cheeses are curdled only by acidity but most use rennet.  After curdling, the curds are removed, cut and drained.  Thereafter it is matured and processed into the various different cheeses.
 
Shar’ee Ruling for animal rennet
The practice of making cheese is very ancient and was done well before the time of Rasulullah (Sallalahu Alaihi Wasallam).  Cheese was made for the reason that it was a means of preserving food which could last for a long period of time. Rasulullah (Sallalahu Alaihi Wasallam) himself was presented cheese made by the Persians (the Magians) which he ate.
 
The Shar’ee ruling of rennet is that if it is derived from an unlawful animal, then the rennet will be unlawful.  Thus rennet extracted from pigs and other non-lawful animals will not be lawful to consume.
 
If the animal is lawful and slaughtered in accordance to Shariah, then the rennet will be lawful to consume.
 
As for rennet extracted from lawful animals that are not slaughtered in accordance to Shariah, there is a difference of opinion between Imam Abu Hanifa and his two students, Imam Abu Yusuf and Imam Muhammad.  All three Jurists agree that rennet itself is pure.  However, Imam Abu Yusuf and Imam Muhammad state the rennet is in contact with the liquids of the stomach which become impure upon death of the animal if not slaughter in accordance to Shariah.  Therefore, if the rennet is in solid from, it is possible to purify is by washing it.  If it is liquid form, it is not possible to purify it and will be impure.  Imam Abu Hanifa states that the liquids of the stomach do not become impure upon the death of the animal, therefore the rennet will be pure regardless if its slaughter in accordance to Shariah or not. 
 
The ruling in Hanafi Fiqh is giving upon the view of Imam Abu Hanifa, therefore if the rennet is extracted from lawful animals it is lawful to consume, regardless if it is slaughtered in accordance to Shariah or not.
- عن ابن عباس قال أتى النبى صلى الله عليه وسلم بجبنة فى غزاة فقال أين صنعت هذه فقالوا بفارس ونحن نرى أنه يجعل فيها ميتة فقال اطعنوا فيها بالسكين واذكروا اسم الله وكلوا (مسند احمد)
- عن ابن عمر قال أتى النبى صلى الله عليه وسلم بجبنة فى تبوك فدعا بسكين فسمى وقطع (سنن ابى داود)
- قوله : كالشعر الخ والمنقار والمخلب وبيضة ضعيفة القشرة ولبن وإنفخة وهي ما يكون في معدة الجدي ونحوه الرضيع من أجزاء اللبن قبل أن يأكل قال في الفتح لا خلاف بن أصحابنا في ذلك وإنما الخلاف من حيث تنجسهما فقالا : نعم لمجاورتهما الغشاء النجس فإن كانت الأنفحة جامدة تطهر بالغسل وإلا تعذر تطهيرها كاللبن وقال أبو حنيفة ليستا بمتنجستين لأن الموت لا يحلهما (حاشية الطحطاوى على مراقى الفلاح ص 169 دار الكتب العلمية)
- ( وشعر الميتة ) غير الخنزير على المذهب ( وعظمها وعصبها ) على المشهور ( وحافرها وقرنها ) الخالية عن الدسومة وكذا كل ما لا تحله الحياة حتى الإنفحة واللبن على الراجح...قال ابن عابدين: ( قوله حتى الإنفحة ) بكسر الهمزة وقد تشدد الحاء وقد تكسر الفاء . والمنفحة والبنفحة : شيء واحد يستخرج من بطن الجدي الراضع أصفر فيعصر في صوفة فيغلظ كالجبن ، فإذا أكل الجدي فهو كرش ، وتفسير الجوهري الإنفحة بالكرش سهو قاموس بالحرف فافهم . ( قوله على الراجح ) أي الذي هو قول الإمام ، ولم أر من صرح بترجيحه ، ولعله أخذه من تقديم صاحب الملتقى له وتأخيره قولهما كما هو عادته فيما يرجحه (الدر المختار مع رد المحتار 1:206)
- وإنفحة الميتة ولبنها في ضرعها وقشر البيضة الخارجة والسخلة الساقطة من أمها وهي مبتلة طاهرة عند أبي حنيفة رحمه الله . كذا في محيط السرخسي (الفتاوى الهندية)
 
 
Sources:
http://en.wikipedia.org/wiki/Rennet
http://en.wikipedia.org/wiki/Cheese
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/stomach/rennin.html
http://biology.clc.uc.edu/fankhauser/Cheese/Rennet/Rennet.html
http://www.vegsoc.org/info/cheese.html
Is cheese containing Animal Rennet Halal? by Mufti Zubair Butt (PDF)