©David B. Fankhauser, Ph.D.,
Professor of Biology and Chemistry
University of Cincinnati Clermont College
Batavia OH 45103
13_diced_pieces_P5160004 (-1x-1, -1 bytes)
Four chambers of
the ruminant stomach (labeled)

This page has been accessed Counter times since 18 May 2007. 
The dried abomasum is diced
and extracted in acidified whey.

Here are the results of an experiment at producing home made rennet. Rennin is an enzyme which, in an acid environment, digests the water soluble milk protein casein into insoluble products. When these precipitate out of solution, the milk coagulates. The test is the famous "clean break" of cheese making.

Here, the abomasum of a suckling kid was cleaned, salted and dried. A small piece (0.75 gm) of it was suspended in warm water (30 C), and added to 1 gallon of inoculated milk. While a clean break was not achieved in three hours, by the evening (about 7 hours) the milk had formed a very firm coagulant.

This is my first attempt at using home made rennet.  I am sure that the process and conditions can be improved.  Let me know if you have suggestions.

See the bottom of the page for suggestions from Mr. Wolfgang Pachschwöll,of "Hundsbichler company Austria - producer of natural rennet".
1)  Here is a view of the abdominal contents of a suckling kid.  The lungs and heart are in the lower left, the stomach is in the upper center (liver below) and the intenstines are to the right
9)  Rub the salt into the surface of the abomasum.  Let it dry in a cool dry location.
2)  Here the stomach has been dissected out of the abominal contents.  The duodenum is the to left, the pyloric region and abomasum next (lower left), the reticulum the round structure to the upper  center, and the rumen, the large darker chamber to the right. (Here is a labeled view of the stomach.)
11_dried_abomasum_P5160002 (-1x-1, -1 bytes) 10)  The dried, salted abomasum is laid out, and  30 mL of 30 C water measured out. [Better to suspend in cold acidified whey. See below.]
3)  The stomach chambers have geen opened up to show their interior traits:
abomasum: lower left.
omasum:  small, center (above and R of abomasum)
reticulum: upper left
rumen:  right
Four chambers of the ruminant stomach (labeled)
12_cut_piece_P5160003 (-1x-1, -1 bytes) 11)  Cut off a square of abomasum about 2 cm square.  (About 1 gram)
4)  Here is the interior lining of the rumen, the major fermenting stomach of a ruminant animal.  Note that there are thousands of villi which project in, dramatically increasing the surface area of the rumen.
13_diced_pieces_P5160004 (-1x-1, -1 bytes) 12)  Cut the piece of abomasum into small pieces, stir into the warm water. [Probably not necessary to cut up.]
5)  Here is the reticulum (sold as a delicacy in Italy and other Latin countries) as tripe.  It is used to make a delicious soup, for those who have the gumption to taste it...
14_suspend_in_water_P5160005 (-1x-1, -1 bytes) 13)  Let the pieces of abomasum soak in cold acidified whey over night in the fridge.  (For instance, use the whey left from making ricotta.)
6)  This is a close up of the omasum (lower center).
the reticulum is above, the abomasum is to the left, and a small portion of the rumen is to the right.
15_sieve_out_pieces_P5160006 (-1x-1, -1 bytes) 14)  Remove the pieces of soaked abomasum by pouring through a sieve.
7)  Trim off all of the stomach chambers to leave only the abomasum.  Note the folds (plica) in its inner wall.
(Note: Wolfgang Pachschwöll of Austria, (see below) says leave intact, do not wash (it removes enzymes), and blow up like a balloon to dry.)
16_add_rennet_P5160007 (-1x-1, -1 bytes) 15)  Stir the extract of abomasum into inoculated, warmed milk (as in a basic cheese recipe.)
8)  Spread the  abomasum out on a screen (stainless steel, in this case), and sprinkle salt to cover. 17_clean_break_P5160029 (-1x-1, -1 bytes) 16)  For the conditions described here, a clean break was acheived in only one hour!

Here are some points of expert advice on making rennet from Wolfgang Pachschwöll of "Hundsbichler company Austria - producer of natural rennet", sent in response to my initial posting of this page. (Thank you very much Wolfgang!)

1) Do not thoroughly clean out the inside of the abomasum. The “slime” inside contains rennin. Therefore, also no washing nor squeezing.

2) Lightly salt the abomasum, store undried with 30% salt in a closed container to activate the enzyme over three months. (Pepsin, another stomach enzyme, is also secreted in the inactive form (pemsinogen), and activated by acid or enzymatic action.)

3) The traditional way to then dry the abomasum is to inflate it like a balloon and dry by hanging in a cool dark place.

4) Dissolving and activation of rennin occurs best in acid conditions at a cool temperature.

Based on these suggestions, during a subsequent cheese making, I placed a 1.0 gm piece of the dried abomasum in 50 mL of whey drained from ricotta (it therefore was both acid, and sterilized by the heating of the whey for ricotta). I placed the suspension in the refrigerator overnight. When I added the 50 mL to four gallons of inoculated milk, it coagulated in an hour! Made perfect cheese. I will post pictures of the rennin solution and the clean break I achieved soon.

Next time, I will use only 0.5 gm of dried abomasum/ four gallons of inoculated milk.

Finally, natural rennet such as this has more enzymes than just rennin. It also is said to contain lipase which, by hydrolyzing butterfat, enhances the flavor of the cheese.