DIY: Traditional Rennet

Warning: This post has a few photos that might bother some – internal organs just after being harvested. 

Although I’m a vegetarian in all other respects, I do eat classic cheeses such as Parmigiano Regianno and Roquefort, all of which are made with traditional rennet. I also butcher animals on our farm to feed my family. Included in that menu is the occasional goat.

Cheesemaking is a huge part of my life. I’m inquisitive nature and always wanting to learn more about all aspects of cheesemaking. One of those aspects that I had no experience with is the harvesting of a kid and production of natural rennet.

An opportunity presented itself while I was teaching a week long goat care class here at our farm and the attendees expressed an interest in learning how to butcher a goat. Athough slaughter and butchering are a very somber, intense, and private experience for me, I believe strongly in helping others learn not only how to do it properly, but that it can be a beautiful and educational experience as well.  The saying “every animal deserves a good life, a good death, a good butcher, and a good chef” is one of my favorites. So we selected a candidate, a two week old buckling. Not only would the students learn to butcher, but I would harvest the abomasum (the fourth stomach from which traditional rennet is made), our intern Amanda would tan the hide, and the entire

Baby ruminants are truly the first cheesemakers! These cheese curds were in the abomassum of a two week old kid.

Baby ruminants are truly the first cheesemakers! These cheese curds were in the abomassum of a two week old kid.

class would feast on roasted, suckling kid for our final meal.


I had read several accounts of how to harvest and make kid, calf, and lamb rennet. All of them varied and all of them stated that the curing time for the organ was anywhere from 6 months to a year. Hmm, why would that be, I wondered? The kid makes cheese curds immediately in its stomach, so it wouldn’t be for the sake of effectiveness. I believe now, but haven’t confirmed, that it might have to do with safety. The long pickling time might be to anticipate parasites or pathogens present in the organ. One of the students in the class told me that she had a Greek cheesemaking friend and would find out what he knew. Fortunately his recipe for kid rennet took only a few days of processing. The resulting rennet works beautifully!

I have made two varieties of our cheeses using the same batch to make one wheel using the homemade rennet and the rest of the batch with what I usually use. This way they will age side by side and any flavor differences will not be due to different milk or cultures. I’m still waiting for the cheeses I’ve made with it to age, but will report back to you on the flavor comparison. One of the cheese types I made usually uses purchased traditional rennet and the other microbial. So it should be quite interesting to compare. I can’t wait!

The abomasum is on the left in this image.  The esophagus can be seen at the bottom and the intestines at the top right

The abomasum is on the left in this image. The esophagus can be seen at the bottom and the intestines at the top right

The inside of the abomasum is covered with gentle folds of skin

The inside of the abomasum is covered with gentle folds of skin











Instructions for making kid, lamb, or calf rennet

  1. Harvest the abomasum of a kid, calf, or lamb under two weeks of age is ideal
  2. Rinse with non-chlorinated water, but don’t scrub
  3. Weigh the abomasum and place in jar.
  4. Add 12-15% salt and enough water to cover
  5. Let set at 65-70F for 24-36 hours
  6. Remove from the salt brine and shake off.
  7. Hang to dry in a cool room (no warmer than 70F) and dry until hard – depending on size 1-2 weeks.
  8. Weigh then cut into thin strips and place in food processor or run through a meat grinder.
  9. Slowly add 8 parts non-chlorinated water and process or use mortar to grind into a slurry or paste.
  10. Pour through a fine cloth, pressing with a spoon to extract as much liquid as possible.
  11. Add 4-5% salt by weight
  12. Keep in fridge.
  13. Use about ½ tsp (2.5 ml) per gallon (4L) of milk (you may have to adjust amount,  milk at 95F should coagulate within 10 min.)
  14. Lasts about six months in fridge.
The abomasum after drying

The abomasum after drying

Straining the rennet paste and brine after processing in food processor

Straining the rennet paste and brine after processing in food processor

During storage in the fridge, the whitish portion separates quickly from the salt water. I’m gently agitating mine periodically and for sure right before using. When used at the recommended ½ tsp (2.5 ml) per gallon (4L) of milk, our milk flocculates in under 10 minutes. So likely a bit less of the mixture is needed. So far, the strength hasn’t changed, but it’s only been six weeks since it was harvested and the processing begun. The strength could be checked before use using the steps in my book, Mastering Artisan Cheesemaking, for testing rennet (page 47) to better calculate the dosage before using.

The kid I harvested was exactly two weeks old and hadn’t yet started to chew his cud. This is ideal, however younger would mean an even higher proportion of chymosin to pepsin (the best natural rennets have at least 95% chymosin). Older animals will have increasing amounts of pepsin that will still coagulate milk, but can lead to bitterness in aged cheeses. Our kid was half Nigerian Dwarf and half Lamancha, so not a very large animal. The abomasum yielded about ½ to ¾ of rennet liquid after processing (I forgot t.o measure it before I used some!)

The Greek cheesemaker, who makes barrel aged feta in Greece and who now uses industrially produced kid rennet, says his cheese hasn’t been as good since he switched. It’s a shame when concerns over food safety also remove aesthetic diversity and opportunities for cheesemakers to craft unique products.  I’m actually not sure what would be involved to legally be able to use “small batch” rennet. Certainly the animal would have to be slaughtered at a USDA facility, but I imagine the process steps would also have to take place in an inspected facility with a meat processing license. Oh well, that doesn’t have to stop any of you from trying this at home!

I recommend Adam Danforth’s book Butchering for an even more in depth, artisan approach to harvesting meat.


23 thoughts on “DIY: Traditional Rennet

  1. this is so neat!
    i’d love to harvest my own rennet and, attend an artisanal butchering class–we have two ram lambs that we are planning to butcher some time in September. (too late for rennet though)
    we were going to hire a local salumiere/ butcher, but would love to learn to do it on our own–

  2. I have an abomasom curing in my pantry. I’m doing the cure for a year method, packed in salt. The little buckling died of trauma from his dam at about 36 hours and I donated him to a necropsy class and the instructor saved his abomasum so I could try this out. Looking forward to seeing how well it goes.

  3. Long ago i was given a bunch of Italian cheese “recipes” (more like descrptions with little in terms of instruction and next to no measurements or tempratures.)

    One of the recipes called for rennet made from the intestine of a kid. I have struggled for years to find any information on intestine rennet or how to make it. Its a shame cause the recipe I got is a cheese is on the verge of being lost to my understanding. It was produced similarly to tuma persa except it washed with wine and then stored in grey ash from the hearth on shelves in a basket in the cellar.

  4. Dear Gianaclis,
    I have read your diy-guide with great joy, and are very gratefull that you will share your experiences. I decided to try it out. At first we had a calf that had milk up until 6 months (and hay ect) so we decided to give it a try, even thought the chymosin level might be at only 75% (at least what I have read). Today I took the stomach out of the salt brine (after 36 hours) it smelled really bad, but I’m not sure exactly what to expect. It seems like it might be the because of the fermentet hay. We tried to rinse it off, but maybe it still changed the smell of the stomach compared to a stomach that has only had milk inside? Do you have any experiences in this, or any good advise?

    • Hi Ann, thank you for your kind words! What a great question too. I have never been able to get rid of the stink, BUT it doesn’t mean that it will come through in the cheese. But I’m not sure! The more important thing is that the amount of pepsin, as you’ve indicated you understand, might make the cheese bitter. I’ve tried to prepare tripe various times, and that fermented, methane stench just doesn’t go away. I think for the cultures that enjoy tripe, it must be an acquired taste. I’m sorry I don’t know the answer for the cheese, though! I would dry it and then experiment with a fresh set curd so that you don’t waste a long aging process.

      • It will come through some. It is actually slightly desirable depending upon the cheese. Tetilla is one such cheese. A product of spain and DOP protected. The bame means small breast due to its pointed pear shaped cone. Creamy smooth and even spreadable cheese bitter and buttery at the same time. It matures 10 to 30 days and requires stewing (also called cheddaring) where the cheese in its mold is subjected to high tempratures and humidity to expell its whey.

        stufatura is the italian name…most people at home do it by using an oven that is off along with some water under it in a pan for about 2 hours flipping the molds every half hour. Its a type of ripening process. Then a the 10-30 day aging comes into play. Though it requires cows milk with at least 25% fat content to do…

        Don’t have a full recipe but it would be a good use for it in a cheese where bitterness is ok.

        As for the smell that is normal. However when hung to dry should it develop anything other then white or green mold chuck it.

  5. Thank you so much for your replies. It helped a lot!!! Now only few days later the smell is much better. We also had a 2 days old calf that died, so now we have a little experiment going on. 6 months versus 2 days. It will be interesting to see and taste the differences. Thanks again.
    Best regards Ann

  6. Hi Gianaclis (and others!)

    I am trying to work out what yield (kg or equivalent) of Rennet I can expect from what input (kg or equivalent) of animal stomach – would be useful to know this for different animals.

    I understand this may vary considerably, but a rough idea of the expected yields and how this might vary would be amazing.


  7. Silly question – but do you keep the paste or the liquid brine after you strain it??
    Wasn’t clear (to me)
    Thanks !

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