Swiss Cheese: How to Make Rennet for Cheesemaking

Though some folks try to search for ways around using it, rennet is a crucial ingredient for coagulating milk into curds when cheesemaking. Clean, sustainable sources of rennet can be difficult to find for the home dairy but you can learn how to make rennet on the homestead. 

Anyone who has added cheesemaking to their homestead skill set will likely have heard the story of the very first cheese. Naturally, there are variations to the age-old tale, but if you imagine a nomadic wanderer with a refreshing milky beverage jostling around over the miles at his side in a vessel made from a dehydrated stomach, and when tipping it to their lips, finds that it had curdled into a chunky slurry, you’ve got the picture. In reality, I find it more likely that a young animal was harvested at some point and the curds were discovered in the stomach. And found to be quite edible.

Why Should You Learn How to Make Rennet? 

With the exception of direct acid or lactic acid coagulated cheese, most cheese recipes require rennet to make curds. Vegetable and microbial (fungus) rennet are weak and make for poorly set curds, while FPC (Fermentation Produced Chymosin) Enzyme rennet is a genetically modified organism (GMO). If you want to avoid GMO ingredients, and make cheese with a strong, reliable curd set, you will need to use animal rennet.

Animal rennet is made using one of the stomachs of baby ruminant animals that are less than a week old. Ruminants were created to digest their mother’s milk and, using an enzyme in their abomasum, turn the liquid milk into curds they are then able to digest. Once the baby (usually a lamb, kid, or calf) begins eating grass the enzymes weaken as the digestive system prepares for a grass-based diet. Unless labeled otherwise, most cheese is made with animal rennet.  

You won’t be homesteading livestock long before the realization that farming can be both gloriously rewarding and fulfilling as well as devastatingly tragic at times. If one of our goals in our animal husbandry is to fully honor and respect the lives of the beasts under our care, then one way we can do that is to be prepared to harvest them if they experience an untimely death. Butchers cannot process already dead animals and, of course, you can’t plan for accidents or attacks so are you prepared to harvest the animals yourself? Even if you don’t intend to regularly butcher, it’s a skill worthy of acquiring for an emergency. In this way, though they have little flesh, a newborn lamb, kid, or calf can be redeemed for cheesemaking through this skill should an accident or injury takes its life. 

And, despite how uncomfortable our society is with the thought, it is likely that male animals are one day destined for slaughter. Most males are not of breeding stock quality and will become a nourishing source of protein. The modern person’s ethical standard of an animal being used for food is purely subjective to the scale of its fluffy cuteness. Whether for meat or rennet, the animal is being put to good use for food. 

Cheddar Cheese: How to Make Rennet for Cheesemaking

How to Make Rennet for Cheesemaking (Stomach Paste Method)

DIY rennet using this method is fast and simple- you may even be able to make cheese with it in less than a week!

There are as many ways to make rennet as there are cultures throughout history that have eaten cheese. Some salt and dehydrate the stomach. Some brine the stomach before dehydrating. Some use the brine as rennet. Others inflate the stomach to dry, some stretch it. Or pack the dried stomach in salt, simply storing it in the freezer. One source said that Mediterranean cheesemakers will fill the rinsed stomach with milk and parch it in the sun, then use the white powder as rennet. What all of these methods have in common is a long drying time of up to a year.

When I decided to learn how to make rennet last summer I divided the abomasum into three pieces and experimented to discover which method I preferred. The first thing I learned is there is very little actual information available on how to make rennet. Most sources give the gist of the process and follow it up with a statement on how easily one can simply buy the rennet. In the end, I not only preferred the process of making “paste” rennet but it was the quickest and most reliable method. 

1.) Locate the abomasum from a ruminant animal less than one week old. Any older and you risk a weaker product that won’t set curds. It’s easier to locate the abomasum if you remove all of the stomachs together and identify each one. (See photos here.) It will be the largest of the stomachs. Each stomach is very distinguishable by the internal tissue. Not only will the abomasum have a mixture of cheese curds and milk inside, but the walls will look like large folds of silk. 

2.) Once you’ve removed the abomasum, thoroughly rinse it. Pat it dry with paper towels and weigh it in grams. 

3.) Measure out 15% of the abomasum’s weight in salt. (I used sea salt.) 

4.) Measure out 50% of the abomasum’s weight in room temperature water and stir in the salt to make a brine. Most of the salt should dissolve but it’s ok if some doesn’t. 

For example: 

  • 174 grams abomasum (100%)
  • 26 grams salt (15%)
  • 87 grams water (50%)

5.) Cover the abomasum with the brine and allow it to sit for 3-7 days. (Other methods using a fresh stomach in a brine indicated they could be left for much longer, months longer. But the Brine, Dehydrate, Soak in Whey method didn’t set curds for me while this quick method did. The point is, this is a variable timetable so if you don’t get to it exactly at the right time, don’t pitch it assuming it won’t work.)

6.) Dry the abomasum. If it is still in one pouch-like piece, you may cut it open to lay it in a single layer for quicker drying. You can lay it flat, perhaps on a cooling rack, in a very warm, dry place for a couple of weeks until it is fully dried. Be sure to cover it to keep flies off if it is summer. Alternatively, you may use a dehydrator to make quick work of it. I was worried the jerky temperature would be too warm so I didn’t go that hot. It took about 24 hours for it to be dry enough to break into pieces. On my second attempt, it took a little longer and I had to put some of the still pliable sections back in for a couple more hours. 

7.) Using a food processor, spice grinder, or blender, powder the dehydrated pieces. 

8.) Weigh the powder in grams. 

9.) The powder will be next mixed in whey at a 1:8 ratio. Weigh out 8 times as much whey as you have rennet powder. Stir it into whey to form a well-combined slurry. This can be fresh whey from your last cheesemaking, a whey brine used for salting cheese, or you can prepare ahead by leaving a quart jar of raw milk on the counter for several days until it clabbers (this is lactic acid coagulation!) Then you can drain the whey from the curds and use it. 

For example: 

  • 35 grams powdered abomasum
  • 280 grams whey

10.) Squeeze the slurry through a piece of cheesecloth, squeezing every last drop through. What’s left in the cheesecloth will be a dry wad of fibrous material. The liquid portion will be stored in a glass jar in the refrigerator to be used for making hard cheese. 

My total yield was 200 grams of rennet. 

Butter Cheese: How to Make Rennet for Cheesemaking

How to Test Rennet Strength

Whether you make your own rennet or not, it’s important to learn how to test the strength of your rennet. It’s far less heartbreaking to lose a gallon of milk when you aren’t sure if your rennet is good than five or more gallons! Testing rennet can be done by watching for the flocculation point. 

1.) Acidify one gallon of room temperature milk with 1/16th mesophilic culture. (I used MA 11) Thoroughly stir in the culture for 2 minutes and allow it to rest for 30 minutes. 

2.) Slowly stir in ¼ teaspoon of rennet for 30 seconds. 

3.) Test for flocculation: Place a plastic cap, top down, on the surface of the milk just after adding the rennet. If you flick it, it will glide across the surface. Set a timer for 8 minutes. Flick the cap again. When the milk has reached the flocculation point, the cap won’t budge when flicked. You may need to add additional minutes (try two-minute increments) and retest if the cap still moves across the surface. Check out the cheddar cheese recipe video for a visual demonstration of the flocculation test.  

Flocculation should happen between 10-15 minutes. If it takes less than 10 minutes you can adjust your recipe to use less rennet. If it takes longer you will need to use more rennet to achieve flocculation in that time range. (If you simply use the amount of rennet the recipe calls for and the rennet flocculates outside that range, your curds will either trap in too much or too little whey and your cheese may not have the correct acidity.) 

Of course, learning how to make rennet with so few instructions available led to a lot of trial and error which I’ve journaled on my Substack along with information (including detailed photos) on learning how to locate the correct stomach during butchering, as well as a comparison of the methods and results of my trials for those curious to learn more about the process. 

About the Author

Quinn and her family have been homesteading in Ohio for over 17 years, many of which she spent sharing their experiences and encouraging other homesteaders at Reformation Acres until 2018. Besides raising their main crop of 8 children, Quill Haven Farm revolves around the Queen of the Homestead, the family milk cow. In addition to cheesemaking and other home dairy, the cow also provides skim milk to fatten a few hogs every year, raise up a beef calf, supplement the feed for their flock of laying hens & broilers, and beautiful compost for their 14,000 square feet of organic gardens. You can find her writing these days on her Substack-

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How to Make Rennet for Cheesemaking :: Homesteaders of America
How to Make Rennet for Cheesemaking :: Homesteaders of America