Rennet 101

In the process of my short-ish (10 years) cheese making career, I learned much from my excellent teachers. Unfortunately, I also learned a few lessons the hard way. I try to blame it on my hair color, but that doesn’t really fly. One of these difficult lessons was, if you mess up adding the coagulant (or forget it entirely…opps.) you don’t get cheese. You just get this unusable milky stuff that has to be dumped down the drain. I thank the Lord even now, for such a gracious and understanding Uncle/Boss who never gave me a harsh word and reassured me of the lessons I could learn in that situation. And so, welcome to Rennet 101! Class is officially in session!


We use a microbial rennet for our Gouda, but some cheeses (such as our Paneer) use other kinds of coagulants. Basically something acidic to cause the milk to react and form little curds. Citric acid (lemon juice is common), vinegar (which is what we use for our Paneer), and tartaric acid are other options used in cheese making.


When I made cheese in our plant, rennet was this syrupy brown substance (think a true maple syrup “that-came-out-way-too-fast” consistency, not so much Mrs. Butterworths slow-as-tar thickness) responsible for turning milk into curd. Exact down to the millimeter, we stir it into a squeaky clean, ultra sanitized bucket of water to dilute it into more of a light amber color. Then, with the paddles spinning furiously, we pour the rennet into the huge vat of milk. The rennet stirs for exactly 2 minutes and 20 seconds before we halt the paddles, and let the milk rest for half an hour. This is when it does its magic and everything from there on out is decently simple…as long as you got the rennet correct.

This is my cousin Marlies, holding a Feta curd. She’s a good sport allowing me to plaster her beautiful face all over. 😉

This magic cheese making ingredient has four different types.

  1. Calf Rennet. Made from the (chymosin) enzymes found in a calf’s stomach lining, this is the original and most traditional type of rennet.
  2. Plant Rennet. This is where plants are soaked in water to extract a thickening enzyme similar to the one found in calves.
  3. Genetically Engineered Rennet. Since this one is a little more technical, here is a real definition of the process.

    “Chymosin chromosomes are extracted from an animal’s stomach cells then implanted into yeast cultures that act as a host. The host culture encourages the growth of new chymosin enzymes. The new chymosin enzymes are separated out and purified.”

    Sounds pretty scientific doesn’t it?

  4. Microbial Rennet. Enzymes similar to chymosin (the one found in the stomach lining of a calf), can be found and extracted from some molds to produce this type of rennet. This is the rennet we use to create our fabulous cheeses!

*Side note, if you read “mold” and thought “ew.”, mold is actually a good thing and very common in the cheese world! Cheese making strictly uses molds which are safe to eat, and are used often to produce unique flavors and aromas.

Various rennets produce different results in cheeses, so you have to know how to work with them. They tend to be a little touchy, hence the rennet being the most exact bit of cheese making. In my mind at least!


2 Replies to “Rennet 101”

  1. Thanks so much, I love cheeses, or anything that looks like cheese! Please post more of this type of information about your specific cheeses that you make, I’m a big fan if a small buyer! (due to $)

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