What Is Rennet? How To Add Rennet To Achieve A Curd

This post is Part 3 of the continued basic home cheese making instructions. See the Curd Nerd Beginner Page or the Basic Instructions category for previous parts.

We’ve talked milk, we’ve added the cultures. Now it’s time to set up a curd. Let’s add the Rennet.

What Is Rennet?

Rennet is a product that contains a complex assortment of enzymes which coagulates milk, turning it into curds (solids) and whey (liquid). Yes, Miss Muffet was eating cheese.

There are two types of rennet. Calf Rennet and Vegetarian Rennet. As suggested, the prior comes from calves, specifically their stomach. The latter comes from a variety of plants that have properties that coagulate milk.


I Trust and Use Renco Rennet

There are many suppliers and brands of rennet but I have to confess to using one of the cheaper options available – Renco Rennet.


What Is Rennet? How To Add Rennet To Achieve A Curd. Renco


The great thing about Renco is that it is reasonably priced but also, even though I normally but it direct in bulk, it is available at the supermarket so if I run out, it’s not a mission (or a delay) to get more.

Adding rennet to your milk, is what will set up your curd. There are a few slightly different methods for adding rennet but ultimately, you are trying to achieve the same thing each time.

A good firm curd. Some recipes will tell you to add your rennet straight into the milk.


How Long Does Rennet Last?

After the recommended shelf life the strength will begin to drop.

Animal Rennet

Up to 12 months

Vegetable Rennet

4-6 months

Organic Vegetable Rennet

3-4 months


How To Use Rennet

I always dilute my rennet with at least 50 mls of boiled and cooled water, and then pour the mixture into the milk. I feel it helps the rennet mix into the milk better. Other recipes will have you mix your rennet with the salt required in the cheese, before you add it to the milk.

Once your rennnet is in with the milk, different recipes will have you stir it in for varying amounts of time but in all cases you should stir top to bottom, and around the pot both ways to thoroughly mix the rennet in.

Then it’s time to leave it and wait for that wonderful moment when the curd is set. It can be nerve wracking waiting for that moment. Wonderful and satisfying when the curd sets, disheartening and frustrating when it doesn’t.

Each recipe, again, will have different set times and initially you should follow these as a guide.

As you get further down the track of making cheese you can start to work with the flocculation method which is much more accurate, but complex so I will explain it in another post.

You may have to leave your curd to set for longer than your recipe states as different conditions can affect how long it takes.


Testing The Rennet Curd

The test to know whether your curds are ready to cut is to check for a ‘Clean Break’.

Checking for a clean break means running a finger (a very clean finger) through your curd about 3cm deep and seeing if the curds cleanly separates and breaks away from the finger.

If the curd is mushy and falls back around the cut in pieces, you do not have a clean break and should leave the curds for longer to firm up.

If you have a good, firm curd you should find that when you cut the curd, and even during your clean break test, the whey will be clear and will start to pool in the break in the curd. See the Techniques page for point by point instructions.

You are ready to start cutting the curd!

In the Troubleshooting page I have listed a few reasons why you might not achieve a good curd.

This can happen to any and all cheese makers and as I say, can be very frustrating but if you know the reasons why it can happen, you can make sure you avoid as many of them as possible and increase the number of curds you get that are perfect.

I will talk more about this in future posts but in the meantime, good luck! I really hope I have explained simply what is rennet? And why it is used in home cheese making.


Do you have any questions or comments about using Rennet in your Home Cheese Making? Join the discussion over at the Curd Nerd Forum. We would love to hear from you!


Curd Nerd Forum

8 thoughts on “What Is Rennet? How To Add Rennet To Achieve A Curd

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  • 20/10/2012 at 6:00 am

    thanks, curd-nerd! i am waiting (rather impatiently) for my curds to hopefully set up and researching the heck out of why they might never. your site is my favorite! thanks for all of the great info!!!

    • 23/10/2012 at 11:31 am

      Hey Suzanne

      Thanks for you comment. I hope that your curds finally set up but if they didn’t, drop me another comment and let me know what they did. I’ll do my best to help you out for more success next time : )

  • 03/01/2014 at 8:01 am

    Do you just leave the milk with rennet out at room temperature?

    • 03/02/2014 at 4:02 pm

      Each recipe you follow should give you instructions on what temperature your milk should be retained at after adding the rennet, and for how long.

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