What is Rennet and How Does It Form a Curd?

Photo Credit: New England Cheese Making Supply Company

What is Rennet and How Does It Form a Curd?

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We’ve talked about Rennet numerous times on CheeseDigest before. Rennet is a very important aspect of the cheesemaking process and is a component that has a lot of influence over how your cheese turns out.

What is Rennet?
Rennet is an animal or vegetarian product that contains a complex assortment of enzymes which coagulates milk and therefore turning it into solids and liquid in the form of curds and whey.

As mentioned, there are two types of Rennet, Calf Rennet and Vegetarian Rennet. Calf Rennet comes from calves, specifically from their stomach. Vegetarian Rennet derives from a variety of different plants that all have the same properties to coagulate milk.

What Rennet is Best?
When it comes to vegetarian and calf, it’s all up to individual preference and if you want to ensure that your cheese is vegetarian or not. We have tried a variety of different Rennets that all produce very similar results. We tend to purchase our Rennets, along with most of our cheese products on Amazon because they have fast delivery and tend to have the best prices around as well.

Creating the Curd
The process of adding the Rennet to your milk is what will start the process of your curd forming. There are a few different methods when it comes to adding Rennet. That being said, regardless of how it’s added, it’s all done to achieve the same results, a good, firm curd.

Some recipes will tell you to add the Rennet straight to the milk and culture mixture, while others will have you do additional steps prior to adding.

How Long Does Rennet Last?
Rennet can last quite a while and can still be used most of the time after the recommended shelf life. However, you should expect that the strength of the Rennet will drop after the expiration date so you should plan on using more.
Animal Rennet
Up to a year
Vegetable Rennet
4-6 months
Organic Vegetable Rennet
3-4 months
How to Use Rennet
Your cheese recipe will specify how you should use your Rennet for that particular recipe, but we normally find that diluting the Rennet in 3.5 tablespoons of boiled water that has been cooled. After diluting it, simply pour the Rennet into the milk mixture.

Diluting the Rennet prior to adding it to the milk seems to help the Rennet milk better and more thoroughly with the milk.

Some other recipes are known to having you mix your Rennet with salt prior to adding it to the milk too.

Once your Rennet is added into the milk, regardless of how it’s achieved, you will normally have to stir the Rennet to help it combine with the milk mixture. Some recipes will specify what technique to use when stirring such as up and down motions or for how many strokes.

After stirring, Rennet needs to have time to sit and rest. This is the time that the curds start to form. It’s definitely a satisfying result when you start to check on your mixture and see your curds starting to form.

As you get more experienced in the cheesemaking process, the flocculation method is definitely something you should look into as it’s a much more accurate, but a lot more complex method. With this method, you may have to leave your curd to rest and set for longer than what your recipe states since different conditions can affect how long it takes for your curd to form.

Testing the Rennet Curd
To test to make sure the curd is ready to be cut, you need to check to see if it has a ‘clean break.’ This means that when running your finger or a curd knife, the curd will split cleanly. If the curd is mushy and falls back around the cut piece, you do not have a clean break yet and the curd will need to set for longer.

If you do have a clean break, you should see that the whey will be clear and start to pool around the break of the curd.

For a more in-depth look at easy cheese making with rennet watch this video


You can learn more about cutting the curd and more about curds in general by checking out the posts:

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