Those new to the cheese scene may have heard the term ‘rennet’ without fully understanding what it means. Many myths and misconceptions about rennet are out there, but today we are going to cover some of the most common ones. So what really is rennet, why is it in your cheese, what’s true, and what’s not? Let’s take a closer look.
What is Rennet? Let’s Start with the Basics
In order to explain what rennet itself actually is and what it is used for, we need to start with the basics and cover the cheese-making process.
The Cheese-Making Process
Essentially, cheese-making involves turning a liquid into a solid. Of course, there is much more work involved, especially to create different flavors and kinds of cheese, but that is the foundation.
Rennet is used to coagulate the milk and help it solidify. Cheese-makers collect the milk they will use and add starter cultures. The starter cultures begin changing the lactose into lactic acid, increasing the acidity and starting to thicken the milk. Finally, the rennet is added. The rennet encourages curds to form, which are separated from the whey. The curds are then aged or processed to create the cheese. If you are curious about some of the methods used to create different types of cheeses, check out our article on rinds.
So, What Exactly is Rennet?
To explain what rennet is, we’ve got to use a little science-speak. Rennet is made up mostly of chymosin, which is an enzyme. Enzymes act as biological catalysts that can kickstart a process or change. Chymosin starts the process of solidifying milk. Rennet can be created or collected in four different ways, though all serve the same purpose.
The Four Types of Rennet
1. Animal Rennet
Usually referred to as ‘traditional rennet,’ this type of rennet was the original one used in cheese-making. The chymosin enzyme is collected from the stomach lining of calves, ewes, or kids (baby goats). Chymosin is used to help certain types of baby animals digest their mothers’ milk. The source of animal rennet is why some vegetarians are concerned about eating certain types of cheese.
2. Plant Rennet
Derived from cardoon, thistle, artichoke, nettles, and other plants, this rennet is not the most popular among cheese-makers as it can present some unique challenges.
The plants are soaked in water to extract a thickening enzyme similar to chymosin, which is then used to thicken the milk. Plant rennet’s strength is not consistent, so it is difficult to gauge how much cheese-makers need to use. It can also affect the flavor of the cheese. Some types of cheese capitalize on this.
Many Portuguese cheeses use thistle rennet to give their cheese a distinct flavor, like Torta del Casar, Azeitao, Serra da Estrela, and Serena. Most cheese-makers avoid plant rennet, though, as it can give the cheese a bitter or vegetable flavor.
3. Genetically Engineered (Fermentation Produced) Rennet
Genetically engineered rennet is produced in a lab. Here comes the science-speak again, just bear with us! Chymosin chromosomes are extracted from an animal’s stomach cells and implanted into yeast cultures that act as a host. New enzymes grow and are then separated and purified. These new enzymes are considered completely separate from the animal’s stomach cells. Genetically engineered rennet is very popular as it is so cost-effective and reliable.
4. Microbial Rennet
Some molds produce an enzyme that is similar to chymosin. Labs extract that enzyme and use it to create a rennet for making cheese. Microbial rennet can also make it easier for certain cheeses to be labeled organic or kosher. Plus, it has a much longer shelf life and is less expensive than animal rennet, allowing cheesemakers to produce cheese that’s more accessible to cheese loving customers. Cello Cheese uses microbial rennet, also commonly known as “vegetarian rennet,” in all of our cheeses so that those on a vegetarian diet can safely and confidently enjoy Cello cheese.
Fact vs. Fiction
Now that you have some background on rennet and exactly what it is, we can go over some of the common misconceptions surrounding it.
Fiction: Animal rennet is inhumane.
Fact: Animal rennet is harvested humanely. Animals that are already being sold and used for meat are then processed for rennet collection. This way, more of the animal is used so that ingredients and resources do not go to waste.
Fiction: There is no vegetarian rennet.
Fact: The other three types of rennet —plant, genetically engineered, and microbial— are all vegetarian. Even if strict vegetarians wish to avoid genetically engineered rennet, there are still cheeses created with plant and microbial rennet.
Fiction: Cheese-makers have to tell you what kind of rennet they used.
Fact: Unfortunately, in the United States, the Food and Drug Administration does not require producers or sellers to delineate between which rennet was used. However, a ‘kosher’ symbol means that animal rennet was not used to make that cheese.
Whether you are a vegetarian or just someone curious about cheese, hopefully, we have helped you understand more about how your cheese is made. Rennet is, most simply, an enzyme used to solidify milk. Now that you know more about where rennet comes from, you can make more informed decisions about your diet. Plus if you’re a vegetarian, you can still enjoy cheese.
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