What is Rennet?
Rennet is an essential part of traditional cheese making. It is a complex mixture of enzymes that helps cheese to coagulate, forming a solid mass – the curd. Rennet used to come from the stomach linings of cattle, but today it’s mostly produced through fermentation by factories, and various different types are available for purchase.

How Rennet Works
Rennet is made up of enzymes which react with proteins in milk to coagulate it. The proteins, collectively known as casein, are naturally present in milk and are the basis of cheese. When cut or exposed to acid or other coagulants, the casein proteins form a solid mass which can be separated from the liquid whey. The whey can then be discarded or used for other products, such as ricotta.

Types of Rennet
There is animal and vegetarian (or vegan) rennet available. Animal rennet still comes from an animal, traditionally the stomach of a calf, kid or lamb. Microbial rennet is made in a lab through fermentation and is suitable for vegetarians. It is not suitable for vegans as it is made with dairy. Some vegan cheeses use vegetable-based coagulants like lemon juice or citric acid, but these will not produce the same texture as a traditional cheese.

Conclusion
Rennet is an essential ingredient in traditional cheese making. Its enzymes help the casein proteins in milk coagulate, forming the solid curd necessary to make cheese. Rennet comes in both animal and vegetarian forms, though it can be difficult to obtain vegetarian rennet. Many types of vegan cheese do not use rennet, but rely instead on other coagulants like lemon juice or citric acid. Despite its complexity, rennet does not complicate the cheese-making process, and understanding it can be an important step on the cheese-making journey.