What Is Rennet Aggregation?

Rennet is a digestive enzyme complex extracted from the stomachs of milk-producing ruminant animals like cows, goats and sheep. It causes milk to curdle, or aggregate, forming solid curds and liquid whey. Rennet aggregation is central to the cheese-making process.

What Is Rennet?

• Since ruminant animals consume a large fibrous, plant-based diet, they have four distinct stomach chambers which allow them to digest food multiple times. The final chamber of the stomach is called the "abomasum"; when cut into pieces, salted and dried, this stomach chamber becomes rennet.

How Does Rennet Work?

• Adding rennet to milk causes the milk proteins, or casein, to clump together. These clumps are cheese curds. Various factors, such as temperature, enzymes activity and hydrolysis, can affect the level of rennet aggregation.

Calcium Chloride and Rennet

• Adding calcium chloride to the rennet and milk mixture affects the speed of rennet aggregation. Increased levels of calcium chloride increase the speed of aggregation and the firmness of the curds by decreasing the pH of the mixture.