How Is Curd Made?

At the moment when the rising acid condition of  milk is just right, mix in some rennet. Rennet contains the enzyme rennin, from the cells in the stomach lining of a calf. Manufacturers obtain rennet by processing the lining taken from the fourth stomach of calves.
Rennet acts as a catalyst, causing a chemical action in which the casein in the milk coagulates as an insoluble, visible curd. If the acidity of the milk is at the optimum level, the curd will become firm in about forty to fifty minutes, filling the entire vat with a solid mass. It is much like yoghurt in appearance.
The temperature at which rennet produces a curd that is best suited for many varieties of cheeses is approximately 86 degrees Fahrenheit. After the rennet has been stirred through the milk, stirring must stop, and the milk allowed to remain absolutely quiet while coagulation takes place.