The Science of Making Cheese

Cheesemaking is the controlled process of removing water from milk. This process concentrates the milk’s protein, fat and other nutrients and increases its shelf life. Cheesemaking is one of the earliest examples of biotechnology.

An ancient biotechnology

Cheesemaking is an ancient biotechnology that dates back to the domestication of animals. It is thought that it was probably first discovered by observing the accidental souring of milk and then pressing and salting the solid curd to preserve it for later consumption. Find out more about some early examples of biotechnology in our article on ancient biotechnology.

Cheesemaking principles

Cheesemaking involves coagulating the casein protein in milk and then separating the milk into solid curds and liquid whey. The liquid whey is drained away, and the curds are salted, shaped and left to ripen in a controlled environment.

Microorganisms are used in each step of this process and determine the flavour and texture of the final cheese.

Bacteria acidify milk

Acidifying (souring) milk helps to separate the curds and whey and control the growth of undesirable bacteria in cheese. Usually special ‘starter’ bacteria are added to milk to start the cheesemaking process. These bacteria convert the lactose (milk sugar) to lactic acid and lower the milk’s pH.

There are two types of bacteria used for this process:

• Mesophilic bacteriathrive at room temperature but die at higher temperatures. They are used to make mellow cheeses, such as Cheddar, Gouda and Colby.

• Thermophilic bacteriathrive at higher temperatures, around 55 °C, and are used to make sharper cheeses such as Gruyère, Parmesan and Romano.

Enzymes speed up coagulation

Some cheeses are curdled only by acidity. For example, paneer cheese is made using lemon juice to curdle the milk and cottage cheese is made using mesophilic bacteria. However, for most cheeses, rennet is also added to the milk after a starter bacteria. Rennet is a mixture containing the active enzymechymosin. Rennet speeds up the coagulation of casein and produces a stronger curd. It also allows curdling at a lower acidity, which is important for some types of cheese.