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:
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 enzyme chymosin. 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.
Casein Proteins Coagulate
Milk is about 86% water but also contains fat, carbohydrate (mainly lactose), proteins (casein and whey), minerals and vitamins. Milk is an emulsion of fat globules and a suspension of casein micelles. These are suspended in the liquid phase of milk that contains dissolved lactose, whey proteins and some minerals.
The chymosin in rennet breaks down the kappa casein on the surface of the micelles changing them from being hydrophilic to hydrophobic. This causes them to aggregate together, trapping fat and water molecules in the developing curd. Further processing of the curd helps remove more water and compress the curd to form a solid cheese
Releasing the Whey
After separating curds and whey, further processing of the curds helps release more of the whey trapped in the network of micelles before it is drained away. The exact processing steps vary depending on the type of cheese. However, generally, the curds are captured, pressed and moulded to form blocks of cheese.
Historically, whey was considered a waste product of cheesemaking. However, growing concern over the environmental impact of its disposal encouraged research to better understand the properties and potential uses of whey. Increasing scientific understanding and technological advances have led to a wide range of uses for whey and established it as a valuable coproduct of the cheese industry.
Ripening the Cheese
Cheese is left to ripen, or age, in a temperature and humidity-controlled environment for varying lengths of time depending on the cheese type. As cheese ripens, bacteria break down the proteins, altering the flavour and texture of the final cheese. The proteins first break into medium-sized pieces (peptides) and then into smaller pieces (amino acids). In turn, these can be broken down into various, highly flavoured molecules called amines. At each stage, more complex flavours are produced.
During ripening, some cheeses are inoculated with a fungus such as Penicillium. Inoculation can be either on the surface (for example, with Camembert and Brie) or internally (for example, with blue vein cheeses). During ripening, the fungi produce digestive enzymes, which break down large protein molecules in the cheese. This makes the cheese softer, runny and even blue.
And there you have it, the complicated science behind cheesemaking!