Coagulation is the agglomeration
of suspended particles, and separates solids from liquids or vice versa. It is often used in milk
processing to separate the curd from the whey.
Field of application
Coagulation is used in cheese
production and in the recovery of casein from milk.
Technique, methods and equipment
Temperature is one of the key factors that influence milk curdling. The required temperature
is obtained by using either heat exchangers
or by direct injection of steam into the curdling vat. The temperature must be between 30 and 40°C.
Starters and other ingredients are added to the milk. These ingredients help determine the specific characteristics of the final product. Curdling is carried out in suitable vats or tanks, using one or both of the following methods:
- using enzymatic coagulants (animal or microbial rennet)
- using acidifying starters.
When enzymatic coagulants or acidifying starters are used, a casein jelly is formed which encloses the fat. The jelly will have different characteristics depending on which coagulant method is used. This is important for achieving the desired final production. The curd is produced by the separation of the whey, which is then gathered and sent for further processing as appropriate. To obtain further separation of the whey
(e.g. in order to obtain a hard or semi-hard cheese), another heat treatment is given to the curd, under stirring
at up to 40-53°C. For other kinds of cheese, such as mozzarella or provolone, besides the curd being heated at a higher temperature mechanical processing is also carried out to obtain the characteristic stretching/melting properties (organic acids are used to control the pH and to hold the curd at the right pH for the stretching properties to form).