Separation and standardisation in liquid milk & cream production

The first separation process removes most of the cream and fat from the raw or whole milk, leaving skim milk. To achieve a better separation of the two components, the raw milk is typically warmed to 50 - 55°C. The separation takes place in a centrifuge, where the cream, being lighter, moves towards the centre. The skim milk is extracted from the top of the vessel through a concentric outlet channel.

The next stage is standardisation, which involves adjustment of the fat content of the skim milk, or other milk products, by the addition of more cream, or skim milk, as appropriate. The required fat content differs, depending on the desired product to be produced to meet customer demand. The cream and standardised milk leaving the separator normally have a constant fat content level, if all other relevant parameters also are constant: but seasonal fluctuations can occur. The control of the standardisation process in modern plants is computerised, for which flow and density meters, pressure and temperature sensors and various control valves are important. This control system also usually controls the inlet and outlet flows in the previous separation stage. The standardised milk is now homogenised. This has become a standard process, used to stabilise the fat emulsion against gravity separation. The milk, still hot is passed via a heat exchanger to transfer some of the heat to the incoming raw milk, and continues on to the pasteurisation stages.

KROHNE instrumentation is vital in the automation of the separation and standardisation process, using OPTITEMP temperature sensors and OPTIBAR pressure transmitters. The OPTIMASS straight tube Coriolis mass flowmeters measure the flow rate of the cream, and also measure the fluid density, which gives a precise measurement of the fat content of the milk and cream throughout the process. Accurate OPTIFLUX electromagnetic flowmeters ensure that the flows in and out of the separator are monitored and controlled.