Milk is an emulsion of fats and water of animal origin that contains sugar,
proteins, non-protein nitrogen substances, mineral salts, vitamins and numerous
enzymes. Right from the beginning of time, mankind has consumed preferably cow
and sheep’s milk, and on a lesser scale goat’s milk. The chemical composition
of milk depends on the animal species. When one speaks of “milk” generally cow
milk is intended.
The milk we find on sale is standardized in terms of fat contents,
homogenized, pasteurized or sterilized. The thermal treatment of pasteurization
brings milk to a temperature of around 72°C for at least 15 seconds.
The UHT treatment (Ultra High Temperature) is a particular sterilization
technique which consists in treating homogenized milk and pre-heating it to at
least 135°C using overheated water steam for no less than one second. UHT is
addressed as an indirect system when the sterilization of the milk occurs
through a heat exchanger, whereas direct UHT is when the sterilization of the
milk occurs in direct contact with the warming fluid (the water steam). Milk is
then cooled at environmental temperature and packaged under aseptic conditions.
In China, the government is launching a campaign to promote milk consumption
during childhood (preschool years) that could have an important impact on
worldwide consumptions in the long term.