Fermentation
Alongside heating, fermentation is also used to extend the milk’s shelf life. Fermentation involves adding ‘good’ bacteria that do not make the milk go off, but actually extend its life. These bacteria also often give fermented milk a characteristic flavour.
Lactic acid bacteria are added to the milk while it is being heated. The lactic acid bacteria cause milk sugar (lactose) to be converted into lactic acid. The conversion of lactose into lactic acid is also known as fermentation.
Fermentation forms the basis for the production of butter, cheese and yoghurt. There are various types of lactic acid bacteria that result in different products and flavours.
Read more about the shelf life of milk and dairy products