When the milk is inside the cow's udders, there are only very few bacteria in it. But during and after milking the milk can get bacteria from the cow's feces, skin and from soil and dust.
There are many good nutrients in milk, such as carbohydrates, protein and vitamins. There is also water in the milk. Therefore, bacteria thrive well in milk. But by cooling the milk down, you can avoid that bacteria grows, for most bacteria cannot grow, when the temperature is below 5 degrees.
Farmers cools the milk down just after it has been milked out. And in the milk truck, picking up the milk and running it to the dairy, there is also cold.
Pasteurization and heat treatment
When the milk arrives at the dairy, it is treated with heat. It is called pasteurization. Where you pasteurize milk at a high temperature for a short time. In England all milk sold in the shops has to be heat treated. That way you can be sure that all disease bacteria has been killed.
Important that the milk is in the refrigerator
To keep milk in the fridge by not more than 5 degrees. Both in business and at home. If the milk is kept too warm, bacteria in milk will multiply and destroy the milk so it becomes sour. When milk is in the refrigerator, it can stay fresh for about 8 days. When the milk is opened, can only keep milk fresh for a few days. If it is there for a longer period of time, it may become sour.