Milk, milk quality and milk cooling


Milk is the name of a whitish fluid that the mammary glands of mammals results in. Milk for newborn mammals, the first nourishment. Milk of certain animals, especially cows milk was made, serves the people as food. In the EU, the word cow's milk meant by. In milk from other mammals milk is the name of the animal coupled to the word, eg sheep milk, goat milk, etc.

Ingredients (%) Cow Sheep Goat Horse Buffalo Human being
Water 87,5 82,7 86,6 90,1 82,0 87,2
Milk fat 4,2 5,3 3,7 1,5 7,4 4,0
Proteins 1,5 4,6 4,2 2,1 3,6 1,5
Carbohydrates 4,8 6,3 3,9 5,9 5,5 7,0
Composition of milk of various mammals.

Bacteria in the milk

Due to its specific composition milk is very sensitive for a contamination by bacteria. In the udder milk is first almost sterile. Via the teat end bacteria have the opportunity to penetrate and to infect them. These bacteria are generally harmless and there are relatively few, only a few thousand bacteria per ml. But in cases of bacterial udder infections (mastitis), the milk can be highly contaminated with bacteria and therefore unsuitable for consumption.

In the milk duct are always concentrations of bacteria, but the most are washed away at the beginning of milking.

Frequently occurring bacteria are:

  • Lactic acid bacteria
  • Butyric acid bacteria
  • Coliform bacteria
  • Rotting Bacteria
  • Propionic acid bacteria

Bacteria are single-celled organisms. They reproduce primarily by cell division. Depending on the temperature, the bacteria can double within twenty minutes. When the milk temperature increases to body temperature, the bacteria in the milk increases so fast that milk with initially little bacteria can quickly sour. It is important that on the one hand, the initial number of bacteria in the milk is as low as possible and on the other hand, bacterial growth is slowed down as much as possible by cooling the temperature of the milk quickly to at least below 10 ° C. The number of bacteria in one millilitre of milk is called the bacterial count. This count is controlled by the dairy and with too high values (from 100,000 / in general), the milk no longer meets the highest quality standards.

Infections on the farm

With the actions on the farm, milk is susceptible to infections by various microorganisms, especially bacteria. The extent of infection and composition of the bacterial population depends on the cleanliness of the environment in which the cow lives. And also on the cleanliness of the surfaces with which the milk comes in contact, such as the milking machine, filters, milk cooling tank, etc. These are often much larger sources of infection than the cow's udder.



Possible reasons for the increase of bacteria:

  • not milked carefully
  • poor cooling
  • no optimal hygiene
  • too little water during cleaning
  • no, or too little detergent
  • too low temperature of the cleaning water
  • not enough turbulence in the main disinfection
  • too short period of disinfection
  • dead spots, which are not accessed during disinfection
  • worn parts (e.g. liner)

A condition for the production of quality milk is optimal hygiene. It is of utmost importance that the growth of bacteria is limited to a minimum.


The temperature is the most important factor to influence the growth and reproduction of bacteria in stored milk. Bacteria can develop only at certain temperatures, and these temperatures vary from species to species. In general, the growth of bacteria in the milk is greatly reduced by cooling to below 10 degrees. Temperatures of about 4 ° C are necessary in order to nearly stop bacterial growth.

Not only the storage temperature is important, but the time that is necessary to reach the storage temperature (4°C) is of influence. Milk cooling tanks are designed specially to cool the milk quickly to 4°C.

Milk cooling

The cooling of milk on the dairy farm has two important reasons:

  • the control of bacteria
  • the extension of time that the milk can be stored on the dairy farm. It is there-for possible to store the milk production for several days, thus, the milk will be collected less often and milk transport costs are reduced.
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