Milk Quality and the Importance of the Cold Chain 

Milk is truly nature’s perfect food. As the only food for the young mammal it is virtually sterile when produced in the udder of the cow and full of energy and building materials necessary for growth. Milk contains all the essential nutrients in the right amounts for all the energy and nutritional needs of their young. This is also true for humans and milk form an important part of our daily diet. Table 1 shows the different nutrients of milk in comparison with different types of animals.

Table 1: Composition of the milk of different animals

Milk also contains many vitamins. Vitamins are organic substances, which occur, in very small concentrations in the milk. Vitamins are essential to normal life process. The best known vitamins in milk are vitamins A, B, C and D.

Because milk is such a wonderful food, bacteria also take advantage of its nutritional value. Bacteria are single-celled organisms that can multiply very rapidly.

When milk is secreted in the udder, it is virtually sterile, but because milk is nature’s perfect food, bacteria will always try to get into the milk. This is called infection or contamination.

Even before the milk leaves the udder of the cow, bacteria can infect the milk through the teat channel.

In the course of handling the milk on the farm during collection and transportation of the milk and even during processing of the milk at the factory, milk can be infected by various bacteria.

These bacteria will spoil the milk by using some of the nutrients in milk, e.g. milk sugar, to produce lactic acid, which will sour the milk.

Other bacteria found in milk are very dangerous and can cause serious illness like food poisoning. These bacteria are called pathogens and must be avoided and contained at all cost.

As one can see, bacteria are unwanted due to the spoilage of milk and the health risk for humans. It is also quite clear that it is virtually impossible to keep them out of the milk. It is therefore important to work as clean as possible to prevent large amounts of bacteria to get into the milk, and to prevent the bacteria to grow once it is in the milk.

One of the best ways to prevent bacteria to grow, is to keep the milk as cold as possible. This must be done through the steps of processing and distribution as soon as the cow is milked until we buy the milk and consume it. This is called the cold chain.

Different bacteria will grow at different temperatures. Figure 1 shows the classification of bacteria by their temperature preference.

Figure 1: Classification of bacteria by their temperature preference

The dangerous bacteria (germs) will normally grow at the higher temperatures (25ºC – 37ºC) and can cause illnesses like food poisoning while spoilage bacteria will grow at temperatures above 7ºC and will make the milk go sour or putrid.

When the cow is milked, the milk leaves the udder of the cow at a temperature of about 37ºC. At this stage we refer to the milk as raw milk. Bacteria love this temperature and will multiply most vigorously at this temperature. If raw milk is not chilled quickly to 4ºC direct after milking, the bacteria start to grow to great numbers and will spoil the milk.

At a temperature of 4ºC bacteria are in a state of sleep and will have a very low activity. As soon as the temperature is raised, the bacteria awaken and start to use the nutrients in the milk and multiply again.

Apart from nutrients and temperature, bacteria also needs time to grow. Figure 2 shows the effect of temperature and time on the growth of bacteria.

Figure 2: Effect of temperature and time on the growth of bacteria

We must therefor keep milk at unrefrigerated temperature (> 7ºC) for as short as possible periods.

Clover collects the raw milk as soon as possible after milking and takes it to their factories where the milk is processed. To assure that all the bacteria that can make you ill (pathogens) is destroyed, Clover pasteurizes all milk and then deep cool the milk. The milk is now called pasteurized milk and is protected from bacteria as far as possible by packing the milk in special hygienic areas into heat sealed cartons or plastic bottles.

Pasteurized milk is kept at a temperature below 4ºC for the total shelf life of the product.

To ensure healthy, safe and fresh dairy products, the cold chain must be maintained from farm to fork, starting with the milking of the cow at the farm through all the processes up to the consumer keeping the milk in his fridge. Remember the cold chain. Always keep dairy products below 4ºC.