When buying milk in the supermarket, there is a wide choice. Two important types are fresh milk, that has a short shelf life and needs to be stored in the fridge, and long shelf life milk, that can be stored at room temperature. Different countries prefer different types of milk. Why does this difference exist? And does the type of milk make a difference to its quality and nutritional value?
The main difference between these types of milk is the temperature used during processing. For fresh milk, a mild pasteurisation is used, with temperatures around 72°C. This way, pathogenic bacteria are killed, making the product safe for consumption. Bacteria that can spoil the milk are however not killed, making it necessary to store the milk in the fridge. For long shelf life, ultra-high temperature (UHT) treatment is commonly applied, with very high temperatures (130-140°C) for seconds. This treatment kills all bacteria that may cause spoilage. This milk has a very long shelf life and can be stored at room temperature, because bacteria can no longer spoil the product. The advantage of UHT milk is that it does not require cooled transport/storage, making it easier for dairy companies & retailers to work with.
But why then do we not just sterilise all milk, if it makes life easier? This is mainly due to taste. Pasteurisation has only a very limited effect on taste compared to raw milk. UHT sterilisation, on the other hand, causes the formation of a specific flavour due to the high temperature used.
And what then about the nutritional value? The main nutrients in milk (protein, fat, lactose, minerals) are not harmed by UHT sterilization, keeping them intact. For some vitamins, small reductions (max 10%) can occur. So the nutritional quality is essentially the same. Only when sterilisation is more intense, which can be noticed through a brown colour, the nutritional value is lower, due to damage to the protein (essential amino acids).
I earlier wrote about raw milk (link) and the immunoprotective components in them. Those components are more harmed by UHT sterilisation than pasteurisation, although health benefits for consuming these components is currently very limited, especially in adults.
Summarizing, the main differentiation between fresh & UHT milk would be on taste and shelf life, whereas nutritionally these products are virtually identical.
Kasper Hettinga, August 2017
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