Ultra-high temperature processing is a method used to sterilise liquid foods, such as milk. This involves a rapid heat process which heats the liquid to between 135-150°C for between two-to-five seconds, followed by rapid cooling and then sealing the liquid in hermetic packaging.
Pasteurisation is a common process in the production of fresh milk, whereby the liquid is heated to a specific temperature (usually around 72°C for 15 seconds) in order to kill harmful bacteria, but the UHT process goes one step further in destroying all the microorganisms and heat-resistant spores in a liquid. This has the impact of sterilising the liquid and creating a product with a prolonged shelf life that doesn’t require refrigeration.
UHT science explained
Although pasteurisation has been used to process milk for many years, UHT is not a new development, indeed the process is also known as ultra-high pasteurisation. The idea behind standard pasteurisation is to kill organisms such as Listeria, Salmonella and E.coli. These are naturally present in milk and can cause illness, so pasteurisation is a very necessary step in order to make milk a safe and appealing product for general market consumption. The objective of ultra-high temperature processing is slightly different however, even though it achieves the same thing as standard pasteurisation.
The extreme heat of UHT processing kills virtually all the bacteria in milk, this includes the potentially harmful bacteria but also the organisms which spoil the milk and reduce its taste and smell quality over time. With all these microorganisms removed the milk is effectively sterile, and therefore doesn’t require any preservatives or additives to prolong its shelf-life or improve its flavour, as long as it is very quickly packaged and hermetically sealed to retain this sterile state.
It is still necessary to very closely control the process however. The UHT processing operatives must be cautious that the milk doesn’t boil when the extreme heat is applied. This would cause chemical changes that would adversely impact on flavour and the nutritional content. So it is important that the right temperatures are hit, but also that they are only applied for a very short period, before the milk is rapidly cooled.
The benefits of UHT milk
- Shelf life – UHT milk can be stored at room temperature for between six-to-nine months before being opened.
- Convenience – The extended shelf life of UHT milk means it can be bought in bulk to eliminate emergency situations, and also means it can be stored external to the refrigerator.
- Health – The nutritional benefits of milk are unaffected by the UHT process, with the resulting milk still retaining high calcium, protein and B vitamin content. The UHT process also kills off all harmful bacteria.
- Sustainability – Removing the need to chill the milk means UHT milk can be produced, stored, transported and sold without the need for refrigeration, considerably reducing the energy demands on the supply chain.
So now that you understand the science behind UHT milk, try it for yourself and enjoy the benefits.