UHT treatment requires both a sterilizer and an aseptic unit (for packaging the product). It is used for low acid (above pH 4.6) products such as UHT milk, UHT flavoured milk, UHT creams, soya milk and other dairy alternatives. The same process is also used to sterilize prepared food, such as soups, sauces, desserts, tomato and fruit preparations, and baby food.
The birth of high heat treatment and canning as a means of preserving food began in France in the early 1800s. By 1839, tin-coated steel containers were widely in use. In the 1960s, building on this early food conservation technology, Tetra Pak pioneered its own continuous UHT process and aseptic packaging systems, and so kick-started the growth of the UHT milk segment.
In UHT treatment, the goal is to maximise the destruction of microorganisms while minimising the chemical changes in the product. That means finding the optimal combination of temperature and processing time for different types of food.
Tetra Pak offers two alternative methods of UHT treatment: direct or indirect. In direct UHT heating, steam is briefly injected into the product, and this is rapidly followed by flash cooling. The brevity of the treatment makes it possible to achieve very high product quality.
However, the process requires relatively high energy consumption compared to indirect UHT treatment. With indirect heating, the product does not come into direct contact with the heat source, but is instead heated using heat exchangers. What makes this method so cost-effective is that most of the heat energy can be recovered.
Commercially sterile food needs to be heated to a prescribed temperature for a prescribed time period. The specific temperatures and times depend on the food involved. Low-acid, liquid food products such as milk are more prone to microorganisms and pathogenic bacteria than high-acid products such as fruit juices.
UHT, or Ultra High Temperature treatment takes place in optimized heat exchangers before packaging. This process minimizes heat penetration problems and allows very short heating and cooling times, at the same time minimizing unwanted changes in the taste and nutritional properties of the product.