Advantages of UHT
The D and Z valves are higher for quality factors than microorganisms. The reduction in process time due to higher temperature (UHTST) and the minimal come-up and cool-down time leads to a higher quality product.
Long shelf life:
Greater than 6 months, without refrigeration, can be expected.
Processing conditions are independent of container size, thus allowing for the filling of large containers for food-service or sale to food manufacturers (aseptic fruit purees in stainless steel totes).
Both cost of package and storage and transportation costs; laminated packaging allows for use of extensive graphics.
Difficulties with UHT
Complexity of equipment and plant are needed to maintain sterile atmosphere between processing and packaging (packaging materials, pipework, tanks, pumps); higher skilled operators; sterility must be maintained through aseptic packaging
With larger particulates there is a danger of overcooking of surfaces and need to transport material - both limits particle size.
There is a lack of equipment for particulate sterilization, due especially to settling of solids and thus overprocessing
Heat stable lipases or proteases can lead to flavour deterioration, age gelation of the milk over time - nothing lasts forever! There is also a more pronounced cooked flavour to UHT milk.