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Ultra-high temperature processing (or UHT) is the partial sterilization of food by heating it for a short time, around 1-2 seconds, at a temperature exceeding 135°C, which is the temperature required to kill spores in milk. The high temperature also reduces the processing time, thereby reducing the spoiling of nutrients. The most common UHT product is milk, but the process is also used for fruit juices, cream, yoghurt, wine, soups, and stews. UHT milk has seen large success in Europe, 7 out of 10 Europeans drink it regularly.[1] Its largest manufacturer, Parmalat, had $6 billion of sales in 1999.[2] In the North American market, consumers have been uneasy about buying warm milk, and have been much more reluctant in buying it. To combat this, Parmalat is developing UHT milk in old-fashioned containers. A lot of milk products in the North American cuisine are made using UHT milk anyway, like McDonalds McFlurries.[3]
UHT milk has a typical shelf life of six to nine months, until opened. However, once contaminated, UHT milk spoils much more rapidly than pasteurized milk because all the lactobacillus in milk has been killed by the high temperature heat treatment. Many people believe that UHT products are inferior in quality to less-aggressively-pasteurized alternatives, but this is disputed by the manufacturers.
It can be contrasted with HTST pasteurization (high temperature/short time), in which the milk is heated to 72oC for at least 15 seconds.
Returnable containers
The basic features of systems using returnable containers are the collection of empties and washing prior to re-filling. Differences in operation times and capacities of the various machines involved make intermediate storage necessary. Storage of unwashed empties is normally essential and may extend overnight so that washing and filling operations can begin next morning before the day's supply of unwashed empties arrives. Storage of washed cans is permissible as they have lids but storage of washed bottles is extremely bad practice because they are unsealed and therefore liable to contamination. Normally storage must be provided for filled cans and bottles to give flexibility in the distribution arrangements. For pasteurized milk this must be refrigerated. The requirements are shown schematically in Fig. 4.
Bottle washing, filling and capping machines should be of matching capacity, otherwise the labour-intensive operations of decrating and crating, as well as unstacking and stacking, would have to be repeated unnecessarily. This problem does not arise with cans, since they are not crated and may be easily stored empty after cleaning.
The required storage area, both for empties and for product, depends on the operation schedule of the plant which in turn is affected by the relation between required dispatch capacity and the capacity of filling machines in operation. The inter-relations between these factors are shown in Figs 5 to 8. As can be seen, the required storage areas may differ considerably depending on the arrangement of working time, type of packaging and capacity of equipment. Although no attempt is made to present here precise examples of operation schedules, some particulars of the operations are indicated on the diagrams.
The type of liquid milk produced and the consequent selection of a packaging and distribution system constitutes in many instances an extremely intricate optimizing problem. The selection will have to satisfy the requirements dictated by existing economic limits, production and distribution efficiency, retailing objectives, consumer considerations and ecological aspects.Even when the decision on the packaging system has been well founded and made with due consideration to all relevant demands, the actual application may sometimes prove to be a failure for lack of competent supervision of its application.
For the purpose of this study the classification of processing and distribution systems of liquid milk - as in use at present - is shown in Table 1.
UHT Treatment
UHT is the abbreviation for treatment by ultra high temperature. In this method, milk is exposed to a brief, intense heating, normally to temperatures in the range 135-140 °C but for a very short time, a second or less. The treatment kills all microorganisms that would otherwise spoil the product. The process depends upon a fairly complicated sterilizer/aseptic filling design. The two stages of effective heat sterilization followed by aseptic filling represent an integral system. Frequently the packaging material for UHT milk is cardboard which must be chemically sterilized prior to the filling operation.
It is extremely fortunate that none of the major pathogens in milk form spores!
If that was the case, UHT milk would not be possible
Conventional Sterilization
This is the original form of sterilization which involves in-container sterilization usually at temperatures from 115-120°C for 20 - 30 minutes. Sterilization is a process which causes complete destruction of microorganisms and their spores. Commercial sterilization does not always meet this definition, because some harmless, heat resistant bacteria may still be present. The criterion for food sterility remains to be a process, which will ensure no surviving botulism bacteria or their spores. The common guideline is to use a multiple of 12 for the D (121°C)-value of C. botulinum, or its equivalent.