BACKGROUND ART The heat treatment of milk with a view to obtaining a commercially sterile product or so-called UHT milk (Ultra High Temperature) is a well- known phenomenon. To UHT treat the milk implies that it is treated at high temperature for a certain given period of time. As a result of the heat treatment, micro-organisms are destroyed and heat-resistant enzymes are deactivated so that a milk is obtained with a long shelf life at room temperature. A commercially sterile product may be defined as a product which is free of micro-organisms which may grow and multiply under prevailing conditions.

Producing a UHT milk and packing it under aseptic conditions in an aseptic package affords a number of advantages, from the points of view of both distribution and storage. In countries lacking a distribution apparatus and network which function under satisfactory refrigeration, a considerable advantage is to be gained in the employment of aseptic milk products which may distributed and stored at room temperature over a lengthy period of time.

However, all treatment of the milk, both mechanical and thermal, implies that the flavour of the milk may be modified. Today, most methods for UHT treating milk are so gentle that extremely slight flavour modifications occur, as compared with pasteurised milk which is treated at considerably lower temperatures. However, the art is still seeking for a further improvement of the flavour of UHT milk, while maintaining the requirement of the destruction of harmful micro-organisms.

Most dairies today treat the incoming milk in a similar manner, irrespective of whether the milk is to be further treated at high temperature, i. e. UHT treatment, or whether the milk is to be sold as a pasteurised product. This implies that the incoming milk, which is at a temperature of

4°C, is heated to approx. 55°C and separated, standardised and homogenised. Thereafter, the milk is pasteurised at 72°C for 15 seconds, or in similar time/temperature conditions. The milk which then is to be UHT treated for obtaining an aseptic product is treated further by heating to approx. 140°C for a period of time of approx. 4 seconds.

In connection with UHT treatment of milk, a certain instability in the product may occur, because of enzyme activity. This may also have a negative effect on the flavour of the finished product.

OBJECTS OF THE INVENTION One object of the present invention is to treat the milk as gently as possible in its pretreatment in order not to subject the milk to heat treatment or mechanical action unnecessarily.

A further object of the present invention is that the heating process take place at an elevated temperature for a short time, with retained destructive effect, which also contributes to a gentler treatment of the milk, with consequentially improved flavour qualities.

Yet a further object of the present invention is that the method include an enzyme deactivation in one or more stages in order to obtain a stable, aseptic product.

SOLUTION These and other objects have been attained according to the present invention in that the method of the type described by way of introduction has been given the characterizing feature that the heat treatment takes place at a temperature exceeding 135°C, and that the method also includes enzyme deactivation in one or more stages at a temperature of 55-70°C for 2-10 minutes.

Preferred embodiments of the present invention have further been given the characterizing features as set forth in the appended subclaims.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING One preferred embodiment of the present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawing, in which: Fig. 1 is a flow diagram of an installation for reducing the method into

practice.

DESCRIPTION OF PREFERRED EMBODIMENT When the raw milk arrives at the dairy, it is normally at a temperature of 4°C. The incoming milk may possibly be stored in buffer tanks, this storage taking place at maintained temperature. When the milk is to be treated, it is conveyed along a conduit 1 to a separator 2. The separator 2 may be conventional type, but, if it is not the intention to heat the milk before separation, a so-called cold separator 2 may likewise be employed.

The milk is separated according to the invention at a temperature of 4-15°C, for which reason a certain insignificant heating may take place before the milk arrives at the separator 2. Experiments have demonstrated that a certain, albeit negligible, increased fat content is obtained in the skimmed milk on separation at low temperatures. However, the advantage is that a gentler treatment of the milk will be obtained than is the case in separation at conventional temperature. A cold separator 2 differs in principle from a standard separator in that the distance between the panels is slightly greater, since cold cream is of a higher viscosity than the warmed cream.

Alternatively, conventional separation at approx. 55°C may be employed.

As a result of the separation, there will be obtained, from the separator 2, cream in one conduit 3 and skimmed milk in one conduit 4. Both the cream and the skimmed milk are at a continued low temperature of 4- 15°C, alternatively 55°C if conventional separation is employed. The cream is led in its conduit 3 to a standardisation unit 5 in which it is possible to obtain an exact proportion of cream for re-admixing to the skimmed milk, which gives a milk product with the desired fat content. The excess cream is led in a conduit 6 out from the standardisation unit 5 for separate treatment.

By separation and standardisation at a relatively low temperature of 4-15°C, there will be obtained a considerably gentler pretreatment of the milk which is to be further treated to UHT milk. Conventional dairy handling and pretreatment of UHT milk involves hot separation at 55°C and most generally pre-pasteurisation at 72°C for 15 seconds, or at similar time/temperature combinations. These heating operations imply an unnecessary temperature action on the milk which, in a later stage, is to be subjected to substantially higher temperatures with a view to obtaining a commercially sterile product.

The conduit 4 with the cream re-admixed into the skimmed milk is led to a UHT unit 7 of conventional type. The UHT unit 7 normally also incudes a homogeniser which is preferably placed after the heating of the milk, but which may also be placed ahead of the heating. The homogenisation is carried out in order to obtain a milk product where the fat globules are comminuted to small fat globules of equal size. If the milk is not homogenised, a cream precipitation will occur, i. e. the fat globules (which are lighter) accumulate in the upper region of the finished package. Almost all consumer milk is homogenised today.

The UHT treatment proper takes place according to the present invention in that the milk is heated to a temperature above 135°C for a brief period of time. Preferably, the heating takes place to 135-175°C for the requisite time, depending upon the requirements on destruction or on the food regulations in each respective country. The destruction requirement is dependent upon the bacteria and spore content of the incoming milk.

Experiments have demonstrated that a heating according to the present invention gives a product which satisfies the requirements of commercial sterility.

In a UHT unit 7 of conventional type, the heating of the milk may either take place directly by steam injection or steam infusion or indirectly by the milk being heated in some form of heat exchanger, or a combination of these methods.

In some UHT treatments of milk, a certain instability in respect of enzyme activity may occur. This instability as a result of enzyme activity also affects the flavour of the UHT product and the objective is to obtain a stable, aseptic product. According to the present invention, such instability may be remedied in that the milk, after the UHT treatment, is cooled in one or more stages at temperatures of between 55 and 70°C, in a time interval of between 2 and 10 minutes, for example 63-65°C for 4-8 minutes, whereafter the product is cooled to packaging temperature. The enzyme deactivation requires holder cells of tubular type or the like, which may be integrated into the UHT unit 7.

Alternatively, the enzyme deactivation may be carried out prior to the heat treatment. Deactivation prior to heat treatment takes place in a corresponding manner, in one or more stages at temperatures of between 55 and 70°C, in a time interval of between 2 and 10 minutes, for example 63-

65°C for 4-8 minutes. The enzyme deactivation takes place holder cells of tubular type or the like. A certain advantage by placing the deactivation ahead of the heat treatment is that this method step need not be carried out under aseptic conditions.

The ready-treated milk is conveyed in a conduit 8 further to one or more filling machines 9. The filling machines 9 are aseptic and may, for example, be of the type which packs the milk into parallelepipedic packaging containers of single-use disposable type.

The heating of the milk modifies the milk chemically, with the result that the flavour of the milk undergoes a change. Thus, the art is striving to achieve as slight a chemical action as possible on UHT treatment of the milk.

Flavour is a subjective factor, but by measurements of lactulose in the milk, it is possible to gain an indirect measurement of the effects on flavour. The higher the temperature loading to which the milk is subjected, the higher will be the level of lactulose content in the milk. Experiments in pretreatment and UHT treatment of milk according to the present invention have demonstrated that lower levels of lactulose content, and thereby indirectly an improved flavour of the finished UHT will be obtained.

As will have been apparent from the foregoing method of treating the milk, there will be obtained an aseptic product which, as a result of the gentle treatment, gives considerably improved flavour qualities.