BACKGROUND ART Milk is an extremely sensitive and perishable food which may readily be destroyed by bacteria or by being exposed to direct sunlight. The distribution of milk in tropical countries or over considerable distances may therefore be a problem. In such instances, fresh milk is replaced by milk with extended shelf life, such as aseptic milk or condensed milk. Milk may also be in short supply in those countries which lack their own dairy production. A shortage of milk may have various causes, such as climatic, demographic or cultural.

Recombination is an alternative method that may provide those regions or countries without access to fresh milk with a product which is reminiscent of fresh milk. The recombination implies a method of producing milk or food products containing milk from milk powder. The milk powder which is produced from milk by evaporation and drying is a product that can be stored for long periods of time without deteriorating.

Recombination entails that skimmed milk powder is mixed with water and fat to form a recombined milk. The fat is to be emulsified in the liquid, which is an energy-consuming process. By the addition of flavourings, sugar, stabilisers or the like, there will be obtained different recombined food products, with milk as the base. Recombination of milk or milk products usually takes place in batches or in semi-continuous processes. A feature common to most of these prior art processes is that water is added to skimmed milk powder, this is mixed and then the mixture is allowed to hydratise. Thereafter, molten fat is added to the mixture and the combination is caused to pass through a homogeniser in order to obtain a stable

product. The stability depends on the size of the fat globules and their distribution in the liquid.

Later developments can offer mixers of the Tetra Almix type, where all components in the recombined product are mixed in a mixing vessel and are caused to repeatedly pass through a mixer. The mixer, which is of the type which consists of a rotor and a perforated stator, mixes the milk powder, water and fat. The further treatment of the mixture thereafter follows conventional methods, i. e. the mixture is permitted to hydratise whereafter, most generally in connection with a heat treatment, it is homogenised in order to obtain a stable product. By including, in such a plant, two or more buffer tanks, the plant will be semi-continuous in operation.

OBJECTS OF THE INVENTION One object of the present invention is to realise a method which obtains a stable food product which does not need to be homogenised.

A further object of the present invention is to realise a specific fat globule distribution in the recombined milk product which is particularly suited for the production of certain food products.

Yet a further object of the present invention is that the method need not necessarily require a hydratisation of the recombined mixture.

Still a further object of the present invention is to realise a method which gives lower operational costs compared with conventional methods and which also reduces losses by reducing the number of method steps.

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 characterising feature that the rotation takes place at an angular velocity which exceeds 270 rad/s.

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

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS One preferred embodiment of the present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings, in which:

Fig. 1 is a flow diagram for reducing the method according to the present invention into practice; and Fig. 2 shows a mixer which is employed for carrying the method according to the present invention into effect.

The Drawings show only those parts and details essential to an understanding of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT Fig. 1 shows a flow diagram for reducing the method according to the present invention into practice, where the part enclosed by means of ghosted lines constitutes the method. For carrying the method into effect, use is made of a mixing unit 1 consisting of a mixing vessel 2 and a mixer 3 placed in the bottom of the mixing vessel 2. The mixing vessel 2 is preferably connected to a vacuum pump 4.

There are provided conduit connections to the mixing vessel 2, of which one or two connections 5 are intended for milk powder. The mixing vessel 2 being under vacuum, the milk powder connections 5 come from one or more powder silos (not shown). The milk powder connections 5 may also be employed for the addition of other dry components to the recombined milk product, such as sugar, flavourings, stabilisers or the like.

There is also a conduit connection 6 into the mixing vessel 2 for water and a conduit connection 7 for fat. The mixing unit 1 also includes a centrifugal pump 8 connected to an outlet conduit 9 for recombined product and to an inlet conduit 10 in order to be able to circulate the recombined product. The simplest embodiment of the present invention is shown in that the outlet conduit 9 partly consists of the broken line product conduit. In order further to simplify the plant, i. e. in that case when the intention is only to circulate the mixture across the mixing vessel 2, the pump 8 is not necessary. In this case, the mixer 3 serves as a pump.

The mixer 3 which is disposed in the bottom of the mixing vessel 2 is shown in detail in Fig. 2. The mixer 3 consists of a drum 11 connected to the mixing vessel 2. In the drum 11, there is centrally disposed a rotor 12 which is driven by an electric motor (not shown). The rotor 12 is surrounded by a stator 13. The stator 13 is provided with a large number of apertures 15. Alternatively, the stator is provided with a number of slots. The mixer 3 is also provided with an outlet 14 for the product which has passed through the mixer 3.

The mixing vessel 2 is filled with a predetermined quantity of water through the connection 6. The water must be of good quality and should be at a temperature of between 40 and 70°C. The water is caused to circulate through the mixer 3, the outlet conduit 9, the centrifugal pump 8 and the inlet conduit 10 back to the mixing vessel 2. An alternative is without the centrifugal pump 8, according to the above- described embodiment.

At the same time, milk powder and fat are dosed or metered into the water.

Milk powder arrives via one or more connections 5 from powder silos which are not shown on the Drawings. The milk powder is fed into the mixing vessel 2 because of the vacuum which is created in the mixing vessel 2 by the vacuum pump 4. In that the mixing vessel 2 is under vacuum, the air which is entrapped in the milk powder is evacuated. A minimised air admixture in the recombined product entails that it is not necessary to de-aerate the product later in the process. An excessive quantity of air in a dairy product increases the risk of scorching and burning-on in possible later heat treatment equipment. Minimised air admixture also ensures an optimum wetting of the powder and prevents lumps from being formed in the recombined product. Other dry ingredients, such as sugar, flavourings, stabilisers and the like, are added in this manner through the connections 5. The method may be employed for admixing a total solids of up to 75%.

The fat preferably consists of milk fat, but other types of fat, such as vegetable fats or oils may also be employed. The fat should be at a temperature above its melting point which, for example, for milk fat is >40°C. The fat is pumped by means of metering pump (not shown) into the mixing vessel 2 through the connection 7. The addition of powder and fat takes place until such time as the correct composition of the mixture is obtained.

In Fig. 2, the addition of powder is shown by unhatched arrows. The hatched and black arrows symbolise the mixture of the different components. The rotor 12 draws down water and powder into the drum 11 and, by means of paddles 16 on the rotor 12, the mixture is flung by centrifugal force out towards the stator 13. The apertures 15, or alternatively the slots, in the peripherally disposed stator 13 allow the passage of the mixture and it passes out from the mixer 3 through the outlet 14.

In that the mixer 3 rotates at high speed, an extremely good mixing of the powder and fat will be obtained. The mixer 3 being caused to rotate at an angular velocity which exceeds 270 rad/s, a stable, recombined product will be obtained. The

angular velocity co of the mixer 3 in rad/s is calculated according to the formula =rpm x 2g/60, where rpm is the speed of rotation of the mixer 3. Preferably, an angular velocity of >350 rad/s is employed.

Trials with viscous products such as ice cream mix have demonstrated that a further increased angular velocity (o gives an improved fat globule distribution in the recombined product without subsequent homogenisation. The value of dv5 (volume surface) is approx. 1 at an angular velocity @ which exceeds 550 rad/s. Products such as ice cream mix and desserts based on milk will obtain increased creaminess in a distribution of the fat globules in the recombined product corresponding dv5~1. Ice cream mix trials have been carried out with angular velocities cl) of 440 rad/s and 572 rad/s, whereupon the ice cream mix has been frozen to form ice cream. The ice cream has then been compared with conventionally produced ice cream and flavour panel tests have given the ice cream manufactured according to the method of the present invention were given full approval. The method according to the invention makes for the variation of the angular velocity o) depending upon product and the desired creaminess of the product.

Further trials with products of lower viscosity, such as consumer milk, demonstrate that an angular velocity m of approx. 600 rad/s gives a value of dv5~0. 7.

These trials give grounds for assuming that a further increased angular velocity will give d, values that correspond to conventionally homogenised consumer milk.

Those parts of Fig. 1 which are not enclosed within the ghosted line region show how the method according to the present invention may be included in a larger plant. By including two or more buffer tanks 17, the method may be rendered semi- continuous. The recombined product may then be circulated across one of the buffer tanks 17. On this occasion, the ghosted product line described above is not employed. At the same time, another of the buffer tanks 17 containing the ready- circulated product may be emptied for further handling in the process. A possible third buffer tank 17 may be employed for hydratisation of the recombined product.

The emptying of the buffer tanks 17 takes place through the outlet conduits 18 and the product is pumped further via a pressure-amplifying centrifugal pump 19.

The recombined product is first pumped to a cooler 20 which may consist of a conventional plate heat exchanger or alternatively a tube heat exchanger. The product is cooled to approx. 20°C, preferably with cold water. Thereafter, the

product is caused to pass a filter 21 for the removal of foreign matter that may have accompanied the milk powder into the recombining process.

The cooled, filtered product can thereafter be stored in one or more buffer tanks 22 until such time as the product is to be packed or alternatively further refined into a milk-based dessert or an ice cream mix. Alternatively, the product may, directly after the filter 21, be pumped further by means of a pressure-amplifying centrifugal pump 23, in the conduit 24, direct to a packaging station or to further refinement. The plant may also include some form of heat treatment, such as UHT treatment (Ultra High Temperature) for obtaining a product with extended shelf life or for pasteurisation in order to produce a fresh milk-like product of limited shelf life.

In the above-described plant, where the method according to the present invention has been employed, it will be apparent that the capital investment costs may be considerably reduced, in that the plant need not include all of the equipment which conventional recombination plants normally include. Thus, possible hydratisation tanks may be dispensed with. De-aeration vessels are no longer necessary and the pre-heating which takes place before homogenisation, as well as the homogeniser proper, are no longer needed for obtaining a stable, recombined milk product.

In those cases when it is desired to further refine the recombined food product, those substances which are necessary for producing, for example, an ice cream mix or a milk-based dessert have already been added in the recombination process. The method may also advantageously be employed for producing sweetened, recombined condensed milk. Given that the method affords a stable product with a specific fat globule distribution, there will be obtained a recombined product which imparts superior creaminess and flavour to the finished product.

As will have been apparent from the foregoing description, the present invention realises a method of producing a stable, recombined food product which need not be hydratised, de-aerated or homogenised. This gives a considerably lower capital investment cost for a recombination plant. Operational costs will be lower in that energy-consuming homogenisation is not necessary, and also that product losses are reduced in cleaning and product change, since the number of components in the plant is reduced. At the same time, a recombined product will be obtained which is particularly well-suited for the production of ice cream mixes and milk-based desserts.