WO1998030115A1

WO1998030115A1 - A method of continuously sterilizing pumpable food by means of high pressure

Info

Publication number: WO1998030115A1
Application number: PCT/SE1998/000003
Authority: WO
Inventors: Fredrik Innings; Paul Mellbin
Original assignee: Tetra Laval Holdings & Finance S.A.
Priority date: 1997-01-08
Filing date: 1998-01-07
Publication date: 1998-07-16
Also published as: SE9700031D0; AU5684398A; SE9700031L; SE508712C2; DE19881866T1; GB2336289B; GB9914830D0; GB2336289A

Abstract

The invention relates to a method and an apparatus for sterilizing pumpable foods by means of high pressure. The high pressure, approximately 5,000 bar, is achieved by the food being caused to rotate at high speed. The apparatus includes a rotor (1) with a through-going shaft (2) driven by an electric motor. Within the rotor (1) there are disposed product pipes (5) for the pumpable food. The product pipes have an axial inlet (3) and an axial outlet (4) and they are disposed in one or more loops along the periphery (6) of the rotor (1).

Description

A METHOD OF CONTINUOUSLY STERILIZING PUMPABLE FOOD BY MEANS OF HIGH PRESSURE

TECHNICAL FIELD The present invention relates to a method of continuously sterilizing pumpable food by means of high pressure. The present invention also relates to an apparatus for carrying the method into effect.

BACKGROUND ART Foods of the type which is liquid or pumpable may, for example, consist of various dairy products, fruit juices, soups, sauces or desserts. To be able rationally to store and transport these products, they are normally sterile-treated, i.e. the product is subjected to high temperature for a given period of time. This sterile treatment has for its purpose to neutralise bacteria and deactivate the degrading enzymes which are to be found in the food. In that the product is sterile-treated and thereafter packed in an aseptic package, a product is obtained which may be stored at room temperature for a relatively lengthy period of time compared with the fresh, untreated food.

As good as all sterile treatment of liquid or pumpable food takes place today by heat treatment in various forms of heat exchangers, depending upon the product involved. UHT (Ultra High Temperature) treated milk is, for example, treated for a few seconds at 135-150°C. Products with a greater acidic content, such as fruit juices, are treated at 90-95°C during 15-30 seconds. Despite the fact that this treatment is, today, as gentle as possible and that the techniques for sterile-treatment of foods have made progress with the passage of time, it is unavoidable that thus treated food will have an inferior flavour as compared with the fresh food.

Attempts have long been made to find different methods of treating foods so that bacteria are destroyed and enzymes deactivated without changing or negatively affecting the flavour of the food. One of these methods is to treat the food at high pressure, i.e. 4,000 bar or more. Apparatuses for high pressure treatment of foods are described, for example, in German Patent Specification DE 42 42 311 and in Swedish Patent Application SE 9400705-1. However, both of these publications described apparatuses for more or less batchwise treatment of foods with pressure, and such apparatuses will, as a result, not be particularly efficient and will be expensive to run, since the pressure must be applied intermittently.

OBJECTS OF THE INVENTION

One object of the present invention is to realise a method and an apparatus for treating liquid or pumpable food with high pressure, which may be run continuously. As a result of the design of the apparatus, there will moreover be realised a treatment method which is considerably more economical to run than the prior art apparatuses for sterilizing foods using high pressure.

SOLUTION

This and other objects have been attained according to the present invention in that the method of the type disclosed by way of introduction has been given the characterizing feature that the high pressure is achieved by the food being caused to rotate at high speed.

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 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 side elevation of the apparatus according to the present invention, partly in section; Fig. 2 is a section taken along the line A-A in Fig. 1; and

Fig. 3 shows a table with the relationship between the radius of the apparatus and its speed of revolution.

OUTLINE OF THE INVENTION The principle for the method according to the present invention is, by subjecting the product to powerful rotation and associated high g forces, to achieve such a high pressure that the product, i.e. the pumpable food is sterilized.

To calculate the pressure that is required to sterilize foods, use is made of the following formula: P=ω² r²/ 200, where P is the pressure expressed in bar, ω is the speed of revolution in radians/ second and r is the rotation radius expressed in metres. To be able to achieve a satisfactory sterilization of the pumpable food, a pressure of approximately 5,000 bar is required during a time interval which varies from one product to another. A common stay time is approximately 5 minutes. A pressure of 5,000 bar, which is achieved by rotation, corresponds to a g-force of approx. 2.10⁶. If one takes this pressure of 5,000 bar as a point of departure, the relationship between the rotation radius and the speed of revolution, here expressed in rpm, will be obtained as compiled in the Table in Fig. 3. In order to obtain a viable apparatus for carrying the method into effect, the preferred embodiment calls for a radius of 0.8 metres, which, according to the Table, gives a speed of approximately 12,000 rpm. The method may be carried into effect with an apparatus of the type illustrated in Figs. 1 and 2.

The apparatus according to the present invention in principle consists of a rotor 1 with a powerful through-going shaft 2. The shaft 2 has, in its one end, an axial inlet 3 for the product which is to be treated and, in its other end, an axial product outlet 4. The inlet 3 continues in a number of product pipes 5 which, almost immediately after the inlet 3, are deflected out towards the periphery 6 of the rotor 1, to the desired rotation radius which, in the preferred embodiment is 0.8 m. The product pipes 5 continue inside the periphery 6 of the rotor 1 until they reach the outlet end of the rotor 1. Here, the product pipes 5 are deflected towards the centre line 7 of the rotor 1, and the product pipes 5 have their continuation in the axial outlet 4.

The length of the rotor is decisive of the capacity of the apparatus, which implies that, as an example, a rotor 1 with a radius of 0.8 m and a speed of revolution of approximately 12,000 rpm, and with a length of 0.5 m, will have a flow of 100 1/ h and an instantaneous product quantity in the rotor 1 of 8.3 kg. By extending the rotor, it is thus possible to increase the capacity of the apparatus.

The time interval when the product is located in the extent of the product pipes 5 along the periphery 6 of the rotor 1 constitutes the stay time of the product in the apparatus. In order to be able to achieve the requisite stay time for reliable sterilization, the length of the rotor 1 may, on the one hand, be extended, and the product pipe 5 may, on the other hand, be caused to extend back and forth along the periphery of the rotor 1, as shown in Figs. l and 2.

Because the product is led axially into the outlet 3 and removed from the apparatus axially, a complete pressure recuperation will be achieved, which implies that no power output is used for the pressure increase itself. An apparatus in which the rotor 1 has the dimensions r = 0.8 m and the length of the rotor 1 is 2.6 m, could thus be run by an electric motor (not shown on the Drawings) which has a power output of < 10 kW.

The high pressure on the product, and thereby the large g-forces to which it is exposed naturally place extreme demands on the materials from which the rotor 1 is manufactured. The design of the product pipes 5 is also affected by the pressure. The product pipes 5 should therefore have a relatively slight diameter of approximately 5-10 mm. They should furthermore be manufactured from a stainless material, since the treatment of foods places extremely high demands on hygiene. The pipes 5 should also be capable of being washed after the treatment process. Since the product pipes 5 are exposed to severe pressure stresses, attempts should be made as far as is possible to avoid joints in the pipes 5 and to ensure that any possible joints are placed such that they are not subjected to the absolute maximum pressure which is generated in the apparatus.

The rotor 1 may be manufactured from carbon fibres or amide fibres, so called Kevlar®. By utilising the structure of the material with its fibrous form, it is possible to orient the fibres radially in the proximity of the shaft 2 of the rotor 1, where the tensile forces to which the material is subjected are at their greatest. Further out towards the periphery 6 of the rotor 1, the fibres are suitably wound round the product pipes 5. By placing the product pipes 5 in circle segments 8 of the rotor body, or circle segment-like parts thereof, a more stable construction will be obtained. A rotor 1 which is rotated at high speed has a tendency to break up into circle segment-like parts. The space (if any) which occurs between the circle segments 8 should, as far as possible, be filled with rotor material, i.e. carbon fibre or the like. In order to reduce the air resistance on movement of the rotor 1, the entire periphery 6 of the rotor 1 should be encapsulated so as to obtain a uniform outer surface of the rotor 1.

The apparatus according to the present invention operates continuously, i.e. product is fed continuously under normal transport pressure into the apparatus via the inlet 3 in the shaft 2 of the rotor 1. The product may consist of a liquid or pumpable food, such as dairy products or fruit juices. Products containing particles may also be treated in the apparatus, but this is limited naturally by the diameter of the product pipes 5.

As a result of the rapid rotation of the apparatus, the product is forced, under centrifugal acceleration, out towards the periphery 6 of the rotor 1. In that new product is continuously fed into the apparatus, the product is forced further in the product pipes 5 which run along the periphery 6 of the rotor 1 in one or more loops. During that time when the product is located close to the periphery of the rotor 1, it is subjected to a pressure which, in the loop or loops which are located most proximal the periphery 6, amounts to 5,000 bar. The time interval constitutes the stay time of the product. The stay time is needed in order to obtain a sufficient destruction of bacteria and in order that degrading enzymes be deactivated. The stay time varies from one product to another, but is normally approximately 5 minutes. After the requisite stay time, the product is once again forced in towards the centre line 7 of the rotor 1 and departs from the apparatus through the outlet 4. The product is at slightly lower pressure than at the inlet to the apparatus, because of the usual pressure drop in conduits and pipes.

As will have been apparent from the foregoing description, the present invention realises a method and an apparatus for treating liquid or pumpable foods with high pressure, the pressure being so elevated that the food is sterilized. The apparatus and the method are continuous and are considerably more economical to run than corresponding batchwise treatment processes of food products. The present invention should not be considered as restricted to that described above and shown on the Drawings, many modifications being conceivable without departing from the scope of the appended Claims.

Claims

WHAT IS CLAIMED IS:

1. A method of continuously sterilizing pumpable foods by means of high pressure, characterized in that the high pressure is achieved by the food being caused to rotate at high speed.

2. The method as claimed in Claim 1, characterized in that the food is, by centrifugal acceleration, subjected to a pressure of at least 5,000 bar.

3. The method as claimed in any of the preceding Claims, characterized in that the food is caused to rotate in an apparatus to which the food is fed in axially; that it is flung out towards the periphery of the apparatus; and that the food departs from the apparatus axially after a certain stay time.

4. An apparatus for continuously sterilizing pumpable foods by means of high pressure, characterized in that the apparatus includes a rotor (1) with a through-going shaft (2), driven by a motor; and that product pipes (5), with both axial inlet (3) and outlet (4), are disposed in one or more loops along the periphery (6) of the rotor (1).

5. The apparatus as claimed in Claim 4, characterized in that the loop or loops of the product pipes are disposed in circle segments (8) surrounding the shaft (2).

6. The apparatus as claimed in Claim 4 or 5, characterized in that the rotor (1) has a radius of 0.8 metres; and that it is disposed to rotate at approximately 12,000 rpm.

7. The apparatus as claimed in any of Claims 4 to 6, characterized in that the body of the rotor (1) is manufactured from carbon fibres; and that the product pipes (5) are manufactured from stainless steel.

8. The apparatus as claimed in any of Claims 4 to 6, characterized in that the body of the rotor (1) is manufactured from amide fibres; and that the product pipes (5) are manufactured from stainless steel.