GB2252230A

GB2252230A - Food processing apparatus

Info

Publication number: GB2252230A
Application number: GB9101994A
Authority: GB
Inventors: Derek Slater; Ichael Stephen Grace
Original assignee: APV Baker Ltd
Current assignee: SPX Flow Technology Crawley Ltd
Priority date: 1991-01-30
Filing date: 1991-01-30
Publication date: 1992-08-05
Anticipated expiration: 2011-01-30
Also published as: GB9101994D0; GB2252230B

Abstract

In a method and apparatus for cooling a pressurised food processing stream e.g. which has been sterilized, cooler liquor 14, which may form part of the finished product, is injected into the centre of the stream. A cooling jacket 6, 8 surrounds the stream, as is conventional. The rate of cooling can be significantly enhanced to avoid over cooking of the stream during the cooling process. <IMAGE>

Description

FOOD PROCESSING APPARATUS The present invention relates to food processing apparatus and in particular to a process and apparatus for cooling a pressurised food process stream containing particulate material.

The invention is particularly applicable to the sterilisation of particulate food material.

When a food product is sterilised by heat treatment, it is heated to the required temperature, held at the temperature for a specified time and then cooled. The required temperature and time are determined by the thermal death characteristics of the pathogenic spore predominating in the food product. It is preferred to cool the product as quickly as possible, otherwise over-processing may occur if the product is maintained at the relatively high sterilising temperature for too long.

When sterilising food products, the cooking value applied to the product can be defined by the following expression:

beginning of process where T = temperature /OC ref - reference temperature /OC, (often taken as 1000C) Z = the temperature change which gives a ten-fold reduction in the time required to give a ten-fold reduction in the number of spores in the product /OC t = time/minutes The prior art cooling apparatus for particulate food products (that is food particles dispersed in a liquid medium) is a tube-in-tube cooler, the product is passed through the inner tube and a cooling medium is passed through the outer tube. Heat transfer occurs across the wall of the inner tube.The rate of cooling with this system is slow, which results in a significant contribution to the cooking value during the cooling stage of the process.

The heat transfer mechanism of the prior art system relies on heat transfer from the centre of the process stream to the edge (the wall of the inner tube) and then to the cooling medium. In some cases, the viscosity of the product increases sharply with a fall in temperature and so a gel layer may form at the tube wall, which further inhibits cooling of the centre of the stream.

With particulate food products a large diameter pipeline is required (usually at least 73mm i.d. for the inner pipe) so that particles up to 25mm in size do not become blocked in the pipe work or associated valves. With liquid product streams, various mixing devices can be used to induce turbulent flow in the pipeline to promote the transfer of heat from the centre.to the edge.

However, this is not appropriate for particulate products because of the risk of damage to the particles.

A first aspect of the present invention provides apparatus for cooling a pressurised food process stream containing particulate material, the apparatus comprising an inner tube through which the process stream flows, an outer tube around the inner tube for carrying a cooling medium in heat exchange contact with the process stream, and means for injecting liquid into the process stream in the inner tube, the injected liquid being cooler than the process stream at the point of injection.

Preferably the liquid is injected into the process stream at or near the axial centre of the stream.

Preferably, the injected liquid forms part of the final product.

By injecting relatively cold liquid into the process stream, the cooling of the stream can be accelerated, and in particular it is possible to accelerate the cooling of the centre of the stream.

The cooling liquid is preferably injected via a nozzle which is adapted to promote mixing of the injected liquid with the process stream. The nozzle is preferably shaped to provide smooth flow of the stream around the nozzle, to reduce the likelihood of damage to the particulate material.

A second aspect of the invention provides a method of cooling a pressurised food process stream containing particulate material, the method comprising injecting into the stream a liquid which is cooler than the stream at the point of injection.

The degree of cooling obtained can be adjusted by varying the relative temperature of the injected liquid, the amount of the injected liquid and the point of injection along the stream flow.

Other preferred features and advantages of the invention will be apparent from the following description and the accompanying claims.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Fig. 1 illustrates a prior art system for cooling a process stream, with the associated temperature profile at the line X-X; Fig. 2 illustrates a system for cooling a process stream, forming an embodiment of the invention, with the associated temperature profile at the line Y-Y; Fig. 3 illustrates a system for cooling a process stream, forming a second embodiment of the invention, with the associated temperature profile at the line Z-Z; and Figs. 4a and 4b illustrate an end wall of a nozzle of the embodiment of Figs. 2 and 3.

Referring to Fig. 1, a prior art system for cooling a pressurised food process stream containing a particulate material, comprises a circular cross-section inner tube 2 in which the stream 4 is flowing in the direction of the arrow. An outer tube 6 surrounds the inner tube 2 and a cooling medium 8, such as water, flows in the space between the tubes 2, 6. Due to the generally lamina flow of the process stream, it can be seen that the temperature of the stream at the centre of the tube 2 will be higher than at the edges, thus increasing'the cooking value for the product travelling near the centre of the tube.

In Figs. 2 and 3 like parts have been given like reference minerals. Fig. 2 illustrates a first embodiment of the invention, in which a nozzle 12 is positioned on the axis of the tube 2. The nozzle is fed with a liquor 14 via a tube 16 which passes through the wall of the tube 2, the tube 6 being interrupted at this point. The liquor 14 is colder than the process stream in the region of the nozzle 12. The nozzle is of circular cross-section and has an end wall 18 with one or a plurality of apertures (see Fig. 4) to release the cold liquor into the centre of the stream 4. It can be seen that cooling will take place in the centre region, serving to equalise the temperature profile across the tube 2, and in particular enhance cooling in the axial region.

In the embodiment of the invention illustrated in Fig.

3, the nozzle 12 has axially extending slots 20 which release the liquor 14 in a radial direction to distribute the liquor further across the tube and provide some gentle turbulence to the flow of material and so further equalise the temperature profile across the tube 2. The end wall 18 of the nozzle may be apertured or blank. The slots 20 may extend helically about the axial direction, and may be zoned so that a first axial length of the nozzle has helical slots of one hand and a second axial length of the nozzle has helical slots of the other hand, etc.

As seen in Figs. 4a and 4b, the end wall 18 of the nozzle 12 may have one or a plurality of circular apertures 22, or a variety of other configurations may be used.

The nozzle 12 is preferably shaped to allow smooth flow of the stream past the nozzle, to reduce the risk of damage to the particulate material, turbulence being induced by the direction and velocity of the injected liquor 14, when desired.

Typically the tube 16 and nozzle 12 may be shaped similar to a conventional temperature probe.

The liquor preferably forms part of the final product, and so the flow volume of the liquor is adjusted accordingly. In turn, the temperature of the injected liquor, the relative flow volumes of the liquor and stream, and the point of injection along the stream can be selected to provide the desired degree of cooling.

Various modifications may be made to the described embodiments and it is desired to include all such modifications as fall within the scope of the invention described herein.

Claims

1. Apparatus for cooling a pressurised food process stream containing particulate material, the apparatus comprising an inner tube through which the process stream flows, an outer tube around the inner tube for carrying a cooling medium in heat exchange contact with the process stream, and means for injecting liquid into the process stream in the inner tube, the injected liquid being cooler than the process stream at the point of injection.

2. Apparatus as claimed in claim 1, wherein the means comprises a nozzle adapted to inject liquid into the process stream at or near the axial centre of the stream.

3. Apparatus as claimed in claim 2, wherein the nozzle has a wall at a downstream end and an aperture in the wall for the liquid to exit into the process stream.

4. Apparatus as claimed in claim 1 or 2, wherein the nozzle has a tubular wall extending in the direction of flow of the process stream, and an aperture in the wall for the liquid to exit into the stream.

5. Apparatus as claimed in claim 4, wherein the aperture in the tubular wall is an elongate slot.

6. Apparatus as claimed in claim 4, wherein the aperture in the wall is elongate and extends in a helical direction about the axial direction.

7. Apparatus for cooling a pressurised food process stream containing particulate material, substantially as hereinbefore described with reference to Fig. 2 or 3 of the accompanying drawings.

8. A method of cooling a pressurised food process stream containing particulate material, the method comprising injecting into the stream a liquid which is cooler than the stream at the point of injection.

9. A method as claimed in claim 8, wherein the injected liquid forms part of the final product.

10. A method as claimed in claim 8 or 9, wherein the liquid is injected into the centre of the process stream and a cooling jacket surrounds the stream.

11. A method of cooling a pressurised food process stream, substantially as hereinbefore described with reference to Fig. 2 or 3 of the accompanying drawings.