Method and apparatus for processing flowable food products

Abstract

An apparatus 3 for processing fluids (e.g. soup or flowable food) comprises a body through which extends a duct 6, 10 for flow of a primary fluid, the duct comprising an inlet at an upstream end of the duct and an outlet at a downstream end of the duct, a plenum chamber 12 disposed adjacent the duct configured to receive a secondary fluid (e.g. steam to heat or mix the flowable food), a first orifice 35a connecting the plenum chamber to the duct for the introduction of the secondary fluid into the duct; and a second orifice 35b connecting the plenum chamber 12 to the duct for the introduction of the secondary fluid into the duct downstream of the first orifice. An installation for processing a flowable food product comprising a vessel, a source of steam, a hollow lance or conduct and the apparatus for processing fluids.

Description

The present invention relates to a method and apparatus for the industrial processing of flowable food products and other fluids. It is known to inject steam into an industrial cooking vessel containing a flowable food product, such as soup or stew, in order to cook or partially cook the food product. Systems known for this purpose are disclosed in GB2452707A and GB 2490022A. The present invention seeks to provide an apparatus and method which may be used to process flowable food products more rapidly and effectively. Herein, "processing" a food product includes the heating and cooking thereof, as well as mixing. Although the invention will be disclosed in the context of industrial food processing (including using steam as a heat source), it may be employed in other industries, including the brewing, water treatment and petrochemical industries, for example, with or without heating, and as a fluid mover. The present invention provides an apparatus for processing fluids comprising: a body through which extends a duct for flow of a primary fluid, the duct comprising an inlet at an upstream end of the duct and an outlet at a downstream end of the duct; a plenum chamber disposed adjacent the duct and configured to receive a secondary fluid; a first orifice connecting the plenum chamber to the duct for the introduction of the secondary fluid into the duct; and a second orifice connecting the plenum chamber to the duct for the introduction of the secondary fluid into the duct, the second orifice being downstream of the first orifice. The apparatus may be configured to homogenously mix the primary fluid and the secondary fluid. The primary fluid may be a flowable food product, such as soup, stew, condiment, pie filling or the like. The secondary fluid may be steam, although other fluids such as air, liquid Nitrogen, etc. may be used depending on the type of processing required. The processing may comprise heating, cooling or mixing. Advantageously, by using two orifices for injection of the secondary fluid into the duct, mixing of the primary fluid and the secondary fluid can be enhanced. Furthermore, a greater quantity of secondary fluid can be injected into the primary fluid without causing the steam hammer effect than is possible via a single orifice. Thus, rapid processing of the primary fluid can be achieved without he need for multiple injection apparatuses. In use, the secondary fluid entering the duct through the orifices may cause the primary fluid to be drawn into the duct through the inlet and to be discharged through the outlet. This may be achieved by virtue of the Venturi effect. That is, the injected secondary fluid may be injected into the duct at a relatively high velocity, which causes a reduction in pressure within the duct on an upstream side of the orifice, which in turn draws the primary fluid into the duct. The duct may comprise an expansion chamber downstream of the second orifice. The expansion chamber may comprise a flared or frusto-conical portion of the duct. By expanding the mixed primary and secondary fluid, when the secondary fluid is steam, bubbles of steam may collapse such that the energy of the steam is effectively transferred to the primary fluid. The duct may comprise an upstream portion, which is upstream of the expansion chamber. The upstream portion may have a substantially constant cross-section shape, which may be circular. One or each of the first orifice and the second orifice may comprise a substantially continuous slot circumscribing the duct. However, in other embodiments, one or each of the first orifice and the second orifice may comprise one or more slots, holes or nozzles intermittently circumscribing the duct One or each of the first orifice and the second orifice may have a width of at least 0.1mm, or at least 0.2mm, or at least 0.5mm. One or each of the first orifice and the second orifice may have a width of less than 2mm, or less than 1.5mm, or less than 1mm. The first orifice may be wider than the second orifice. For example, the first orifice may have a width of about 0.5mm (e.g. between 0.4mm and 0.6mm) and the second orifice may have a width of about 1mm (e.g. between 0.8mm and 1.2mm). The width of an orifice should be understood to mean the maximum opening of the orifice in an axial direction of the duct. One or each of the first orifice and the second orifice may be configured to inject the secondary fluid into the duct at an angle of greater than 5°, or greater than 10° or greater than 15° with respect to an axial direction of the duct. One or each of the first orifice and the second orifice may be configured to inject the secondary fluid into the duct at an angle of less than 45°, or less than 30° or less than 25° with respect to an axial direction of the duct. The axial direction of the duct will typically by parallel to the wall of the duct in which the orifice is formed. In one example, each of the first orifice and the second orifice may be configured to inject the secondary fluid into the duct at an angle of about 20° (e.g. between 15° and 25°) with respect to an axial direction of the duct. An optimum angle exists for maximising suction of the primary fluid into the duct, whereby increasing or decreasing the angle of injection compared to this optimum angle will reduce the flow rate of the primary fluid. However, the specific angle depends on a number of factors, such as the particular fluids used as the primary and secondary fluids, and also the pressure of the secondary fluid. The angles given above have been found to be effective across a range of typical fluid types. One or each of the first orifice and the second orifice has a focal distance of between 0.5 times a diameter of the duct and 3 times the diameter of the duct, and optionally between 1 times a diameter of the duct and 2 times the diameter of the duct. The focal distance of the duct should be understood to mean the notional point or plane where the flow of secondary fluid from the orifice converges. The first orifice and the second orifice may be spaced at least 5mm, or at least 10mm apart in an axial direction of the duct. The apparatus may comprise no orifice connecting the duct and the plenum chamber between the first orifice and the second orifice. Theoretically, there is no maximum distance between the orifices. However, for ergonomic reasons, the first orifice and the second orifice may typically be spaced less than 10cm, or less than 5cm apart in an axial direction of the duct. The plenum may at least partially surround a section of the duct, and may optionally fully surround the section of the duct. That is, the plenum may be approximately a cylindrical annulus. The section of the duct may be upstream of the expansion chamber. The section of the duct may be adjacent the first orifice and the second orifice. The plenum may be configured to connect to a conduct for communicating with a source of the secondary fluid. The connection for the conduit may be axially downstream of the second orifice. The plenum may be configured to impart spin to the secondary fluid. For example the plenum may comprise fins or rifling. This arrangement may cause the secondary fluid to enter the duct with angular momentum. The apparatus may further comprise an insulation chamber disposed radially outwards of the plenum chamber. The insulation chamber may comprise insulation material, such as a ceramic fibre or Rockwool. In other embodiments, the insulation chamber may comprise a gas, such as air, and / or at least a partial vacuum, i.e. having a pressure below 0.5 bar. When the process includes heating or cooling, a significant temperature differential will occur between the plenum holding the hot or cold secondary fluid and the primary fluid outside of the apparatus. Where the primary fluid outside of the apparatus is not moving, or moves only slowly past the apparatus, it could be scalded or frozen. Providing an insulation chamber radially outwards of the plenum chamber reduces this risk. The apparatus may be so dimensioned that, in use when the secondary fluid is steam, substantially all of the steam entering the apparatus collapses into water before reaching the outlet. This may be assisted by the expansion chamber of the duct. The apparatus may comprise only a single body and a single duct extending therethrough. The body of the apparatus may be made from a food-safe material, and preferably a food-safe metal material, such as stainless steel. An external surface of the body of the apparatus may be polished. Such materials do not contaminate food products, and may be effectively cleaned or even sterilised between batches of product. The body may be formed from a plurality of body components. One or more body components may be joined by friction-fit or by threaded connections. Thus, the relative positions of the body components may be adjustable, for example to modify a size of the first orifice and / or second orifice. One or more or all of the body components may be permanently joined, for example by welding. Thus, the apparatus cannot be disassembled or adjusted after manufacture. Viewed from a second aspect, the present invention also provides an installation for processing a flowable food product, the installation comprising: a vessel for containing the flowable food product; a source of steam; a hollow lance or conduct for communicating with said source of steam; an apparatus according to any preceding claim coupled to the lance or conduit. The apparatus may be configured to cause circulation of the primary fluid within the vessel. The apparatus may be detachably coupled to the lance or conduit, for example by a threaded connection, a bayonet connection, a friction-fit connection or other suitable connection permitting non-destructive disconnection of the apparatus from the lance or conduit. The lance or conduit or may be configured to be movable between an first position within the vessel and a second position external to the vessel. This may permit additions to be made to the primary fluid (e.g. addition of ingredients) or cleaning of the vessel. An embodiment of the invention will now be described in greater detail by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic illustration of an apparatus for heating and mixing a flowable food product within a cooking vessel; Figure 2 is an end view of the apparatus; Figure 3 is an axial section through the apparatus taken on the line ll-ll in Figure 2; Figure 4 is an exploded axial section through a first outer body component, a second outer body component, and an inner body component of the apparatus; and Figure 5 is an axial section through a third outer body component of the apparatus. Referring to Figure 1, a vessel A in the form of an industrial cooking kettle contains a quantity of a flowable food product B such as soup or stew, which constitutes a primary fluid. A tubular lance or conduit 4 is connected to a source of steam S which is used as a secondary fluid to cook, or at least to heat, the food product B, and promote its circulation within the vessel A. An apparatus 2 incorporates one or more steam injectors 3 and is screwed onto or otherwise removably mounted on the end of the lance or conduit 4, such as to serve as a detachable nozzle. The lance or conduit 4 may be a fixture within the vessel A or movable from a rest position externally of the vessel A into an operational position within the vessel A. In a first embodiment, the apparatus 2 incorporates a single steam injector 3. A substantially unobstructed duct (not shown in Figure 1) extends from an inlet of the steam injector 3 (on the left-hand side as viewed in Figure 1) to an outlet of the steam injector 3 (at the right-hand side as viewed in Figure 1). Steam S fed to the steam injector 3 through the lance or conduit 4 is injected into the duct and draws food product B into the duct through the inlet as indicated by arrows C and discharges it through the outlet as indicated by arrows D. The food product B is heated as it passes through the duct. In industrial fields other than food processing, or when only mixing (and not heating) of the contents of a vessel A is required, a secondary fluid other than steam S may be employed, such as air or liquid Nitrogen. Thus, hot or cold gases, vapours or fluids other than steam may be used to promote the circulation or mixing of a primary fluid B. Also, the apparatus 2 may be used to mix the primary fluid B and the secondary fluid S together. In the case of a second embodiment (not shown), the apparatus 2 may incorporate two or more steam injectors 3 arranged side by side in parallel. Generally the apparatus 2 is arranged in such a way that the food product B is mixed homogenously with the steam S. It is desirable to prevent the external surfaces of the steam injector or injectors 3 becoming heated because this could lead to food product B in the vessel A being scalded. Prevention of such scalding may be achieved by positioning of thermal insulation chambers 16 within the body or bodies of the steam injector or injectors 3. The construction and operation of embodiments of the apparatus 2 will now be described in greater detail, by way of example. A first embodiment of the apparatus 2 consists of a single steam injector 3, as shown in Figures 2 to 4, for injecting or introducing steam S into a flowable food product B, such as soup or stew. The injection, discharge or introduction of steam S into the food product B takes place wholly within the steam injector 3. The steam injector 3 has a body of substantially circular cross-section machined from stainless steel, the external surfaces of the body being polished. An elongate, rectilinear duct, of circular cross-section, extends through the body and has an upstream section indicated at 6, and a downstream section indicated at 10. The duct is unobstructed throughout its entire length. An inlet at the upstream end of the duct is surrounded by an inlet rim 8 and an outlet at the downstream end of the duct is surrounded by an outlet rim 9. The upstream section 6 of the duct is delimited by the substantially cylindrical radially inner surfaces of a pair of peripheral walls 24a, 24b and a substantially cylindrical portion of the inlet rim 8, such surfaces being of circular cross-section and of substantially constant diameter throughout the length of the upstream section 6 of the duct. The peripheral walls 24a, 24b separate the upstream section 6 of the duct from an annular plenum chamber 12 which surrounds the duct. Within the scope of the invention the radially inner surfaces may depart from a true cylindrical shape, provided that this does not interfere with operation of the apparatus 2. The downstream section 10 of the duct is delimited by the radially inner surface of a peripheral wall 7 of flared or frusto-conical shape. The flared or frusto-conical shape helps to collapse the steam bubbles. Throughout its length, the inner surface of downstream section wall 7 has a diameter which, at least on average, is greater than the internal diameter of the peripheral walls 24a, 24b. As a result, the cross-sectional area of the downstream section 10 of the duct is, on average, greater than the cross-sectional area of the upstream section 6 of the duct. A steam inlet passage 14 extends radially through the body of the steam injector 3 to open into the plenum chamber 12, and a pair of constricted annular orifices 35a, 35b open from the plenum chamber 12 into the upstream section 6 of the duct, as will be described in greater detail below. Disposed within the body, radially outwardly of the plenum chamber 12, is a closed, annular chamber 16 bounded on its radially outer side by a cylindrical cladding ring 18 (not shown in Figure 2) manufactured from thin sheet stainless steel. The edges of the cladding ring 18 are received in rebates 17 in the edges of the chamber 16, and held in place by welding or other suitable means. The outer surface of the cladding ring 18 is polished so as to appear indistinguishable from the body of the steam injector 3. The steam inlet passage 14 passes through the annular chamber 16 and opens into the plenum chamber 12. The chamber 16 serves to provide thermal insulation as explained below. The plenum chamber 12 is bounded on its radially inner side by the radially outer surfaces of the peripheral walls 24a, 24b. On its radially outer side the plenum chamber 12 is bounded by outer walls 28, 29 of the steam injector 3 (save where these are penetrated by the inlet 14 where it opens to the plenum chamber 12). At its upstream end the plenum chamber 12 is bounded by an annular surface or wall 25 machined into the inlet rim 8. At its downstream end the plenum chamber 12 is bounded by an annular surface or wall 58. Optionally, the plenum chamber 12 may include fins or rifling configured to impart spin to the steam S flowing through the plenum chamber 12, such that it enters the upstream section 6 of the duct with angular momentum. The body of the steam injector 3 is assembled from a plurality of body components 50 to 53, shown in Figures 5 and 6. Figure 5 depicts a first outer body components 50, a second outer body component 51, and an inner body component 53. Surfaces of the first and second outer body components 50, 51 are associated with the first (upstream) orifice 35a. Surfaces of the second outer body component 52 and the inner body component 53 are associated with the second (downstream) orifice 35b. The first outer body component 50 comprises the inlet rim 8. As described above, an annular wall or surface 25 is recessed into the inlet rim 8. The wall or surface 25 is substantially radial. A radially inner edge of the wall or surface 25, located on the downstream side of the inlet rim 8, has a frusto-conical surface portion 26 inclined in the downstream direction. The surface portion 26 terminates where it meets the cylindrical portion 8A on the interior of the inlet rim 8 enclosing the upstream duct section 6. The second outer body component 51 comprises the outer wall 28 of the body and the first (upstream) peripheral wall 24a. The first peripheral wall 24a is supported by braces, ribs or the like (not shown) coaxially with respect to the outer wall 28. The first peripheral wall 24a is of a substantially constant thickness and diameter, except at its upstream and downstream ends. At its upstream end, the first peripheral wall 24a has a frusto-conical surface portion 33, which is substantially parallel to the outwardly facing annular surface 27. An annular passageway of substantially constant width throughout its extent is defined between the frusto-conical surface portion 26 of the inlet rim 8 and the frusto-conical surface portion 33 on the upstream end of the first peripheral wall 24a. The passageway leads from the end of the plenum chamber 12 and terminates at the first orifice 35a, which opens into the upstream section 6 of the duct, immediately to the rear of the inlet rim 8. It will be understood that the upstream orifice 35a need not completely encircle the axis CL of the duct but may be interrupted at intervals. For example, the upstream orifice 35a may comprise one or more slots, holes or nozzles coupling the plenum chamber 12 to the duct. At its downstream end, the first peripheral wall 24a has a frusto-conical surface portion 34 inclined in the downstream direction. The frusto-conical surface portion 34 terminates where it meets the inner cylindrical surface of the first peripheral wall 24a enclosing the upstream duct section 6. The inner body component 53 includes the second (downstream) peripheral wall 24b. The second peripheral wall 24b has a substantially constant inner diameter. The thickness of the second peripheral wall 24b varies along its length. At the axial position corresponding to the steam injection passage 14, the second peripheral wall 24b is thinner to enlarge the plenum 12 at this axial position. At an upstream end, the second peripheral wall 24a has a frusto-conical surface portion 36, which is substantially parallel to the outwardly facing annular surface 34 of the first peripheral wall 24b. An annular passageway of substantially constant width throughout its extent is defined between the frusto-conical surface portion 34 on the downstream end of the first peripheral wall 24a and the frusto-conical surface portion 36 on the upstream end of the second peripheral wall 24a. The passageway leads from the end of the plenum chamber 12 and terminates at the downstream orifice 35b, which opens into the upstream section 6 of the duct. It will be understood that the downstream orifice 35b need not completely encircle the axis CL of the duct but may be interrupted at intervals. For example, the downstream orifice 35b may comprise one or more slots, holes or nozzles coupling the plenum chamber 12 to the duct. The inner body component 53 has a relatively large diameter base portion 54 from which projects the second peripheral wall 24b in the form of a tubular extension. The base portion 54 of the inner body component 53 is formed on its inner side with the outwardly flared or frusto-conical widened surface 7 which serves as an expansion chamber for the downstream section 10 of the duct. The inlet rim 8, and the surface or wall 25 which delimits the plenum chamber 12 at its upstream end are provided or formed on the first outer body component 50, whereas the downstream end wall of the plenum chamber 12 is formed in part by the wall or surface 58 which takes the form of a step between the larger diameter base portion 53 and the second peripheral wall 24b of the inner body component 53. Turning now to Figure 6, the third outer body component 52 comprises the second outer wall 29, which is substantially cylindrical. The third outer body component 52 is formed at its downstream end with an end piece 68. The periphery of the third outer body component 52 is cut away at 60 so as to form an annular recess, which is rebated along its edges at 17, and serves as the radially inner region of the chamber 16. The third outer body component 52 is provided with a friction-fit surface 54A on the end piece 68 and the inner body component 53 is provided with a complementary friction-fit surface 54B. The third outer body component 52 is also provided with a friction-fit surface 55A on the upstream edge of the outer wall 29 and the second outer body component 51 is provided with a complementary friction-fit surface 55B on the downstream edge of the outer wall 28. The second outer body component 51 is also provided with a friction-fit surface 56A on the upstream edge of the outer wall 28 and the first outer body component 50 is provided with a complementary friction-fit surface 56B on the downstream edge of the rim 8. Whilst friction-fit surfaces are illustrated, in other embodiments the components 50-53 of the steam injector 3 may be connected in other ways, such as using threaded engagement or the like. After the respective body components 50-53 of the steam injector 3 are assembled to the desired configuration, they may be welded together to prevent movement of the components 50-52 during operation and / or disassembly of the steam injector 3 The steam injector 3 is assembled by connecting the first, second and third outer body components 50, 51, 52 together, and screwing them into place to form a combined outer body component. Then, the inner body component 53 is introduced into the combined outer body component and screwed it into place. The cladding ring 18 is introduced into the rebates 17 and welded or otherwise secured in place. The apparatus 2 may then be screwed onto a lance or conduit 4. In operation, steam S is supplied through a lance or conduit 4 to steam inlet 14 and flows into the plenum chamber 12. It escapes into the passageway leading to the orifices 35a, 35b, and is then injected at high velocity into the upstream duct section 6 via the orifices 35a, 35b. The steam S then flows in the downstream direction towards the outlet of the steam injector 3. The orifices 35a, 35b are oriented to inject steam S at an angle with respect to the central axial direction of the duct. Food product B is thereby drawn into the inlet of the duct and passes through the inlet and along the duct, being heated and mixed with the steam S, and ultimately discharged from outlet. Thus, the orifices 35a, 35b cause the steam injector 3 to act as a Venturi ejector. A reduction in pressure takes place in the downstream section 10 of the duct. On being discharged from the apparatus the food product circulates within the kettle A. The steam S expands and collapses, or is condensed, into water within the expansion chamber formed by the downstream section 10 of the duct, the frusto-conical or flared shape of which ensures that the size of any remaining globules of steam S is controlled, and that substantially all of the energy contained in the steam is imparted to the food product B. In the ideal case, all such steam S entering the expansion chamber 10 collapses into water, with the result that only water and food product B are discharged from the outlet. The optimum shape of an expansion chamber 10 may therefore be such as to lead to expansion and collapse of the steam S into water, and to be capable of imparting substantially all of the energy remaining in the steam S to the food product B. The shape and dimensions of the optimum expansion chamber 10 may be determined by experiment. If the downstream end of the duct were to have the same internal cross-sectional diameter as the peripheral walls 24a, 24b, turbulence could occur, and globules of steam S escape from the steam injector 3 and rise to the surface of the food product B in the kettle A, without the energy in the steam S being substantially fully imparted to the food product B. It will be noted that the radially inner surface of the upstream end of the expansion chamber 10 adjoins, substantially, the downstream end of the radially inner surface of the second peripheral wall 24b, which is of constant inner diameter throughout its length. The chamber 16 serves to thermally insulate the food product B relative to hottest zones within steam injector 3, and may contain air, a vacuum or partial vacuum, or an insulating material such as a ceramic fibre or Rockwool (Trade Mark). The optimum width of the orifices 35a, 35b, may be determined by experiment. Adjusting the widths of the orifices 35a, 35b can result in different mixing characteristics, for example increasing the gap size may result in steam collapsing in larger quantities, and a more vigorous agitation, which could benefit the mixing process in some circumstances. Setting the optimum gaps results in the ideal optimised flow of steam S through the steam injector 3, which transfers substantially all of its energy into the food product B. This suppresses the noise of the steam S (steam hammer as it is termed), which results from steam collapsing into water. Hot gases or vapours, other than steam S, may be used in certain alternative circumstances. Advantageously, the upstream orifice 35a has a larger width than the downstream orifice 35b. In the illustrated example, the upstream orifice 35a has a width of approximated 1.0 mm, for example between 1.2 mm and 0.8 mm, and the downstream orifice 35b has a width of approximately 0.5 mm, for example between 0.6 mm and 0.4 mm. The optimum angles of the orifices 35a, 35b, may be determined by experiment. Adjusting the angles of the orifices 35a, 35b can result in different mixing characteristics within the steam injector 3. In the illustrated example, both orifices 35a, 35b have the steam injection angle of approximately 20°, for example between 15° and 25°. This angle has been found optimal to maximise the rate at which the food product B is drawn through the steam injector 3. However, within the scope of the invention, the orifices 35a, 35b may have different steam injection angles. The use of two orifices 35a, 35b enhances mixing of the steam S and the food product B within the steam injector 3, and permits injection of a greater quantity of steam S using a single steam injector 3 without causing the steam hammer effect than is possible via a single orifice. The preferred angle at which the expansion chamber 10 is flared may also be determined by experiment. Although it is preferred for the outlet to open directly from the expansion chamber 10, a steam injector 3 in which there is a duct portion of constant diameter between the frusto-conical wall 7 of the expansion chamber 10 and the outlet rim 9 is also intended to fall within the scope of the invention. For convenience of manufacture, the expansion chamber 10 is circular in cross-section, although it is to be understood that expansion chambers 10 of other cross-sectional shapes (for example, square or elliptical cross-sections) are intended to fall within the scope of the invention. Within the scope of the invention the expansion chamber 10 may be 5 cylindrical in shape (not shown), although performance will be less controlled than with a flared or frusto-conical expansion chamber 10. Advantages of the invention are that the food product is heated very rapidly with substantially 100% efficiency. Apparatus or steam injectors as described and illustrated may be used for reducing starches and as an entrainment system for 10 starches and similar substances. The expansion and collapse of steam which takes place in the expansion chamber gives a much-improved activation. Far less starch is needed to obtain the same thickening results.

Claims

1. An apparatus for processing fluids comprising:a body through which extends a duct for flow of a primary fluid, the duct comprising an inlet at an upstream end of the duct and an outlet at a downstream end of the duct;a plenum chamber disposed adjacent the duct and configured to receive a secondary fluid;a first orifice connecting the plenum chamber to the duct for the introduction of the secondary fluid into the duct; anda second orifice connecting the plenum chamber to the duct for the introduction of the secondary fluid into the duct, the second orifice being downstream of the first orifice.

2. An apparatus according to claim 1, wherein, in use, the secondary fluid entering the duct through the orifices causes the primary fluid to be drawn into the duct through the inlet and to be discharged through the outlet3. An apparatus according to claim 1 or 2, wherein the duct comprises an expansion chamber downstream of the second orifice.

4. An apparatus according to claim 3, wherein the expansion chamber comprises a flared or frusto-conical portion of the duct.

5. An apparatus according to any preceding claim, wherein each of the first orifice and the second orifice has a width of between 0.1mm and 2mm.

6. An apparatus according to any preceding claim, wherein the first orifice is wider than the second orifice.

7. An apparatus according to any preceding claim, wherein each of the first orifice and the second orifice is configured to inject the secondary fluid into the duct at an angle of between 10° and 30° with respect to an axial direction of the duct.

8. An apparatus according to any preceding claim, wherein each of the first orifice and the second orifice has a focal distance of between 0.5 times a diameterof the duct and 3 times the diameter of the duct9. An apparatus according to any preceding claim, wherein the first orifice and the second orifice are spaced at least 10mm apart in an axial direction of the duct.

10. An apparatus according to any preceding claim, wherein the plenum surrounds a section of the duct.

11. An apparatus according to any preceding claim, further comprising: a chamber containing thermal insulation disposed radially outwards of the plenum chamber.

12. An apparatus according to any preceding claim, wherein the apparatus is so dimensioned that, in use when the secondary fluid is steam, substantially all of the steam entering the apparatus collapses into water before reaching the outlet.

13. An apparatus according to any preceding claim, wherein the apparatus comprises a single body and a single duct extending therethrough.

14. An installation for processing a flowable food product, the installation comprising:a vessel for containing the flowable food product;a source of steam;a hollow lance or conduct for communicating with said source of steam;an apparatus according to any preceding claim coupled to the lance or conduit.16

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