GB2265545A - Apparatus for preparation of a food product - Google Patents

Abstract

Apparatus for preparation of a food product having a cooked upper surface, comprises a heat source (22), a conveyor for containers for products to be subjected to heat from the heat source (23), means for directing a source of cooling fluid (25) such as compressed air onto portions of the containers (21) while they move along the conveyor. The means for directing the cooling fluid onto the containers may be ducts, which direct the containers in their movement along the conveyor. <IMAGE>

Description

APPARATUS FOR PREPARATION OF A FOOD PRODUCT This invention relates to apparatus for preparation of a food product and a method of producing a food product with a cooked upper surface, particularly though not exclusively, a food product to be re-heated or cooked in a microwave oven.

For some time, manufacturers have provided prepared convenience meals or food products for consumption at home which are cooked or re-heated in microwave ovens. Such meals, which may be supplied uncooked, partially cooked or completely cooked, are re-heated in a microwave oven. There has been an increasing demand for these types of food product. However, it is not possible to cook the surface of food in a microwave oven to make the surface brown or crisp or both, which would have surface characteristics such as might result from cooking in a conventional oven. Instead, the products appear white or pale and have a soft and soggy surface after cooking, due to the microwave energy driving moisture from the centre of the product to the surface.The crisp texture of the surface of cooked food products such as pies with pastry or potato toppings, pasta products and baked foods, is an important feature of the food being consumed. Food products cooked or reheated in a microwave oven have an uncooked appearance and the result is a meal which is less appealing to the consumer.

One solution to this problem is to cook the food product in the microwave oven and then brown and crisp the surface using a conventional oven. However, this increases the preparation time and reduces the convenience of the prepared food product defeating the object of such meals. Furthermore, food products to be heated in a microwave oven must be held or packaged in a non-metallic container; these are generally composed from plastic or board type materials which have a tendency to burn, melt or distort at the temperatures required in a conventional oven for browning or crisping the surface.

Manufacturers of microwave ovens have attempted to overcome the problem by incorporating an infra-red heating element in the domestic microwave oven to provide energy of the appropriate wavelength to cook the surface of the food product to make it brown and crisp. However, these ovens are more expensive to manufacture, and therefore have a higher purchase price and are much less widespread than conventional microwave ovens. The majority of people owning microwave ovens still experience problems browning or crisping the surface of some prepared food products.

Alternatively, manufacturers of prepared food products may package the food in a container which is fitted with a metallised susceptor, essentially a metallised sandwich film which converts microwave energy into conventional heat, which browns and crisps the surface of the food product in contact with it. However, the surface browning obtained tends to appear mottled or burnt and the process is somewhat variable making the manufacture of prepared quality food products which will brown consistently a difficult task.

Another solution to the problem of producing a food product with a brown or crisp surface involves providing a mixture of amino acids and sugars to the pastry or to spray such a mixture onto the surface. The low temperature of the microwave oven triggers a browning reaction which colours the surface. The results of this technique are inconsistent and generally unacceptable.

An alternative approach to the production of a cooked food product with a brown or crisp surface after cooking in a microwave oven, is to cook the surface of a food product to make it brown or crisp or both prior to it being sold.

However, a number of problems must be overcome before this can be achieved, in particular, the problem of heating a food product in a product container which is capable of withstanding the temperatures required in a conventional oven for browning, but which is also unaffected subsequently when the food product is exposed to microwave radiation. Suitable containers unaffected by exposure to microwave radiation may be constructed from polyethylene terephthalate (PET), but these containers are prone to distort or melt at temperatures necessary to cook the surface of a prepared food product to make it brown or crisp.

The present invention provides a technique for preparing a cooked surface, which makes use of cooling fluid directed onto the walls or other exposed surfaces of a container for the product.

In one aspect, the invention provides apparatus for preparation of a food product having a cooked upper surface, which comprises: (a) a heat source; (b) a conveyor for containers for products to be subjected to heat from the heat source; (c) means for directing a source of cooling fluid onto portions of the containers while they move along the conveyor.

The apparatus of the invention has the advantage that the surface of a food product can be cooked to make it brown or crisp or both in a continuous process without melting or distorting the microwave-safe food containers. Preferably, the heat source is a radiative heat source. A suitable radiative heat source may be any one of a number of units presently available for use in the food industry, for example infra-red radiators with highly polished reflectors. The conveyor, possibly of a stainless steel metal mesh construction, moves food containers and the food product under the radiative heat source. Cooling fluid is applied to the exposed surfaces of the food containers during and, if necessary, after the cooking step, to prevent the containers from melting or distorting.

This is especially important if a lid or sealing film is to be applied to the finished product. A distorted food container may result in a failed seal and the product would have to be rejected.

Air would be a suitable cooling fluid though it must be understood that any cooling medium which prevents the food container from melting would also be effective.

The cooling fluid directing means may comprise at least one duct having apertures in its wall through which the cooling fluid can pass out of the duct onto containers on the conveyor.

By providing apertures in the wall of the duct it is possible to cool an area uniformly by accurately directing cooling fluid onto regions of the container which may be affected by the heat. The exact shape of the duct cross-section is not critical to the operation of the invention as long as it can deliver sufficient cooling fluid to the walls of the containers. The duct may have the form of a pipe or tube of circular or rectangular cross-section.

Preferably, the apparatus includes at least two ducts, one duct being provided along each side of the conveyor. This further enhances the efficiency of the cooling of the container walls.

At least one duct can be positioned alongside the conveyor, so as to guide the containers as they move along the conveyor, the cooling fluid being directed onto the side walls of the containers. This avoids the need to use separate guiding and cooling means and provides a compact system. With this configuration of guiding and cooling means, the flow of cooling air directed from the ducts will not be interrupted. It can be particularly advantageous to direct the cooling fluid onto the lips of the container walls at the open upper face of the container.

Conveniently, a plurality of ducts define a plurality of channels along which food containers may be moved by the conveyor. This has the advantage that more than one channel or product lane may be created on the same conveyor and therefore has the advantage that the surfaces of more than one food product may be cooked side by side with walls of adjacent food containers being cooled from one duct. For a given conveyor speed, the quantity of food product being processed can be substantially increased making the overall operation more economical.

When more than one duct is provided for the supply of cooling fluid, individual ducts can carry cooling fluid to the containers on the conveyor, or carry cooling fluid from the containers on the conveyor. For example, when there are two ducts, one duct will be provided for the supply of cooling fluid. The other duct may also be used for the supply of cooling fluid, or it may remove cooling fluid supplied by means of the first duct.

Fastening means may be provided on the ducts so that the channels, defined by the ducts, may be adjusted to accommodate a plurality of food container sizes. A particular prepared food product or specified quantity of food may be packaged in a certain size or shape of food container. By having adjustable ducts it is possible to cook the surface of the food present in different sized containers, for example, a prepared food product may be for one or two persons and may, accordingly, be manufactured in different size containers.

The apparatus may include means for supplying the cooling fluid to the at least one duct under pressure. Control of the cooling fluid pressure allows the system to cool the walls of food containers for different operating conditions. This would be necessary, for example, if the temperature of the heater modules were adjusted or changed or if the speed of the conveyor was altered, and therefore the time the food container and product were exposed to the operating temperatures.

Apertures may be provided on the upper wall of the ducts and which includes a deflector positioned above the apertures of the upper duct wall to deflect cooling fluid onto the containers. A deflector may be positioned above apertures in the upper duct wall so that cooling fluid discharged from apertures in the upper duct wall is deflected onto the food container, for example onto the upper edge or lip of the container. These portions of the food container are nearest to the heat source and can therefore be the parts of the container which are most susceptible to heat damage such as melting or distortion, although it should be noted that some softening of the container material is permissible since it can facilitate the application of a sealing plastic film to the upper edge or lip of the container.The deflector directs extra cooling fluid onto those areas of the food container where it is most needed. It is important to maintain the shape and condition of the lip or upper edges of the food container as a lid or plastic film may be applied to the container to seal it later on in the production line. The deflector may be connected to the duct by clips or other fastening means so that it may be removed, for example, during routine cleaning or maintenance.

Preferably, the apertures in the ducts are slots. A configuration of slots are more likely to prevent the development of hot spots or regions on the container surfaces than, for instance, an arrangement of circular apertures.

In a portion or length of duct, the drop in pressure in the cooling fluid which may occur as the result of a pressure gradient present along the duct may cause a sufficient reduction in volume of cooling fluid reaching the containers.

To help eliminate this effect the size of apertures at the high pressure end may be reduced and those at the low pressure end increased so that uniform flow rates are maintained throughout the apparatus.

The duct, or at least one of the ducts when more than one duct is provided, may comprise a plurality of independent duct sections. Each section may be independently supplied with cooling fluid which is discharged through the apertures in the duct walls. This is another method of reducing the effects of pressure gradients on the flow of cooling fluid and has the added advantage that cooling conditions in zones within the apparatus, and defined by the independent duct sections, may be independently controlled.

The apparatus may include means for extracting cooling fluid which has been directed onto portions of the containers while they move along the conveyor. This serves to reduce turbulence created over the surface of the food product by opposite air flows from adjacent ducts, which can reduce the efficiency of the process. By extracting through one duct and discharging through another it is possible to create laminar fluid flow over the food product which is less disruptive to the cooking process and improves efficiency.

Preferably, the cooling fluid extracting means comprises at least one duct having apertures in its wall through which the cooling fluid can pass into the duct. Uniform fluid flow characteristics may be obtained with this configuration.

The heat source may emit electromagnetic radiation having a wavelength which is greater than about 1 ym, for example in the range 2 to 4 ssm. An example of a wavelength of electromagnetic radiation for use with this apparatus would be about 3 ttm.

The apparatus may further include means for providing a lid on to the container, downstream along the conveyor of the heat source. It is desirable to have some form of lid or seal applied to the container before it leaves the factory. The food product has a longer shelf life and it is less likely that the food will be contaminated or tainted during transportation to consumer outlets.

In a further aspect, the invention provides a method of producing a food product with a cooked upper surface, which comprises: (a) placing the food product in a container on a conveyor; (b) moving the food product on the conveyor past a heat source; and (c) exposing portions of the container to a cooling fluid while it moves along the conveyor.

A plurality of food products, in respective containers, are moved on the conveyor past the heat source side-by-side. In this manner quantities of prepared food products may be cooked in a continuous manufacturing process.

Preferably, the portions of the container or containers which are exposed to the cooling fluid comprise side wall portions.

The lip and side wall portions are the external surfaces of the food container which are most susceptible to heat damage such as melting and distortion and must therefore be cooled with appropriate volumes of cooling fluid.

The conveyor may be provided with means for guiding the container or containers along it, and which includes the step of using the guide means to guide the container or containers along the conveyor. The guiding means maintain the orientation of the food container and prevent the containers moving laterally.

The guide means may comprise hollow ducts with apertures in their side walls, and which includes the step of supplying the cooling fluid to the container or containers through the ducts and the said apertures. A guiding means from which cooling fluid may be supplied results in a compact and efficient arrangement.

The material of the container or containers may be a polymeric material. Containers for food products which are to be cooked or re-heated in a microwave oven must be constructed from non metallic materials. Containers produced in polymeric materials, such as polyethylene terephthalate, can be easily formed in different shapes and sizes and are generally not affected by microwave radiation.

The surface of the food product may be heated to at least about 180 C, preferably at least about 200"C, for example about 210"C.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram showing the invention incorporated in a food production line; Figure 2 is a cross-sectional view transverse to the axis of the conveyor; Figure 3 is a perspective view of two possible configurations of cooling ducts; Figure 4 is a cross-sectional view of a food container and the flow of cooling air over the container according to one aspect of the invention; and Figure 5 is a cross-sectional view of a food container and the flow of cooling air over the container according to another aspect of the invention.

Referring to the drawings, Figure 1 shows two browning ovens 1 which accept food containers from the diverging conveyors 2, which increase the number of product lanes, for example, from three to six. The food containers move through the oven apparatus on a conveyor in the direction of the arrows 5 and out onto a feed conveyor 3 which carries the cooked food products to the spiral cooler 4. A lid or plastic film is applied to the container prior to supply to consumer outlets.

Figure 2 shows a cross-sectional view of the apparatus of the invention in greater detail. A food product 20 to be browned and crisped in a food container 21 is moved under heating modules 22 by a conveyor 23 along product lanes or channels 24 defined by cooling ducts 25, which function as guides for the containers. Cooling air is discharged, under pressure, through apertures present in the cooling ducts 25, in the direction of the arrows 26, and onto the side walls of the food containers 21 thereby keeping the walls of the containers cool. This prevents the food containers from heat damage such as melting or distortion, though softening of the container material is acceptable as this aids the application of a sealing plastic film. Heated air may be extracted through the side vents 28, along the sides of the conveyor.

The food containers are generally of a one piece moulded construction formed from a polymeric material, such as polyethylene terephthalate (PET), with upper edges or lips 27 formed on the upper edges of the side walls. The upper edges or lips are designed to accept a lid or to which a sealed plastic film may be applied once the food has been browned and crisped.

This maintains the freshness of the food within the container and promotes the shelf life of the product.

The cooling ducts 25 act as guides so that the conveyor moves the food containers down the product lanes 24. Cooling air is discharged from the cooling ducts via apertures in the walls of the ducts. These apertures or perforations may be holes or slots in a regular array or arrangement to provide a continuous flow of cooling air. The cooling ducts 25 may be arranged in sections with each section~independently supplied with cooling air. This allows cooling rates in zones within the oven to be accurately controlled and helps to reduce variations in cooling rates due to pressure gradients within the ducts. Different sizes of apertures may also be used to eliminate the effect of pressure gradients on cooling fluid flow rates on a given length of cooling duct.

The cooling ducts shown in Figure 2 have a circular crosssection, however, the cooling ducts may have a rectangular cross-section similar to those shown in Figure 3.

Figure 3 shows two possible configuration of cooling duct having a rectangular cross-section 30 and a plurality of inclined slots 31, spaced at regular intervals along the side walls 32 of the duct. Cooling air discharged from these slots cools the external, exposed side walls of the food container and prevents heat damage. Figure 3b shows a configuration of cooling duct which only provides cooling of the side walls of the food container through a regular arrangement of apertures.

Figure 3a shows a cooling duct with regularly spaced apertures 31 along the side walls 32 and a plurality of regularly spaced apertures 33 on the upper duct wall or face 34 with a deflector 35 connected to the cooling duct above the apertures on the upper face. Air discharged from the apertures in the upper face is deflected downwards, by the deflector, and onto the upper edge or lip of the food container. The lip or upper edges of the food containers are closest to the heating modules and are exposed to higher temperatures than other parts of the food container. These portions of the food container are therefore more susceptible to heat damage and it is desirable to be able to provide these parts of the container with additional cooling.The deflector may be connected to the cooling duct by clips or other known fastening methods which may allow the deflector to be removed for routine cleaning or maintenance. Arrows 36 show flow of cooling air within the ducts and discharged through the side wall apertures 31 indicated by the arrows 37. Figure 3a shows cooling air also discharged through the apertures 33 in the upper wall 34 of the cooling duct and deflected downwards by the deflector 35 in the direction of the arrow 38 onto the upper edge or lip of a food container.

Figure 4 shows a food container 40, formed from a plastics material such as PET, moved by a conveyor 41 and guided by two cooling ducts 42 and 43. Cooling air discharged through apertures in the walls of one cooling duct 43 passes onto and over the food container and is extracted through another cooling duct 42. The flow of the cooling air over the food container prevents the upper extremities of the container, such as the lip 44, from melting or distorting. This is important especially if a lid or sealed plastic film is to be applied to the food container. Said flow of air is essentially laminar and has a less disruptive effect on the browning process because there is substantially less turbulence created with this configuration than with opposite air flow from adjacent ducts. Air flow over the food container is indicated by the arrows 45, 46 and 47.

Figure 5 shows a food container 50, formed from a plastics material such as PET, moved by a conveyor 51 and guided by two cooling ducts 52, 53. Cooling air discharged through apertures in the walls of the cooling ducts 52, 53 passes onto and over the food container and is directed downwardly onto the container 50 and onto the surface of food in the container.

Claims (22)

CLAIMS:

1. Apparatus for preparation of a food product having a cooked upper surface, which comprises: (a) a heat source; (b) a conveyor for containers for products to be subjected to heat from the heat source; (c) means for directing a source of cooling fluid onto portions of the containers while they move along the conveyor.

2. Apparatus as claimed in claim 1, in which the cooling fluid directing means comprises at least one duct having apertures in its wall through which the cooling fluid can pass out of the duct onto containers on the conveyor.

3. Apparatus as claimed in claim 2, which includes at least two ducts, one duct being provided along each side of the conveyor.

4. Apparatus as claimed in claim 2 or claim 3, in which the at least one duct is positioned alongside the conveyor, so as to guide the containers as they move along the conveyor, the cooling fluid being directed onto the side walls of the containers.

5. Apparatus as claimed in any one of claims 2 to 4, in which a plurality of ducts define a plurality of channels along which food containers may be moved by the conveyor.

6. Apparatus as claimed in claim 5, in which fastening means are provided on the ducts so that channels, defined by the ducts, may be adjusted to accommodate a plurality of food container sizes.

7. Apparatus as claimed in any one of claims 2 to 6, which further includes means for supplying the cooling fluid to the at least one duct under pressure.

8. Apparatus as claimed in any one of claims 2 to 7, in which apertures are provided on the upper wall of the ducts and which includes a deflector positioned above the apertures of the upper duct wall to deflect cooling fluid onto the containers.

9. Apparatus as claimed in any one of claims 2 to 8, in which the apertures in the ducts are slots.

10. Apparatus as claimed in any one of claims 2 to 9, in which the size of the apertures varies with their position along the length of the ducts.

11. Apparatus as claimed in any one of claims 2 to 10, in which the at least one duct comprises a plurality of independent duct sections.

12. Apparatus as claimed in any one of claims 2 to 11, which includes means for extracting cooling fluid which has been directed onto portions of the containers while they move along the conveyor.

13. Apparatus as claimed in claim 12, in which the cooling fluid extracting means comprises at least one duct having apertures in its wall through which the cooling fluid can pass into the duct.

14. Apparatus as claimed in any one of claims 1 to 13, in which the heat source emits electromagnetic radiation having a wavelength which is greater than about 1 ym.

15. Apparatus as claimed in any one of claims 1 to 14, which further includes means for providing a lid on to the container, downstream along the conveyor of the heat source.

16. A method of producing a food product with a cooked upper surface, which comprises: (a) placing the food product in a container on a conveyor; (b) moving the food product on the conveyor past a heat source; and (c) exposing portions of the container to a cooling fluid while it moves along the conveyor.

17. A method as claimed in claim 16, in which a plurality of food products, in respective containers, are moved on the conveyor past the heat source side-by-side.

18. A method as claimed in claim 16 or claim 17, in which the portions of the container or containers which are exposed to the cooling fluid comprise side wall portions.

19. A method as claimed in any one of claims 16 to 18, in which the conveyor is provided with means for guiding the container or containers along it, and which includes the step of using the guide means to guide the container or containers along the conveyor.

20. A method as claimed in claim 19, in which the guide means comprise hollow ducts with apertures in their side walls, and which includes the step of supplying the cooling fluid to the container or containers through the ducts and the said apertures.

21. A method as claimed in any one of claims 16 to 20, in which the material of the container or containers is a polymeric material.

22. A method as claimed in any one of claims 16 to 21, in which the surface of the food product is heated to at least about 180 C.