EP2619514A1

EP2619514A1 - Freeze tunnel and methods of use

Info

Publication number: EP2619514A1
Application number: EP11827267.3A
Authority: EP
Inventors: William Thomas Hockett; Frederick D. Webb; Michael Christopher Metcalf; Robert Joseph Lane
Original assignee: Conagra Foods Lamb Weston Inc
Current assignee: Lamb Weston Inc
Priority date: 2010-09-20
Filing date: 2011-09-16
Publication date: 2013-07-31
Anticipated expiration: 2031-09-16
Also published as: AR083056A1; WO2012040057A4; EP2619514B1; CA2810923A1; WO2012040057A1; US20120067066A1; EP2619514A4

Abstract

A freeze tunnel can have a conveyor configured to move food product from a first end to a second end. At least one first cooling unit and at least one first fan can be positioned on the first side of the conveyor, and at least one second cooling unit and at least one second fan can be positioned on the second side of the conveyor. The fans can cooperate to circulate air inside the freeze tunnel in two opposite rotational directions.

Description

FREEZE TUNNEL AND METHODS OF USE

CROSS REFERENCE TO RELATED APPLICATION

[001] This application claims the benefit of and priority to U.S. Patent Application No. 12/886,428 filed on September 20, 2010, which is incorporated herein in its entirety.

FIELD

[002] This disclosure is directed to a novel freeze tunnel and methods of using the same to at least partially freeze food products, such as sweet potato or other potato products.

BACKGROUND

[003] Freeze tunnels are one way to freeze materials, including food products.

Conventional freeze tunnels include a conveyor belt that transports materials through an enclosure that is maintained at a temperature sufficient to freeze the transported materials. However, such conventional systems suffer from many drawbacks which reduce the efficiency of the system. Accordingly, there is a need for improved efficiency freeze tunnel systems.

SUMMARY

[004] In a first embodiment, a freeze tunnel has a first end and a second end, and a conveyor configured to move food product from the first end to the second end. The conveyor has a first side and a second side. At least one first cooling unit and at least one first fan are positioned on the first side of the conveyor, and at least one second cooling unit and at least one second fan are positioned on the second side of the conveyor. The first and second cooling units are not vertically aligned with the conveyor. The first and second fans cooperate to circulate air inside the freeze tunnel in two opposite rotational directions.

[005] In specific embodiments, the two opposite rotational directions can comprise a first air flow pattern that rotates counter-clockwise when viewed along a longitudinal direction of the freeze tunnel and a second air flow pattern that rotates clockwise when viewed along the longitudinal direction of the freeze tunnel. In the vicinity of the conveyor, the first and second air flow patterns can move in the same general direction. [006] In other embodiments, the first and second cooling units can be positioned in the freeze tunnel at locations lower than the conveyor and the first and second fans can be positioned in the freeze tunnel at locations higher than the conveyor. The first fan can be configured to pull air from an area above the conveyor and blow air downward towards the first cooling unit, while the second fan can be configured pull air from an area above the conveyor and blow air downward towards the second cooling unit.

[007] In certain embodiment, the at least one first cooling unit comprises a plurality of first cooling units that extend substantially along the length of the freeze tunnel, and the at least one second cooling unit comprises a plurality of second cooling units that extend

substantially along the length of the freeze tunnel. The plurality of second cooling units can be positioned generally opposite the plurality of first cooling units relative to the conveyor.

[008] In other embodiments, the freeze tunnel can comprise a first cooling section having at least one of the plurality of first cooling units and at least one of the plurality of second cooling units; a second cooling section having at least one of the plurality of first cooling units and at least one of the plurality of second cooling units; and a third cooling section having at least one of the plurality of first cooling units and at least one of the plurality of second cooling units. A first baffle member can be positioned between the first and second cooling sections and a second baffle member can be positioned between the second and third cooling sections. The first cooling section can comprise a pre-cooling section that has an inner air temperature of between about 40 and 50 degrees Fahrenheit, and the second cooling section can comprise an intermediate cooling section that is configured to freeze an outside surface of the food product.

[009] In other embodiment, the conveyor can comprise a first conveyor that transfers the food product through the first cooling section, a second conveyor that transfers the food product through the second cooling section, and a third conveyor that transfers the food product through the third cooling section. The freeze tunnel can comprise a product exchange between the second and third conveyor, which causes the food product to be shaken up to reduce clumping. The second cooling section can include a temperature adjustment member that can adjust the temperature of the second cooling section to a temperature at which the outside surface of the food product will freeze just before the food product reaches the product exchange between the second and third conveyors. The adjustable temperature range of the second cooling section can be between about 20 and 60 degrees Fahrenheit. The temperature adjustment member can be a device for changing the temperature of the second cooling section while the freeze tunnel is in operation.

[010] In another embodiment, a method of freezing a food product is provided. The method comprising advancing the food product into a freeze tunnel on a conveyor. A first cooling unit can be provided on a first side of the conveyor and a second cooling unit can be provided on a second side of the conveyor. Air can be circulated through the first cooling unit and towards the conveyor in a first air flow pattern and through the second cooling unit and towards the conveyor in a second air flow pattern. The first and second air flow patterns can be rotationally opposite from one another. In some embodiments, the first and second air flow patterns can be in the same general direction as air from the first and second air flow patterns collectively passes through the conveyor.

[011] In other embodiments, a first fan can be provided on the first side of the conveyor and a second fan can be provided on the second side of the conveyor. The first and second fans can circulate air in the freeze tunnel in the first and second air flow patterns, respectively, and air from both the first and second air flow patterns can move collectively upwards through the conveyor.

[012] In other embodiments, a plurality of the first cooling units can be provided on the first side of the conveyor and a plurality of second cooling units can be provided on the second side of the conveyor. The first and second cooling units can extend substantially the length of the freeze tunnel. The food product can be advanced through a first cooling section that has an internal temperature of between about 40 and 50 degrees Fahrenheit and through a second cooling section that is maintained at a temperature that causes an outside surface of the food product to freeze. The food product can also be advanced through a third cooling section to further freeze the food product. In certain embodiments, the conveyor can comprise at least a first and second conveyor. Food product can be transferred from a first conveyor to a second conveyor immediately after the outside surface of the food product is frozen in the second cooling section. In certain embodiments, the temperature of the second cooling section can be adjusted in real time to ensure that the outside surface of the food product freezes before the food product is transferred from the first conveyor to the second conveyor.

[013] In some embodiments, the outside surface of the food product comprises an oil layer from a process step performed prior to entry of the food product into the freeze tunnel (e.g., frying, parfrying). The solidification of the outside of surface can comprise solidification of the entire oil layer or at least a portion of the oil layer.

[014] In another embodiment, a freeze tunnel has a first longitudinal half and a second longitudinal half extending the length of the freeze tunnel. The freeze tunnel comprises a transport means for moving food product through the freeze tunnel. The transport means can have a portion in the first longitudinal half and a portion in the second longitudinal half of the freeze tunnel. A first cooling means for reducing the temperature in the freeze tunnel can be positioned in the first longitudinal half and a second cooling means for reducing the temperature in the freeze tunnel can be positioned in the second longitudinal half. The freeze tunnel can include a first air flow means for causing a first air flow pattern in the first longitudinal half and a second air flow means for causing a second air flow pattern in the second longitudinal half. The first and second air flow patterns can be in rotationally opposite directions.

[015] In certain embodiments, the first cooling means comprises a plurality of first cooling units that extend along a length of the freeze tunnel, and the second cooling means comprises a plurality of second cooling units that extend along the length of the freeze tunnel. The plurality of first cooling units can be positioned generally opposite the plurality of second cooling units. The first air flow pattern can comprise a counter-clockwise rotation when viewed in a longitudinal direction from an entrance side of the freeze tunnel and the second air flow pattern can comprise a clockwise rotation when viewed in the longitudinal direction from the entrance side of the freeze tunnel. In other embodiments, the freeze tunnel can comprise a first cooling section, a second cooling section, and a third cooling section. The first cooling section can be separated from the second cooling section by a baffle and the second cooling section can be separated from the third cooling section by a baffle. The second cooling section can include a temperature adjustment means for adjusting the temperature of the second cooling section during operation of the freeze tunnel.

[016] The foregoing and other objects, features, and advantages of the disclosed

embodiments will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[017] FIG. 1 is a perspective view of a novel freeze tunnel system.

[018] FIG. 2 is a top view of the freeze tunnel system shown in FIG. 1.

[019] FIG. 3 is a side view of the freeze tunnel system shown in FIG. 1.

[020] FIG. 4 is a cross-sectional view of a portion of the freeze tunnel system shown in FIG. 1, illustrating novel air flow patterns within the freeze tunnel and a novel configuration of cooling units.

[021] FIG. 5 is a fluid flow model illustrating air flow within a novel freeze tunnel system.

[022] FIG. 6 is a fluid flow model illustrating air flow within a novel freeze tunnel system and between two side walls.

[023] FIG. 7 is a top, schematic view of a novel freeze tunnel system with a plurality of conveyors and a plurality of cooling sections.

[024] FIG. 8 is a side, schematic view of the novel freeze tunnel system shown in FIG. 7.

DETAILED DESCRIPTION

[025] The following description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Various changes to the described embodiment may be made in the function and arrangement of the elements described herein without departing from the scope of the invention. [026] As used in this application and in the claims, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. Additionally, the term "includes" means "comprises." Further, the terms "coupled" and "associated" generally mean electrically, electromagnetically, and/or physically (e.g., mechanically or chemically) coupled or linked and does not exclude the presence of intermediate elements between the coupled or associated items absent specific contrary language.

[027] Although the operations of exemplary embodiments of the disclosed method may be described in a particular, sequential order for convenient presentation, it should be understood that disclosed embodiments can encompass an order of operations other than the particular, sequential order disclosed. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Further, descriptions and disclosures provided in association with one particular embodiment are not limited to that embodiment, and may be applied to any embodiment disclosed.

[028] Moreover, for the sake of simplicity, the attached figures may not show the various ways (readily discernable, based on this disclosure, by one of ordinary skill in the art) in which the disclosed system, method, and apparatus can be used in combination with other systems, methods, and apparatuses. Additionally, the description sometimes uses terms such as "produce" and "provide" to describe the disclosed method. These terms are high-level abstractions of the actual operations that can be performed. The actual operations that correspond to these terms can vary depending on the particular implementation and are, based on this disclosure, readily discernible by one of ordinary skill in the art.

[029] FIGS. 1-3 illustrate various views of a freeze tunnel system 10 that has a first end 12 and a second end 14. Freeze tunnel 10 is configured to receive materials, such as food product, in the first end 12, transport them the length of freeze tunnel 10, and then deliver them out the second end 14. At least one conveyor 16 (e.g., an endless or continuous conveyor belt) can be provided to transport the food items between the first end 12 and the second 14.

[030] Referring to FIG. 4, a cross-sectional view of freeze tunnel system 10 illustrates a conveyor 16 that extends generally along a center of the width of freeze tunnel 10. Preferably, conveyor 16 extends the length of freeze tunnel 10 to transport product from the first end 12 to the second end 14 (FIG. 1). A first cooling unit 20 can be positioned on a first side 22 of conveyor 16 and a second cooling unit 24 can be positioned on a second side 26 of conveyor 16. As shown in FIG. 4, first and second cooling units 20, 24 are preferably not vertically aligned with conveyor 16. Instead, they are preferably spaced apart from the vertical position of conveyor 16.

[031] Many conventional systems are configured with a cooling unit vertically aligned with the conveyor belt. A vertically aligned cooling unit can be positioned either above or below the conveyor belt. However, such conventional systems can result in contamination of the food product to be frozen and/or contamination of the cooling system itself. For example, if the cooling unit is positioned above the conveyor belt, the cooling unit can drip or leak onto the food product as it passes below the overhead cooling system. Such contamination of food product is very undesirable. Even if the cooling unit is only dripping water and/or vapor, which may not render the food product inedible, the freezing process of the food product can be adversely affected by the exchange of moisture from the cooling unit to the food product.

[032] If the cooling unit is positioned directly below the conveyor belt (e.g., vertically aligned), the cooling unit can be contaminated by oil and other debris that may fall though the conveyor belt onto the cooling unit. Such debris can adversely affect the operation of the cooling unit, reducing the cooling efficiency of the system and increasing the required downtime for cleaning the cooling unit.

[033] In contrast, the illustrated embodiment spaces cooling units 20, 24 apart from conveyor 16 so that they are not vertically aligned and directly above or underneath conveyor 16. Thus, undesired moisture from the cooling units will not fall onto the conveyor from the cooling units, and oil and other debris (solid or liquid) will not fall through the conveyor onto the cooling units 20, 24. Instead, such debris will simply fall through the conveyor onto the floor (or other collection area) without adversely impacting the operation and function of the cooling units 20, 24.

[034] In addition, by arranging cooling units on opposing sides of conveyor 16,

improvements in the air flow and circulation in freeze tunnel 10 can be achieved, which facilitates uniform cooling of food product regardless of the location of the product across the belt. For example, by positioning first cooling unit 20 on the first side 22 of the conveyor 16 and second cooling unit 24 on the second side 26 of the conveyor 16, air flowing from the cooling units can be more uniformly distributed across the width of the conveyor 16 to produce a more consistent temperature across the conveyor.

[035] In conventional freeze tunnels or cooling systems, a single cooling unit may be positioned near the conveyor. However, because the cooling unit must be positioned closer to one area or region of the conveyor than another, it is difficult to provide consistent air flow across the entire width and length of the conveyor. Thus, single cooling unit systems generally produce regions that vary in temperature and air flow across the conveyor. Such variations can result in non-uniform cooling of product on the conveyor, which may require that the entire system be cooled to a lower temperature to ensure complete cooling of product transported in the warmer zones across the conveyor. However, since the energy required by the system is greatly impacted by the temperature of the cooling medium, it is not very efficient to require cooling units to operate at lower temperatures to account for inconsistent cooling distributions in the freeze tunnel. Accordingly, it is desirable to improve the air flow patterns so that there are fewer variations in temperatures and air flow across the width of the conveyor.

[036] To counter such air flow variation, some conventional systems employ baffles, such as perforated sheet metal, that attempt to even air flow across the belt by restricting air flow in some areas (e.g., by having smaller or fewer perforations in the baffle) and encouraging air flow in other areas (e.g., by having larger or more perforations in the baffle). Although these structures can provide more uniform cooling across a conveyor, the restriction of air flow by the baffles reduces the total air flow across the conveyor, which, in turn, reduces the efficiency of the freeze tunnel.

[037] In contrast, by providing cooling units 20, 24 on opposing sides of conveyor 16 as shown in FIG. 4, air can flow more uniformly across the width of conveyor 16. In particular, air flow within freeze tunnel 10 can be configured to flow in two different rotation patterns along a cross-section of freeze tunnel 10. For example, in the illustrated embodiment, the two opposing cooling units 20, 24 cause air to circulate within freeze tunnel 10 in a first air flow pattern 40 and a second air flow pattern 42, with the first and second air flow patterns being rotationally opposite. For example, as shown in FIG. 4, first air pattern 40 can be a generally counterclockwise flow pattern and second air flow pattern 42 can be a generally clockwise flow pattern.

[038] To facilitate the flow of air in the two different rotational patterns, one or more fans can be provided. For example, as shown in the illustrated embodiment, a first fan 30 can be positioned on the same side as first cooling unit 20 and a second fan 32 can be positioned on the same side as second cooling unit 24. First fan 30 can pull air from a central region in the freeze tunnel and direct it downwards and through first cooling unit 20. Similarly, second fan 32 can pull air from a central region in the freeze tunnel and direct it downwards and through second cooling unit 24. Air exiting the first and second cooling units 20, 24, can meet and be directed upward through conveyor 16. After passing through conveyor 16, the air can move upward, where it is pulled towards the first side 22 or second side 26 of the conveyor by the first and second fans, 30, 32, respectively, to complete the circuit of the air flow patterns 40, 42.

[039] Accordingly, as shown in FIG. 4, first and second fans 30, 32 cooperate to produce rotationally opposite air flow patterns. In addition, the two different air flow patterns 40, 42 can be generally separated into two areas of the freeze tunnel as viewed in a longitudinal direction (e.g., from the entrance side as shown in FIGS. 4 and 5). Thus, the first air flow patterns 40 is generally constrained or provided in a first longitudinal half of the freeze tunnel (e.g., the left half of the freeze tunnel as shown in FIGS. 4 and 5) and second air flow patterns 42 is generally constrained or provided in a second longitudinal half of the freeze tunnel (e.g., the right half of the freeze tunnel as shown in FIGS. 4 and 5). An imaginary line (not shown) splitting the freeze tunnel 10 in half can be considered to be the division between the two air flow patterns. Of course, some air flow will overlap between the two halves near the imaginary line splitting the freeze tunnel; however, for the most part, the two halves of the freeze tunnel can be considered to have different rotational air flow patterns.

[040] In addition, as shown in FIGS. 4 and 5, conveyor 16 is also generally bisected by the imaginary line, which means that half of conveyor 16 is in the first air flow pattern 40 and the other half of conveyor 16 is in the second air flow pattern 42. By directing air from the two air flow patterns so that half of the conveyor receives air from the first air flow pattern (which is cooled by the first cooling unit) and half of the conveyor receives air from the second air flow pattern (which is cooled by the second cooling unit), cooling temperatures across the conveyor can be relatively uniform.

[041] As shown in FIG. 4, although the air from the two air flow patterns 40, 42 are in different (e.g., opposite) rotational patterns, preferably air from both the first and second air flow patterns passes through the conveyor 16 moving in the same general direction. For example, as shown in the illustrated embodiment of FIG. 4, air from both the first and second air flow patterns 40, 42 travels through conveyor 16 (and any product placed on conveyor 16) in the same upwards direction. By directing air in a common direction as it passes through conveyor 16, it is possible to improve the uniformity of air flow while eliminating the potential for competing air flow that would occur if the air from the two flow paths traveled in opposing directions in the vicinity of the conveyor.

[042] FIGS. 5 and 6 illustrate fluid flow modeling results for freeze tunnel 10. As shown in FIG. 5, the two air flow patterns 40, 42 provide relatively uniform air flow across the width of conveyor 16. Conveyor 16 comprises a top surface 16a and a bottom surface 16b. Top surface 16a is configured to carry and convey the food product (or other material to be frozen). The food product 19 is schematically represented in FIG. 5. However, it should be understood that food product 19 can comprise various materials or items positioned on a top surface of conveyor 16, including, for example, one or more layers of loosely piled food items, such as french fries or sweet potato fries that have been cut and at least partially fried before entering freeze tunnel 10.

[043] As shown in FIG. 5, air approaching bottom surface 16b from below is quite uniform in air flow speeds across the width of conveyor 16. For example, air flow towards conveyor 16 can vary by less than about 100 ft/min across the width of the conveyor, such as between about 360 and 460 ft/min. Similarly, as air flow is drawn towards fans 30, 32, it can also be relatively uniform and vary by the same amount above. For example, air flow moving towards the fans can vary by about 100 ft/min and have a velocity between about 360 and 460 ft/min. [044] FIG. 6 illustrates another fluid flow modeling result for freeze tunnel 10. FIG. 6 shows air flow velocities across the width of freeze tunnel 10. As shown in FIG. 6, a central portion 50 of freeze tunnel 10, which is where the conveyor is positioned, experiences relatively uniform air flow throughout its width. For example, in this model, air flow can be between about 400 and 440 ft/min across a middle area of the freeze tunnel 10. In the central portion 50, it can be even more uniform, with a range of less than about 20 ft/min across the entire width of the central portion 50 (e.g., across conveyor 16), such as is the case with a range between about 400 and 420 ft/min.

[045] To facilitate the reverse rotational flows shown in FIG. 4, fans 30, 32 can be powered in the same general direction relative to conveyor 16. For example, as shown in the illustrated embodiment of FIG. 4, when first fan 30 is directed downward, second fan 32 can also be directed downward. Fans 30 and 32 are preferably not directed at each other, to reduce the amount of turbulent air flow in the rotational air flow patterns. However, it should be understood that reverse rotational flow patterns, such as those described above, can be achieved by directing both first fan 30 and second fan 32 in various directions, including towards conveyor 16 (i.e., in the same direction relative to the conveyor).

[046] As shown in FIG. 4, first and second fans 30, 32 are preferably powered by motors 46 that are positioned outside of the side walls 48 of freeze tunnel 10. By positioning motors 46 (and other heat- generating elements associated with first and second fans 30, 32) outside of freeze tunnel 10, the heat generated by these elements can be dissipated in the ambient air surrounding freeze tunnel 10 rather than inside freeze tunnel 10. By reducing the amount of heat generated within freeze tunnel 10, the efficiency of the system can be further increased.

[047] FIG. 7 illustrates a top cross-sectional view of freeze tunnel 10. As shown in FIG. 7, a plurality of pairs of cooling units 20, 24 and first and second fans 30, 32 can extend the length of freeze tunnel 10. As shown in FIG. 7, arrows are shown in the cooling units to indicate the direction of air flow through the cooling unit. Thus, the reverse rotational air flow patterns shown in FIG. 4 can be provided along the length of freeze tunnel 10. Each of these pairs of cooling units 20, 24 and first and second fans 30, 32 can be configured to cooperate with one another. Thus, for example, each pair of cooling units and first and second fans can be positioned on opposite sides of conveyor 16 in an opposing relationship with one another.

[048] As shown in FIGS. 7 and 8, freeze tunnel 10 can be configured with a plurality of cooling stages or sections. In the illustrated embodiment, freeze tunnel 10 comprises a first cooling section 60, a second cooling section 62, and a third cooling section 64. First cooling section 60 can be configured as a "pre-cool" stage and the air temperature within first cooling section can be significantly higher than that of the other two sections. The lower the temperature of the cooling section, the higher the amount of energy required to maintain that temperature. When cooling product that enters freeze tunnel 10 at a temperature above normal room temperature, as is the case with a recently-fried food product (e.g., french fries, sweet potato fries), then the temperature difference between the food product entering the first cooling section and the temperature inside the first cooling section is more than sufficient to efficiently reduce the temperature of the food product. Thus, for example, the pre-cool stage can comprise cooling units that are cooled to a temperature of between about 35 and 55 degrees Fahrenheit, or more preferably between about 40 and 50 degrees

Fahrenheit. In some embodiments, the temperatures in the pre-cooling stage can be selected so that an outside surface of the food product is cooled to a temperature approaching the solidification point, but not below the solidification point.

[049] In one embodiment, the medium of the cooling units in the first stage is water at about 45 degrees Fahrenheit. The water medium can be cooled using recycled heat that is captured from other high energy sources. Since the temperatures of the pre-cooling section are relatively high, it can be convenient to power the pre-cooling section using recovered waste energy. For example, excess heat can be captured from a large scale fryer and used to cool the water that circulates in the cooling units of the first stage. Various techniques can be provided to convert the captured steam into usable energy for reducing the temperature of the cooling medium (e.g., water) in the pre-cooling section. For example, the recaptured steam energy can be used in combination with an absorption chiller that can remove heat from the cooling medium to reduce the temperature of the cooling medium. Alternatively, the recaptured steam energy can be converted to electricity (e.g., using a steam turbine or other electricity generating source) that can then be used to reduce the temperature of the cooling medium by other conventional means.

[050] Although some conventional systems provide an ambient air system for initially cooling food product that is at an elevated temperature, the ambient temperatures in most plants can vary significantly depending on time (e.g., night or day) and season (e.g., winter or summer). Accordingly, ambient temperatures are not uniform and can introduce

inconsistency into the freezing process. In contrast, the pre-cooling stage described herein can be configured to operate at a consistent temperature that will not vary significantly depending on the time of day or season in which the operation is taking place.

[051] Product can leave first cooling section 60 and enter second cooling section 62.

Second cooling section is preferably configured to cool the product to a temperature lower than that of first cooling section 60. Thus, if first cooling section 60 comprises a pre-cool section that has a temperature of about 45 degrees Fahrenheit, second cooling section 62 can be configured to have a temperature that is significantly lower than 45 degrees Fahrenheit. Similarly, product can leave second cooling section 62 and enter third cooling section 64, which is configured to cool the product to a temperature lower than that of second cooling section 62.

[052] A plurality of baffle members 72 can be positioned between cooling sections to reduce the flow of air from one cooling section to an adjacent cooling section. Baffle members 72 can comprise insulated wall structures that generally separate adjacent cooling sections from one another. Thus, for example, baffles 72 can be positioned between first and second cooling section 60, 62 and between second and third cooling sections 62, 64. Baffles 72 can extend generally across the width of an inside area of freeze tunnel 10 and from a top portion to a lower portion to restrict air movement between the separated, adjacent sections. Preferably, baffles 72 extend downwards towards conveyor 16, providing enough clearance that product can pass under baffles 72 without contacting them.

[053] In addition, as shown in FIGS. 7 and 8, conveyor 16 can comprise a plurality of conveyors. For example, as shown in the illustrated embodiment, a first conveyor 66, a second conveyor 68, and third conveyor 70 can collectively operate to transport a material from the first end 12 to the second end 14 of freeze tunnel 10. As shown in FIG. 8, baffles 72 can be positioned just after food product is transferred to the next, adjacent conveyor.

[054] Multiple conveyors provide several advantages. First, they reduce the total amount of weight that any one conveyor must support. Second, the transfer of product between conveyors allows the product to be shaken or separated to prevent clumping of sticking together of product. This can be particularly useful when freezing product that contains oils (or other liquids), such as french fries or sweet potato fries that have recently been at least partially fried. The product transfer or exchange between the two conveyors can comprise a change in height or drop-off that causes the product to be shaken or separated.

[055] In one embodiment, second cooling section 62 can be operated at a temperature sufficient to "set-up" the food product just before the food product is transferred from the second cooling section 62 to the third cooling section 64. "Setting-up" occurs as the oil (or other liquid) on the outside of the food product solidifies. Thus, for example, as the oil solidifies on the surface of a partially- fried food product, adjacent product will clump together. The second cooling section preferably is configured to provide adequate cooling to reduce the temperature of an outside surface of the food product to a temperature that is lower than the surface oil's solidification point. Also, it is desirable to arrange the location of the transfer between the second and third cooling sections 62, 64 so that the product will be transferred just as the outside surface of the product is adequately cooled and/or solidified. By transferring the product just at or after it is "set-up," the product can be separated, thereby reducing clumping or grouping of food product that is frozen together. The physical separation and reshuffling of food pieces from each other while being transferred from one conveyor to another can help reduce the likelihood that oil on the surfaces of the individual food pieces will contact other individual food pieces and undesirably cause those food pieces to be frozen together as the food product leaves the freeze tunnel.

[056] In one embodiment, second cooling section 62 comprises an adjustable temperature control to vary the temperature in second cooling section 62. The adjustable temperature control can vary the temperature of the second cooling section 62 in real time while the freeze tunnel 10 is in operation. Thus, in real time, an operator can adjust the temperature in second cooling section 62 until the "set-up" of product occurs just prior to the transfer of product from second conveyor 68 to third conveyor 70. The adjustable temperature control can be, for example, a device that alters the suction pressure on the coil, thereby allowing pull more or less ammonia to be drawn into the cooling units in the second cooling section.

[057] It can be particularly useful vary the temperature of the second cooling section in real time to account for a variation in "set-up" temperatures caused by, for example, the use of different oils on the surface of a food product, different surfaces areas or shapes caused by the type of cut, size, or shape of the food product, and different stacking densities. Each of these elements, and other similar variations in the product being frozen, can vary the temperature at which an outside surface of the food product will freeze or "set-up." Thus, by being able to readily adjust the temperature of the second freezing zone, the system can be adjusted to process various food products efficiently and without significant clumping or clustering of the product.

[058] In one embodiment, the first cooling section can be cooled to about 45 degrees Fahrenheit (as described above), second cooling section can be cooled to about 10 - 60, and more preferably 20 - 60 degrees Fahrenheit, and third cooling section can be cooled to less than about 0 degrees Fahrenheit and more preferably to less than about -20 degrees

Fahrenheit. Thus, in each section, the product temperature (e.g., outside product temperature) can be reduced to about 85 degrees Fahrenheit in the first cooling section, about 60 degrees Fahrenheit in the second cooling section, and about 10 degrees Fahrenheit in the third cooling section.

[059] Product bed depth across the first, second, and third conveyors can also vary. For example, to further reduce the amount of clumping that may occur within the second cooling section, the product depth on the second conveyor 68 can desirably be less than the product depth on the first and third conveyors. In one embodiment, for example, product depth on the first and third conveyors can be about 3-5 inches, while the product depth on the second conveyor is less than about 3 inches.

[060] Various methods can be used to independently vary the product depths on the different conveyors. For example, the belt speeds of the different conveyors can be independently controlled to adjust the bed depths of each respective conveyor. Thus, increasing the belt speed on a conveyor provides a shallower product depth and decreasing the belt speed on a conveyor provides a deeper product depth.

[061] Changes in belt speed also effect the residence time of product in the cooling sections of the respective conveyors. Thus, increasing belt speed on one particular belt not only decreases product depth on that belt, it also decreases the time that product remains in the cooling section associated with that belt. Accordingly, it is desirable to take both product depth and residence times in the respective cooling sections into consideration when selecting the operating belt speed for each conveyor.

[062] In one embodiment, for example, the first conveyor is configured to operate at a speed that provides a product depth and residence time that is sufficient to cool an outside surface of the product to a temperature approaching the solidification point of the oil on the surface of the food product. The second conveyor is configured to operate at a speed that provides a product depth and residence time sufficient to cool an outside surface of the food product to a temperature below the solidification point of the oil on the surface of the food product. The third conveyor is configured to operate at a speed that provides a product depth and residence time that is sufficient to freeze the product in its entirety. Each conveyor can operate independently of the other conveyors so that each conveyor can operate at different speeds to accomplish the desired product depths and residence times of its respective cooling section.

[063] In some embodiments, the conveyor can comprise a plastic belt. By using a plastic belt for each of the first, second, and third conveyors, the temperature of product stacked on the belt can be more uniform. For example, conventional metal belt systems transfer temperature readily, causing product that is in contact with the belt to be significantly colder than product that is not in contact with the belt. Thus, there can be a great variation in the temperature of product that is stacked on the belt. In contrast, plastic belts do not transfer temperature so easily and therefore, the temperature of product on the belt can be more uniform. One such plastic belt that is available is KVP® Straight 2" pitch belting (FF620 Fluid-Flo), available from KVP in Reading, PA.

[064] Since the three cooling stages can be configured to operate at different temperatures, the cooling units in each stage can vary in size and structure. For example, as shown in the illustrated embodiment of FIG. 7, the cooling units in the first stage are smaller than the cooling units in the second stage, which are, in turn, smaller than the cooling units in the third stage. In addition, the cooling units can be configured to receive different cooling mediums. For example, as discussed above, water can be the cooling medium of first cooling section 60. The cooling units in the second and third cooling sections can be cooled by ammonia to the desired cooling temperature, down to a temperature of about -28 degrees Fahrenheit.

[065] Another advantage of providing the cooling units so they are in a vertical

configuration that is spaced-apart from vertical alignment with conveyor 16 is that the freeze tunnel system 10 can be more easily cleaned using clean-in-place (CIP) technology. For example, referring again to FIG. 1, a plurality of hoses 80 can be coupled to piping 82 for the delivery of cleaning fluids to the interior of freeze tunnel 10. In particular, hoses 80 can extend into the interior of freeze tunnel and can be configured to spray cleaning fluids onto the conveyor and other areas inside the freeze tunnel that require cleaning. Additional piping 84 (FIG. 3) can be provided to collect cleaning fluids from the lower portion of the freeze tunnel after the freeze tunnel has been cleaned. If desired, the piping 82, 84 can also be used to deliver defrosting materials to coils of the cooling units inside the freeze tunnel.

[066] If defrosting is to be performed, it is preferably performed before the CIP cleaning process. To further clean the freeze tunnel, it can be desirable to spray the desired cleaning fluids into the interior of the freeze tunnel and then heat the tunnel by delivering a high temperature fluid into coils of the cooling units. Thus, the cooling units can be operated to heat the inside of the freeze tunnel.

[067] In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.

Claims

We claim:

1. A freeze tunnel comprising:

a first end and a second end;

a conveyor configured to move a plurality of individual pieces of food product from the first end to the second end, the conveyor having a first side and a second side;

at least one first cooling unit and at least one first fan positioned on the first side of the conveyor; and

at least one second cooling unit and at least one second fan positioned on the second side of the conveyor,

wherein the at least one first and the at least one second cooling units are not vertically aligned with the conveyor, and the at least one first and second fan cooperate to circulate air inside the freeze tunnel in two opposite rotational directions.

2. The freeze tunnel of claim 1, wherein the two opposite rotational directions comprise a first air flow pattern that rotates counter-clockwise when viewed along a longitudinal direction of the freeze tunnel and a second air flow pattern that rotates clockwise when viewed along the longitudinal direction of the freeze tunnel, and

wherein, in the vicinity of the conveyor, the first and second air flow patterns move in the same general direction.

3. The freeze tunnel of claim 1, wherein the at least one first and second cooling units are positioned in the freeze tunnel at locations lower than the conveyor and the at least one first and second fans are positioned in the freeze tunnel at locations higher than the conveyor.

4. The freeze tunnel of claim 3, wherein the at least one first fan is configured to pull air from an area above the conveyor and to blow the air downward towards the at least one first cooling unit, and the at least one second fan is configured to pull air from an area above the conveyor and to blow the air downward towards the at least one second cooling unit.

5. The freeze tunnel of claim 1, wherein the at least one first cooling unit comprises a plurality of first cooling units that extend substantially along the length of the freeze tunnel, and the at least one second cooling unit comprises a plurality of second cooling units that extend substantially along the length of the freeze tunnel, the plurality of second cooling units being positioned generally opposite the plurality of first cooling units relative to the conveyor.

6. The freeze tunnel of claim 5, comprising:

a first cooling section having at least one of the plurality of first cooling units and at least one of the plurality of second cooling units;

a second cooling section having at least one of the plurality of first cooling units and at least one of the plurality of second cooling units;

a third cooling section having at least one of the plurality of first cooling units and at least one of the plurality of second cooling units; and

a first baffle member positioned between the first and second cooling sections and a second baffle member positioned between the second and third cooling sections.

7. The freeze tunnel of claim 6, wherein the first cooling section comprises a pre- cooling section that has an inner air temperature of between about 40 and 50 degrees

Fahrenheit at an exit end, and the second cooling section comprises an intermediate cooling section that is configured to cool an outside surface of the pieces of food product to a temperature below a solidification point of oil on the outside surface of the pieces of food product.

8. The freeze tunnel of claim 7, wherein the conveyor comprises a first conveyor that transfers the food product through the first cooling section, a second conveyor that transfers the food product through the second cooling section, and a third conveyor that transfers the food product through the third cooling section, the freeze tunnel further comprising:

a product exchange between the second and third conveyor causes the pieces of food product to be shaken up to reduce clumping that is caused by the solidification of oil on the surfaces of adjacent pieces of food product.

9. The freeze tunnel of claim 8, wherein the second cooling section comprises a temperature adjustment member that can adjust the temperature of the second cooling section to a temperature at which the oil on the outside surface of pieces of the food product will solidify before the food product reaches the product exchange between the second and third conveyors, and

wherein the adjustable temperature range of the second cooling section is between about 20 and 60 degrees Fahrenheit.

10. The freeze tunnel of claim 9, wherein the temperature adjustment member comprises a device for changing the temperature of the second cooling section while the freeze tunnel is in operation.

11. A method of freezing individual pieces of food product, the method comprising:

advancing the food product into a freeze tunnel on a conveyor; providing a first cooling unit on a first side of the conveyor and a second cooling unit on a second side of the conveyor;

circulating air through the first cooling unit and towards the conveyor in a first air flow pattern; and

circulating air through the second cooling unit and towards the conveyor in a second air flow pattern,

wherein the first and second air flow patterns are rotationally opposite from one another.

12. The method of claim 11, wherein the first and second air flow patterns are in the same general direction as air from the first and second air flow patterns collectively passes through the conveyor.

13. The method of claim 11, further comprising:

providing a first fan on the first side of the conveyor and a second fan on the second side of the conveyor,

wherein the first and second fans circulate air in the freeze tunnel in the first and second air flow patterns, respectively, and air from both the first and second air flow patterns moves collectively upwards through the conveyor.

14. The method of claim 11, further comprising:

providing a plurality of the first cooling units on the first side of the conveyor and a plurality of second cooling units on the second side of the conveyor, the first and second cooling units extending substantially the length of the freeze tunnel;

advancing the food product through a first cooling section, the first cooling section having an internal temperature of between about 40 and 50 degrees Fahrenheit;

advancing the food product through a second cooling section, the second cooling section being maintained at a temperature that causes an outside surface of pieces of food product to freeze; and

advancing the food product through a third cooling section to substantially freeze the entirety of the pieces of food product.

15. The method of claim 14, wherein the conveyor comprises at least a first, second, and third conveyor, the method further comprising:

transferring the pieces of food product from the first conveyor to the second conveyor before the outside surfaces of the pieces of food product are frozen;

transferring the pieces of food product from the second conveyor to the third conveyor immediately after the outside surfaces of the pieces of food product are frozen in the second cooling section.

16. The method of claim 15, further comprising:

independently controlling depths of the food product on the first, second, and third conveyors.

17. The method of claim 15, further comprising:

adjusting the temperature of the second cooling section in real time to ensure that the outside surfaces of the pieces of food product solidify before the pieces of food product are transferred from the first conveyor to the second conveyor.

18. A freeze tunnel having a first longitudinal half and a second longitudinal half extending the length of the freeze tunnel, the freeze tunnel comprising:

a transport means for moving food product through the freeze tunnel, the transport means having a portion in the first longitudinal half and a portion in the second longitudinal half of the freeze tunnel;

a first cooling means for reducing the temperature in the freeze tunnel, the first cooling means being positioned in the first longitudinal half;

a second cooling means for reducing the temperature in the freeze tunnel, the second cooling means being positioned in the second longitudinal half;

a first air flow means for causing a first air flow pattern in the first

longitudinal half; and

a second air flow means for causing a second air flow pattern in the second longitudinal half;

wherein the first and second air flow patterns are in rotationally opposite directions.

19. The freeze tunnel of claim 18, wherein the first cooling means comprises a plurality of first cooling units that extend along a length of the freeze tunnel, and the second cooling means comprises a plurality of second cooling units that extend along the length of the freeze tunnel, and

wherein the plurality of first cooling units are positioned opposite the plurality of second cooling units.

20. The freeze tunnel of claim 19, wherein the first air flow pattern comprises a counter-clockwise rotation when viewed in a longitudinal direction from an entrance side of the freeze tunnel and the second air flow pattern comprises a clockwise rotation when viewed in the longitudinal direction from the entrance side of the freeze tunnel.

21. The freeze tunnel of claim 20, wherein the freeze tunnel comprises a first cooling section, a second cooling section, and a third cooling section, and the first cooling section is separated from the second cooling section by a baffle and the second cooling section is separated from the third cooling section by a baffle, and

wherein the second cooling section comprising a temperature adjustment means for adjusting the temperature of the second cooling section during operation of the freeze tunnel.