System for Multi-Pass Thermal Treating of Food Products

1. Field of the Invention

This invention relates to systems for cooling or heating food products by conveying the food products through a cooling or heating zone.

2. Brief Description of the Prior Art

Food products such as hamburger patties or fish fillets are processed by quick freezing techniques primarily on long continuous conveyor systems. Refrigerated air is typically blown across the product to remove heat. Due to the relatively slow rate of heat transfer these systems require large amounts of conveying surface area to hold substantial quantities of food products for the required duration. These carrying systems can be linear or helical and typically require a substantial amount of space.

A primary object of the present invention is to provide a system for thermal treating of food products with a high rate of heat transfer in a multi-pass continuous process where the products are first surface-treated along a first conveyor course, and then are further processed to complete their thermal treatment in a subsequent conveyor course, or courses, independent of the first course. Another object is to provide such a system where the subsequent conveyor course or courses is or are stacked below the first course so that food products can cascade from the end of one course onto the beginning of a subsequent course. A further object of the present invention is to provide the first course with a thermal contact zone where the food products are conveyed on a thin film sheet across a thermal surface so that the food product side in contact with the thin film will be thermally treated by conduction as it passes across the thermal surface. Still another object is to provide a second or third course where the food products are conveyed through a refrigerated zone for further thermal treatment, being cascaded from one course to another.

These objects and advantages will become apparent from the following description of the invention.

In accordance with these objects and advantages, the invention comprises a multi-pass thermal treating system for food products which comprises at least first and second zones of thermal treatment. A first zone provides a film contact conveyor comprised of a thermal surface, a traveling thin film, a drive for moving the thin film across the thermal surface, and a control for controlling and monitoring the drive. A second zone underlays the first zone and provides a second conveyor comprised of a product conveyor, a second drive for the second conveyor and a second control for controlling and monitoring the second drive, the second conveyor being located such that food products may be cascaded from the traveling thin film downward onto the product conveyor. The second and subsequent conveyors may be film contact conveyors, like the first zone film contact conveyor, or they may be open-mesh endless loop conveyors. The first zone film contact conveyor may be maintained at ambient temperature, an elevated temperature, or a lowered temperature. The subsequent thermal treatment zones are thermal treatment zones that may be film contact conveyors, or updraft, cross-draft or impingement jet air open-mesh endless loop conveyors.

FIG. 1 depicts a three zone system with each zone comprised of a traveling thin film conveyor thermal treatment system;

FIG. 1a is similar to FIG. 1 except that the first and second zones share the same traveling thin film;

FIG. 2 depicts a three zone system with the first zone comprised of a traveling thin film conveyor thermal treatment system and the two subsequent zones comprises of endless loop open-mesh conveyor systems refrigerated with updrafted refrigerated air;

FIG. 3 depicts a three zone system with the first zone comprised of a traveling thin film conveyor thermal treatment system and the two subsequent zones comprised of endless loop open-mesh conveyor systems refrigerated with refrigerated air impingement jets; and

FIG. 4 depicts a three zone system with the first zone comprised of a traveling thin film conveyor thermal treatment system and the two subsequent zones comprises of endless loop open-mesh conveyor systems refrigerated with cross-drafted refrigerated air.

The system of this invention provides a first zone 10 for thermal treatment of food products 12 by transporting the food products on a traveling thin film conveyor 14 where the thin film conveyor moves continuously across a thermal surface 16 to thermally condition the contacting surface of the food products by conduction through the thermal surface 16 and the thin film of the conveyor 14. The system also provides a subsequent zone 18 for thermal treatment of the food products 12 where the products are deposited from the end of the thin film conveyor onto a subsequent conveyor 20 for further thermal treatment. The thermal conditioning occurring in zone 18 may be by thermal conduction or convection, depending on the form of heat transfer mechanism employed in that zone. A subsequent zone 22 for thermal treatment of the food products 12 may also be provided where the products are deposited from the end of conveyor 20 onto a subsequent conveyor 24 for further thermal treatment. The thermal conditioning occurring in zone 22 may be by thermal conduction or convection, depending on the form of heat transfer mechanism employed in that zone. The zones 10 and 18, and 22 if provided, are preferably stacked one below another and arranged so that food products may cascade downward from the end of one conveyor onto the beginning of the subsequent conveyor. Although not shown in the Figures, it would be appropriate for some food products to provide a mechanism for transferring food products from one conveyor to the other, such as a slide or guide or other means, and the transfer could upend the food products as well so that the unprocessed side could be placed side-down on the subsequent conveyor.

In zone 10, a contact table 24 has a flat upper segment that provides the thermal surface 16. The thin film conveyor 14 comprises the thin film 14 provided as an elongated sheet or web that is transported from an infeed supply roll 14a to a take-up roll 14b so that the thin film 14 may be pulled from the infeed roll 14a and wound up on the take-up roll 14b. Food products 12 are deposited onto the thin film 14 at a location immediately adjacent the beginning of the contact table 24 by any suitable means and the film in turn slides across the thermal surface so that, through conduction, heat is transferred between the food products 12 and the thermal surface 16. An appropriate drive mechanism 26 would be coupled to one or both rolls 14a, 14b so as to effect and control the movement of the thin film 14 across the contact table 24. Typically, the drive mechanism would include film guides and a controllable gearmotor driving the take-up roll onto which used film is rolled, and a controller 28 to control the film speed in addition to controlling the starting and stopping of film travel. Typically a variable frequency drive (VFD) will be the means to vary the speed of the gearmotor and consequently the film speed. Since accurate film speed may be critical, systems will typically have a speed monitoring device such as an encoder to feed back speed information to the VFD. This is turn allows automatic adjustments of the gearmotor thus maintaining precise film speed control.

In the case where food products are to be crust frozen on their bottom surfaces, the thermal surface 16 would be a refrigerated surface. This surface may be refrigerated by any of several means, including circuited refrigerant such as ammonia circulated through the contact table 24, cryogens which are sprayed on the underside of the thermal surface 16 within the contact table 24, or cold air blast against the underside of the thermal surface 16 within the contact table 24.

In the case where food products are to be tempered or proofed, such as would be the case for dough products that must be allowed to rise before further processing, the thermal surface 16 could be a heated surface or a surface maintained at ambient temperature. This surface may be heated by any of several means, including circuited warm water circulated through the contact table 24, electric coils within the contact table 24, or warm air blast against the underside of the thermal surface 16 within the contact table 24.

In either of the above two cases, for refrigerating or for heating food products, the first zone 10 provides a film contact conveyor system composed of (a) a thermal surface, (b) a traveling thin film, (c) a drive mechanism for moving the thin film across the thermal surface, and (d) a control system for controlling and monitoring the drive mechanism.

In the case of refrigerating the food products in zone 1, the thin film contact freezer can crust freeze the bottom surface of food products rapidly through a highly efficient solid to solid heat transfer effect. During this phase, food products are carried on the thin continuous film conveyor over the thermal surface cooled to a low temperature on the order of -40.degree. C. to -52.degree. C. Upon contact, the food product's bottom surface begins to freeze instantly. Because of the rapid crust freezing on the flat surface, product deformation and belt markings are avoided. Typically, it only takes about one minute to freeze the product's bottom surface to a depth of one millimeter, a depth sufficient to enable further thermal processing without product deformation of marking. By using a continuous thin film conveyor, impeccable hygiene standards can be achieved due to the single pass usage of the thin film. This form of crust freezing reduces the dehydration effect typically experienced in conventional mechanical freezing systems by up to 50%, thereby increasing product yields. Drip loss of the product when thawed is also dramatically reduced. After usage, the thin film take-up roll can be easily replaced with an empty spool. The leading edge of the new supply roll can either be taped or tied to the trailing edge of the old supply roll. In addition, the freezing area of zone 10 is self-defrosting since frost build-up is continuously removed by the film conveyor and the system can be run for days without stopping to be defrosted. The length of the conveyor in this first zone 10 can be as short as two meters and as long as thirty meters. The system within the first zone 10 can be provided, also, in ten foot modules (3000 mm) and width from 1.5 to 7.2 feet (450 to 2160 mm), with crust freezing capacities varying from 100 to 10,000 pounds per hour (45 to 4500 kilograms per hour). This first zone of contact freezing is particularly well suited for difficult food products that are soft, sticky and wet, or need hand shaping before freezing. Suitable film material for the thin film 14 includes 1/2 mil. polyethylene.

As shown in FIG. 1, the film contact conveyor freezing zone 10 is followed by two additional zones 18 and 20 which are the same as zone 10. Each of these two additional zones includes a film contact conveyor system composed of (a) a thermal surface, (b) a traveling thin film, (c) a drive mechanism for moving the thin film across the thermal surface, and (d) a control system for controlling and monitoring the drive mechanism. The elements within the two additional zones are numbered in multiples of 100 for the elements that are comparable to those of zone 10. Zone 18 elements are a 100 series and zone 22 elements are a 200 series. Whereas the contact film 14 travels from right to left in zone 10, film 114 travels from left to right in zone 18, and film 214 travels from right to left in zone 22. The three zones are stacked one below the other and zone 18 is staggered so that food products 12 from the discharge end of zone 10 will cascade down onto the infeed end of zone 18, and so that the food products 12 from the discharge end of zone 18 will cascade down onto the infeed end of zone 22 as shown in FIG. 1.

Where one or two subsequent zones, such as zones 18 and 22, are also contact film freezers, the discharge from one zone to the next may be designed so that the food products 12 turn over in the process of cascading from zone to zone as shown in FIG. 1. Consequently, where zone 18 crust freezes the bottom of the food products conveyed through the zone, the cascading of the food products turns them so that the crust frozen bottom now becomes the top side in zone 18 and the unfrozen top side in zone 10 becomes the bottom side in zone 18, thereby effecting a crust freezing of that side of the food products. Then, subsequent turning of the food products cascading from zone 18 to zone 22 will turn the food products over a second time and the freezing of the food products is completed in zone 22. Typically, in an arrangement such as depicted in FIG. 1, each zone will effect a portion of the freezing of thin food products such as hamburger patties, so that the first surface is crust frozen in zone 10, the second surface is crust frozen on the opposite side in zone 18, with the remainder frozen in zone 22. This arrangement would work well for fish fillets and chicken breasts, as well as for hamburger patties and similar relatively flat food products. The initial contact freezing that occurs in zone 10 is sufficient to firm the product so that depositing the product on the next conveyor below in zone 18 will not hurt the product.

As shown in FIG. 1a, the third film may be a continuation of the first film, thereby reducing the number of required film drive systems.

FIG. 2 depicts another arrangement of three freezing zones. In this arrangement, the topmost zone 10 is the same as in FIG. 1. The two subsequent zones, however, represent different conveyor configurations suitable for refrigerated air flow from below, up through the bottom-most and up through the intermediate freezing zone. In this arrangement, the intermediate zone 30 and the bottom-most zone 32 provide endless loop open-mesh conveyor belts that convey the food products through the updraft of refrigerated air. The food products in zones 30 and 32 would be contacted on their undersides by the updrafting refrigerated air as they are carried by the open-mesh conveyor belts through the respective zones. In this arrangement, the food products would be cascaded down into the next zone and the cascading could be designed to turn the food products over so that different sides are contacted by the updrafting refrigerated air. Each of the open-mesh conveyor belts, 34, 44, would be controlled by an appropriate drive mechanism, 36 46, and control system, 38, 48. A refrigeration assembly 40 would be located appropriately so that air fans 42 could draft air through the refrigeration coils of the refrigeration assembly for cooling to the desired freezing temperature, and then through the conveyor belts 34, 44.

FIG. 3 depicts another arrangement of three freezing zones. In this arrangement, the topmost zone 10 is the same as in FIG. 1. The two subsequent zones, however, represent different conveyor configurations suitable for refrigerated air impingement flow on the food products simultaneously from above and below along each conveyor product-carrying course. In this arrangement, the intermediate zone 50 and the bottom-most zone 52 provide endless loop open-mesh conveyor belts that convey the food products through the refrigerated air impingement streams. The food products in zones 50 and 52 would be contacted simultaneously on both sides by high velocity impingement refrigerated air streams as they are carried by the open-mesh conveyor belts through the respective zones. In this arrangement, the food products would be cascaded down into the next zone and the cascading could be designed to either turn the food products over or not. Each of the open-mesh conveyor belts, 134, 144, would be controlled by an appropriate drive mechanism, 136, 146, and control system, 138, 148. A refrigeration assembly 150 would be located appropriately so that refrigerated air could be directed into top and bottom impingement sections 152a, 152b and 154a, 154b for each zone. The impingement sections extend across the product-conveying courses and are provided with pluralities of high velocity air outlet jet nozzles distributed across the conveying courses of the intermediate and bottom-most conveyors 134, 144 so that high velocity refrigerated air streams may be directed vertically on both sides of the food products conveyed through zones 50 and 52. The bold arrows pointing to the top and bottom surfaces of the processing course of the conveyors from the impingement sections 152a, 152b and 154a, 145b represent the impingement jet streams from the nozzles.

FIG. 4 depicts another arrangement of three freezing zones. In this arrangement, the topmost zone 10 is the same as in FIG. 1. The two subsequent zones 60, 70, however, represent different conveyor configurations suitable for refrigerated air circulation across the food products along each conveyor product-carrying course. In this arrangement, the intermediate zone 60 and the bottom-most zone 70 provide endless loop open-mesh conveyor belts that convey the food products through the refrigerated air streams. The food products in zones 60 and 70 would be contacted by refrigerated air streams directed from the side across the conveyor belts transversely to the moving path of the conveyor belts as they are carried by the open-mesh conveyor belts through the respective zones. Each of the open-mesh conveyor belts, 334, 344, would be controlled by an appropriate drive mechanism, 336, 346, and control system, 338, 348. A refrigeration assembly 350 would be located appropriately so that air fans 342 could draft air through the refrigeration coils of the refrigeration assembly for cooling to the desired freezing temperature, and then across the conveyor belts 334 from the side, as represented by the arrows. In this arrangement, the food products would be cascaded down into the next zone and the cascading could be designed to turn the food products over so that different sides are contacted by the cross draft of refrigerated air.

While the preferred embodiment of the invention has been described herein, variations in the design may be made. The scope of the invention, therefore, is only to be limited by the claims appended hereto.

The embodiments of the invention in which an exclusive property is claimed are defined as follows: