WO1991014380A1

WO1991014380A1 - Method and apparatus for dewatering food products

Info

Publication number: WO1991014380A1
Application number: PCT/SE1991/000236
Authority: WO
Inventors: Åke SKAGMO
Original assignee: Frigoscandia Food Process Systems Ab
Priority date: 1990-03-29
Filing date: 1991-03-27
Publication date: 1991-10-03
Also published as: SE9001159D0; SE9001159L; AU7589891A; SE465996B

Abstract

A method for dewatering food products forming a product bed, and an apparatus for carrying out the method. The apparatus is characterised by a means arranged transversely of the product bed adjacent to the second dewatering zone and forming a fluidisation zone. A fan (56) produces such a gas flow from below through the product bed that the products in this zone are fluidised and evenly distributed.

Description

METHOD AND APPARATUS FOR DEWATERING FOOD PRODUCTS

The present invention relates to the dewatering of food products, especially after blanching or washing or, for example, after quality rating of peas by means of salt water, prior to refrigeration of the food products.

Before refrigeration, food products, such as diced beefsteak tomatoes, sliced carrots and peas, must be pre- treated in different ways in order to keep or be made more attractive to the prospective consumer. Such pretreatment includes washing, peeling, dividing (dicing, slicing) and blanching.

An inconvenience arising when treating the food products with water is that a certain quantity of water adheres to/is taken up by the product under the action of adhesive or capillary forces. When refrigerating the food products, this leads to other inconveniences, of which only a few will be mentioned here. The comparatively high water content results in that the products, e.g. diced beefsteak tomatoes, form large lumps when refrigerated, which has a negative effect, inter alia on the time the product must be kept in the freezer, which means that the capacity of the freezer is reduced. Further, these lumped- together products pose a problem when they are packed after refrigeration, in that each package must contain a given volume or weight of the food product. In addition, the quality is adversely affected, especially when the product has a high tendency to take up water. The rela¬ tively large quantities of water accompanying the products into the freezer also result in considerable amounts of frost forming on the cooling battery of the freezer, which reduces the efficiency of the freezer and necessitates defrosting at short intervals.

These inconveniences are well-known in the art which embraces several suggested amendments. NO-B-156,771 discloses a method for producing concen¬ trated, refrigerated mashed potatoes, whereby bits of potatoes are dewatered in a net shaker after blanching and cooling. DE-OS-1,492,548 discloses another method comprising drying and precooling of composite berries, such as rasp¬ berries and blackberries (the Rubus family), prior to quick-freezing. The aim of the drying operation is not only to make the separate parts of the berries keep to- gether during refrigeration (the formation of ice crystals between the separate parts of the berries otherwise leading to the destruction, i.e. breaking, of the threads keeping these parts together, so that the berries fall apart when thawed), but also to achieve a cooling effect. Drying is carried out by leading air or dry nitrogen gas past the berries which thus are cooled. However, none of the above prior art methods corresponds to the require¬ ments of the food industry on modern refrigerating equip¬ ment; nor is any apparatus suggested. To meet market requirements, the food industry must be able to refrigerate the most diverse food products, e.g. peeled shrimps, sliced carrots, diced beefsteak tomatoes, and asparagus. Further, it should be possible to refrigerate the different products by the piece, which calls for advanced refrigerating and peripheral equipment. One object of the present invention is, therefore, to provide a method which, before refrigeration of food products, removes at least that water which, under the action of adhesive forces, adheres to the product after washing, blanching, etc. (in the following referred to as excess water).

Another object of the invention is to provide an apparatus for implementing this method.

A further object of the invention is to achieve a substantially even distribution, adapted to the feeding means of a freezer, of the dewatered products which are fed to the freezer for refrigeration, thereby to ensure both efficient use of the freezer capacity and refri¬ geration by the piece of the products when these are widely spaced apart.

Further, the dewatering effect of the inventive appa- ratus should be adjustable in such a manner that, in addi¬ tion to excess water, also water bound in the product can be removed, a certain drying effect being thus achieved. It is of considerable importance that the inventive dewatering apparatus be cost-effective, i.e. that it de- waters a number of products per time unit corresponding to the capacity of the freezer connected thereto.

Since it is necessary that the inventive dewatering apparatus functions together with different types of freezers, the apparatus must be compact and easily adap - able to an existing freezer.

These and other objects are achieved by a method for dewatering food products forming a product bed, wherein the food products are fed to a first dewatering zone, in which the food products are shaken to remove a first quan- tity of water, to be subsequently fed to a second dewater¬ ing zone, in which a gas is passed through the product bed to remove a second quantity of water, said method being characterised by the steps of passing the gas through the product bed from below, and imparting to the gas in the second dewatering zone such a velocity that the products in this zone are fluidised, as well as evenly distributed. To achieve the above objects and implement the inven¬ tive method, the invention further concerns an apparatus for dewatering food products forming a product bed, co - prising a product-shaking table arranged at an inlet end and forming a first dewatering zone, and a perforated bottom arranged adjacent to the shaking table and forming, together with a fan arranged below said bottom, a second dewatering zone, said bottom carrying the food products and said fan causing a gas to pass through the bottom and the product bed formed thereon, said apparatus being characterised in that a means is arranged in vertically adjustable manner transversely of the product bed adjacent to the second dewatering zone to form a fluidisation zone, and that the fan generates such a gas flow passing from below through the fluidisation zone and the product bed that the products in this zone are fluidised, as well as evenly distributed.

Further distinctive features of the invention are re¬ cited in the appended subclaims.

A preferred embodiment of the inventive apparatus will be described in more detail below, reference being had to the accompanying drawings, in which

Fig. 1 is a side view of an inventive apparatus for dewatering food products,

Fig. 2 is a front view of the apparatus in Fig. 1, Fig. 3 is a top view of the apparatus in Figs 1 and 2, but without the hood 58 which has been left out for reasons of clarity, and

Fig. 4 illustrates a placement of a spreading means arranged at a discharge nose of the inventive apparatus. Figs 1-3 show an inventive apparatus 2 for dewatering food products. The apparatus 2 is arranged as a treatment step between, for instance, a blancher and a freezer. In Figs 1 and 3, such a freezer is indicated by the presence of a heat-insulated wall 4 having an inlet opening 6. The inventive apparatus comprises a first and a second dewatering zone, designated A and B, respectively, in Fig. 3.

The first dewatering zone A is arranged at an inlet end 8 of the apparatus 2 which by some suitable means, such as a conveyor, is connected to e.g. a blancher. The first dewatering zone A is composed of a plurality (in this case three) of water-permeable bottoms 10, 12, 14 which are stepwise arranged and each of which extends between the elongate side walls 16, 18 of the apparatus transversely of the feeding direction of the products, illustrated by an arrow C in Fig. 3. As is apparent from Fig. 1, the bottoms 10, 12, 14, which are illustrated by dashed lines, are disposed at a distance below the upper edges 22 and 24 of the side wall 16 (and naturally also of the side wall 18) and an end wall 20, respectively. The bottom 10 connecting with the inlet end 8 is disposed uppermost. Each bottom 10, 12, 14 preferably consists of a grating or the like. At the end facing away from the end wall 20, the bottom 10 passes into a downwardly extending wall 28, the bottom 10 pro- jecting over the wall 28 in such a manner that a drop is formed from the bottom 10 to the subsequent bottom 12. Also the bottom 12 passes at one end into a downwardly extending wall 32, similar to the wall 28, the bottom 12 projecting over the wall 32. To clean the first dewatering zone A comprising the bottoms 10, 12, 14 on which scraps of products have accumulated, the lowermost bottom 14 is equipped with a drain gate 34. The bottom 14 is arranged at a distance above a perforated bottom 36 (see Fig. 3) forming part of the second dewatering zone B adjacent to the first dewatering zone A.

At the inlet end 8 of the apparatus, a product-flow divider 38 is arranged above the first bottom 10 and serves to divide the incoming product flow into several part flows. For example, and in the embodiment described, the divider 38 comprises three approximately semicylind- rical elements, of which the first element 40 is in centred manner fixed to the end wall 20 between the side walls 16, 18. The second and third elements 42 and 44 are preferably movably arranged transversely of the feeding direction of the product flow below the first element 40 in such a manner that the product flow is divided by the upwardly facing convex surface of the first element to drop, respectively, onto and obliquely below an upwardly facing convex envelope surface of the first element 40, and is thus further divided. Beneath the bottoms 10, 12, 14, a bottom wall 46 (see Fig. 1) connected to the side walls 16, 18 and the end wall 20 forms, together with a substantially vertical end wall 48 partly defining the first dewatering zone A, a funnel which, at the lower end, passes into a discharge pipe 50 for removing the excess water shaken off, parts of products, etc., that pass through the gratings and/or the drain gate.

As mentioned above, the second dewatering zone B com- prises a perforated bottom 36, which also is defined by the side walls 16, 18 and an apertured bottom wall 52 dis¬ posed at a distance above said funnel and connecting with the end wall 48. With the bottom wall 52 connects a fan duct 54 (see especially Fig. 2) through which a gas, pre- ferably air, is made to pass through the perforated bottom 36 from below by means of a fan 56. At the top, the second dewatering zone B is defined by a substantially semi- cylindrical hood 58 having elongate lower edges extending substantially in accordance with the upper edges 22 of the side walls. To facilitate cleaning and other maintenance work, the hood 58 opens on hinges 60 at one elongate lower edge. In Fig. 2, the open position of the hood 58 is indi¬ cated by dashed lines. In Fig. 3, the hood 58 has been omitted for reasons of clarity. In the longitudinal direction of the apparatus, the hood 58 has an extension exceeding the length of the second dewatering zone B, for reasons to be explained below. The short ends 62, 64 of the hood 58 have nets 66, 68 filtering the air that has passed through the perforat- ed bottom 36 and the product bed, and leaves the apparatus via the netted short ends 62, 64 of the hood. A weir 71 disposed transversely of the product flow C is arranged at the end of the dewatering zone B facing away from the inlet end 8. The weir 71 is preferably arranged in verti- cally adjustable manner above the perforated bottom 36, and is generally lowered to form the fluidisation zone and to distribute the products "flowing" over the weir 71 as products are fed in.

In the feeding direction C of the products, the second dewatering zone B passes into a feeding zone 70, which also is laterally defined by the side walls 16, 18, which end at the end 72 of the feeding zone facing away from the inlet end 8, and at the bottom is defined by a bottom wall 74 connected to the bottom wall 52. The end 72 is connected to a movable, heated discharge nose 76 which is introduced in the inlet opening 6 of e.g. a freezer and whose dimensions and inclination relative to the horizon¬ tal plane are adapted to the freezer at issue.

The side walls 16, 18, the bottom walls 46, 52, 74 and the end walls 20, 48 form a trough which is counter- balanced and supported by spring elements 82, 84 (Fig. 2 also shows a spring element 86) anchored in standards 78, 80 (of which only two are shown in Fig. 1). A vibrator 26 is attached to the trough. The hood 58 is supported by a frame 88 (see Fig. 2). Fig. 4 illustrates the discharge nose 76 on a larger scale. In this embodiment, a spreading means 92 is movably attached to the discharge nose. The spreading means 92 is here made up of a plurality of parallel, juxtaposed rods 94 (of which only one is shown in Fig. 4) of a suitable plastic material. The rod 94 is supported by a rotatable attachment 98 arranged at the discharge nose 76. The attachment 98 is so designed that the rod 94 can be dis¬ placed in the longitudinal direction.

The positions of the attachment 98 and the rods 94 are adjusted according to the product at issue, the free end 102 of the rod 94 performing, after the apparatus has been started, an upward-downward pivotal movement of com¬ paratively large amplitude, caused by the vibrations of the apparatus. The displacement of the rod 94 in the attachment 98 makes it possible to find the natural frequency of the rod 94 and adapt the amplitude to the product to be finely divided. It should here be pointed out that the placement of the spreading means described herein and shown in Fig. 4 is but an example, and that a further spreading means 92' may be arranged at the long side of the bottom 14 (see Fig. 1). The present invention can be used between e.g. a blancher and a freezer.

The moist products or parts thereof are fed, e.g. by a conveyor (not shown), to the inlet end 8 of the dewa¬ tering apparatus. The hood 58 is closed, and the vibrator 26 is activated, so that the entire trough vibrates.

The products drop onto the divider 38 dividing the product flow into a plurality of part flows. Depending on the product at issue, the second and third elements 42, 44 are laterally displaced to produce suitable part flows. Thus, a first distribution of the products in the appara¬ tus is achieved. The products drop onto the first grating bottom 10 and are moved in the direction of the arrow C by the vibrations generated by the vibrator 26. The products are shaken, and drop during feeding onto the grating bottom 12 or 14. The products are turned over several times, and excess water as well as some loose parts of products, such as peelings and pulp, drop to the lowest part of the trough formed as a funnel and ending in the discharge pipe 50. Depending on the product at issue, this waste can be used for making juice.

After most of the excess water has been removed in the first dewatering zone A, the products are conducted, preferably via the spreading means 92' arranged at the long side of the bottom 14, into the second dewatering zone B. Owing to the spreading means 92', the products are finely divided when entering the second dewatering zone B.

Via the duct 54, the high-capacity fan 56 blows air from below through the holes in the perforated bottom 36 and causes fluidisation of the products in this zone. The relatively large distance between the fluidised products in this zone leads to an effective dewatering of the products, the air passing the products taking up the water. Since much of the excess water is shaken off mechanically, the degree of dewatering in the second dewatering zone B can be controlled by adjusting the air flow through the product bed. If desired, also a certain amount of the bound water can be removed, which may advan¬ tageously affect the product quality.

The humid air is intercepted, and the water in the air condenses on the inner surface of the hood 58 to flow down to a drain 90 arranged at the lower edge of the hood. Any product parts entrained by the air, such as peelings and pips, are effectively intercepted by the nets 66 and 68 which are arranged at the short ends 62, 64, respec¬ tively, of the hood and through which the air passes out into the surroundings. The air is so clean that in most cases no further treatment will be needed. It will be appreciated that the hood must cover at least the second dewatering zone B in order to intercept the humid air. Preferably, the hood 58 covers a surface larger than that of the perforated bottom 36 to ensure that the humid air containing peelings, pips etc. is actually intercepted and the water condensed.

The fluidising air flow in the second zone B not only produces dewatering and has a certain cleaning effect on the products; it also contributes to an even distribution of the products across the entire width of the apparatus. Owing to different spreading means, the products are thus evenly fed out via the discharge nose 76, so that the capacity of the freezer can be optimally used. There are, however, products which are extremely difficult from a refrigeration-technical point of view, such as diced onions and sliced products e.g. zucchini, requiring the use of the spreading means 92 shown in Fig. 4 to con¬ tribute, as a last step, to effectively distributing these products when entering the freezer. When nonfluidisable products are to be dewatered, or when the fluidisation effect cannot be used, the weir 71 may, if need be, be raised to open the passage, so that the products thus do not flow over the weir 71. Owing to the effective de¬ watering, the formation of frost on the cooling battery of the freezer initially mentioned is reduced, and the freezer need thus not be serviced/defrosted as often as before. Further, it also makes it possible to increase the degree of freezing by piece of e.g. sliced products while maintaining their taste and appearance.

When the hood 58 is raised, the apparatus proper can be easily and expediently cleaned by flushing, not least owing to the drain gate arranged in the first dewatering zone A.

Thus, the inventive apparatus very effectively dewa- ters food products. In a first step, the main part of the water adhering to the products is removed (the excess water), it being possible to further adjust the water content by means of the air velocity and the time of stay for the products in a second step. Owing to the fluidi¬ sation of the products in the second step, one obtains a very effective dewatering (and cleaning to a certain extent) and an even distribution of the products across the entire width of the apparatus.

It goes without saying that the above embodiment and the suggested use thereof as a treatment step between a blancher and a freezer are but examples, and that the expert may devise other means, modifications and areas of use. All such alterations and modifications falling within the scope of the inventive idea are to be regarded as embraced by the appended claims.

Claims

1. A method for dewatering food products forming a product bed, wherein the food products are fed to a first dewatering zone (A), in which the food products are shaken to remove a first quantity of water, to be subsequently fed to a second dewatering zone (B), in which a gas is passed through the product bed to remove a second quantity of water, c h a r a c t e r i s e d by the steps of passing the gas through the product bed from below, and imparting to the gas in the second dewatering zone (B) such a velocity that the products in this zone (B) are fluidised, as well as evenly distributed.

2. The method of claim 1, c h a r a c t e r i s e d by the steps of causing the water taken up by the gas in the second dewatering zone (B) to condense on an inner surface of a hood (58) arranged above this zone (B), and conducting said water to a drain (90).

3. The method of claim 2, c h a r a c t e r i s e d by the steps of arranging, at an inlet end (8), a product- flow divider (38) for distributing the products in said first dewatering zone (A), and arranging, transversely of the feeding direction (C) of the products, a means (92, 92' ) for finely dividing said products.

4. An apparatus for dewatering food products forming a product bed, comprising a product-shaking table arranged at an inlet end (8) and forming a first dewatering zone (A), and a perforated bottom (36) arranged adjacent to the shaking table and forming, together with a fan (56) arranged below said bottom (36), a second dewatering zone (B), said bottom (36) carrying the food products and said fan (56) causing a gas to pass through the bottom (36) and the product bed formed thereon, c h a r a c t e r i s - e d in that a means (71) is arranged in vertically adjustable manner transversely of the product bed adjacent to the second dewatering zone (B) to form a fluidisation zone, and that the fan (56) generates such a gas flow passing from below through the fluidisation zone and the product bed that the products in this zone (B) are fluid¬ ised, as well as evenly distributed.

5. The apparatus of claim 4, c h a r a c t e r ¬ i s e d in that the shaking table arranged at the inlet end (8), the perforated bottom (36), and an outlet zone (70) adjacent to the second dewatering zone (B) are arranged in a common trough having side walls (16, 18), bottom walls (46, 52, 74) and end walls (20, 48) and being resiliently mounted on standards (78, 80), and that a vibrator (26) fixed to said trough causes the latter to vibrate, the products being fed from the inlet end (8) to an outlet end (76).

6. The apparatus of claim 4 or 5, c h a r a c ¬ t e r i s e d in that the shaking table comprises water- permeable bottoms (10, 12, 14) which are stepwise arranged, the uppermost bottom (10) being arranged at the inlet end (8).

7. The apparatus of claim 6, c h a r a c t e r i s ¬ e d in that the lowermost bottom (14) at one long side facing away from the inlet end (8) is equipped with an openable drain gate (34) adapted to facilitate cleaning of the bottoms (10, 12, 14).

8. The apparatus of claim 6 or 7, c h a r a c ¬ t e r i s e d by a product-flow divider (38) arranged at the inlet end (8) above the uppermost bottom (10).

9. The apparatus of claim 8, c h a r a c t e r i s ¬ e d in that the product-flow divider (38) comprises a first convex element (40) which in centred manner is fixed to the end wall (20) of the inlet end (8), and two convex elements (42, 44) which are movable transversely of the feeding direction (C) of the products and arranged late¬ rally obliquely below the first element (40), said ele- ments (40, 42, 44) facing the inlet end (8).

10. The apparatus of any one of claims 4-9, c h a r a c t e r i s e d by a hood (58) arranged above the second dewatering zone (B) and having netted short sides (62, 64), the nets (66, 68) serving to filter the gas intercepted by the hood, the water in the gas condens¬ ing on the inner surface of the hood and being conducted to a drain (90).

11. The apparatus of any one of claims 4-10, c h a r a c t e r i s e d by a spreading means (92, 92' ) movably arranged transversely of the feeding direction (C) of the products and consisting of a plurality of parallel, juxtaposed rods (94).

12. The apparatus of claim 11, c h a r a c t e r - i s e d in that each rod (94) in its longitudinal direc¬ tion is adjustably supported by an attachment (98) and is made of a suitable plastic material.