WO1997004665A1

WO1997004665A1 - Surface moisture removal from food products

Info

Publication number: WO1997004665A1
Application number: PCT/AU1996/000480
Authority: WO
Inventors: Clement Victor Braha; David Keith Ward; David Leslie Furby
Original assignee: Alta Spinner Australia Pty. Limited
Priority date: 1995-07-31
Filing date: 1996-07-30
Publication date: 1997-02-13

Abstract

Wet potato slices are processed to remove surface moisture prior to a frying operation by feeding a quantity of the slices into a cylindrical drum having a perforated side wall, an inlet opening at the top and a closable discharge door at the bottom. Spinning of the drum at about 1000 rpm for about 20 seconds produces a low residual surface moisture content and at a discharge station the door is opened to discharge the processed potato slices into a frying unit. At the discharge station the perforated drum is preferably braked to a standstill to facilitate discharge. A preferred embodiment uses about 7 such drums mounted around a turntable which sequentially moves the drums from a loading station, through a spinning zone and to a discharge station so that a semi-continuous method is provided.

Description

SURFACE MOISTURE REMOVAL FROM FOOD PRODUCTS

The present invention concerns improvements and developments relating to surface moisture removal from food products, and more particularly can be applied to methods and apparatus for processing food products in a manner to remove surface moisture. For example, the invention can be applied to processing potato slices or other cut fragments for the production of potato chips, which are sometimes known as potato crisps. Although the invention is described with particular reference to the processing of potato slices, the invention also extends to and is applicable to analogous processes and apparatus for removal of liquid phase components of various materials and especially those which are analogous in form and character to potato slices.

Commercial plants for processing and packaging of potato chips are usually designed for large-scale, essentially continuous production. A typical plant will be arranged to process 4,000 kg of potato slices per hour and the output will have a weight of around 1,000 kg per hour. The plant is arranged to receive, peel, slice and wash potato slices which are then advanced to a deep frying process which rapidly process the potato slices into the final potato crisp product, which is bagged and packaged at the end of the production line. Typically the washed potato slices will have surface moisture accounting for about 10% of the weight of the potato slice and this is in addition to the moisture retained within the potato structure. It has long been understood that surface moisture on potato slices is deleterious to the frying process and the quality of the final product. Therefore efforts have been made to remove as much surface moisture as possible in a high speed process, which must not subject the relatively fragile potato slices to damage.

It is well known to use an air knife type of apparatus or air blast apparatus to sweep some of the surface moisture off the potato slices. One known apparatus is marketed by Heat & Control, Inc of San Francisco, USA and others and relies upon the potato slices being advanced along a stainless steel mesh conveyor and subjected to an air blast. However, experience shows that this system does not achieve removal of a high proportion of the surface moisture, as would be desired. Typically surface water accounts for 9-10% by weight of washed potato slices and only a minor proportion of the surface water is removed with the known techniques so that 7% or more of the mass of potato slices entering the fryer is surface moisture.

Accordingly there has been a longstanding unfulfilled need for practical, cost effective and efficient removal of surface moisture and capable of coping with high volume commercial processing line. According to a first aspect of the present invention, there is provided a method of removing liquid from a feedstock comprising a mass of solid elements and a liquid, the method comprising discharging feedstock downwardly through an upper inlet port into a cylindrical vessel having a perforated peripheral wall, subjecting the vessel to rotation about its axis at a selected speed and for a selected time such that deleterious effects on the solid elements are substantially avoided and under centrifugal force liquid migrates from the surface of the solid elements out through the perforated wall to be discharged, and opening a discharge port at the opposite end of the vessel to the inlet port for discharging the feedstock.

An important form of the invention relates to producing potato chips; in this form broadly the invention consists of a method of producing potato chips comprising preparing potato slices in a preliminary stage which produces washed slices having surface water, supplying the washed potato slices to a centrifugal water removal apparatus, operating the water removal apparatus at a selected speed to remove the majority of the surface water substantially without deleterious mechanical damage to the potato slices, and discharging the potato slices to a potato frying station.

In this specification the reference to "potato fragments" includes slices or other shaped portions. Use of the word "comprising" is to specify a non- exhaustive list of components.

Preferably the process is operated by disposing the cylindrical vessel with a substantially vertical axis and loading the feedstock through an inlet port which is uppermost while the vessel is rotated at processing speed, the vessel being at least substantially slowed down for the purpose of discharge of feedstock when a discharge door at the lower end of the vessel is opened.

The discharge door preferably comprises a rotatably mounted disk, a support structure for the disk and a control system for moving the support structure to displace the disk into engagement with the rotatable vessel, whereby the disk rotates with the vessel.

In a preferred embodiment, the support structure includes a pivotal mounting so that for discharging feedstock the door structure is swung downwardly to an acute angle.

In a preferred process the vessel is rotated at approximately 1000 rpm and preferably at about 940 rpm. In one embodiment a drive motor is mounted on the lower side of the discharge door in direct engagement with the rotatably mounted disk of the discharge door, the disk being adapted to engage with a lower portion of the cylindrical vessel and thereby transmit motion to it. However, with a view to reducing the overall vertical height of the apparatus as well as providing a practical engineering solution, the applicants alternatively propose a variation where an electric motor for rotatably driving discharge door and thus the cylindrical vessel is mounted on an upper side region of the apparatus, e.g. on the outside of a peripheral drum which enshrouds the rotatable cylindrical vessel. A drive belt system can be used to engage and drive the door. Particularly for this embodiment preferably the door is adapted to be opened by actuation of a double acting hydraulic ram which moves the door downwardly and a secondary mechanism is then provided, e.g. for a secondary ram to displace the door laterally either by pivotal motion in a horizontal plane or straight lateral motion in a horizontal plane.

Most preferably the rotatable disk has a frusto¬ conical form whereby its periphery tapers inwardly in an upward direction to engage at corresponding or similar taper on the lowermost portion of the cylindrical vessel whereby the closing action applies an interference fit.

Advantageously opening and closing of the door is controlled by a pneumatic or hydraulic actuator. It has now been found that a surprisingly compact design can successfully process a high through put of product. For example when potato slices for potato chip manufacture are being handled and when the machine is the preferred embodiment having seven parallel drums operating in sequence, each drum needs to be only about

650mm in high and about 340mm diameter whereby the whole machine can process about 14,000 kg of moist potato slices per hour, thereby discharging about 13,300 kg of finished slices whereby most of the surface moisture has been removed. About 2800 kg of finished crisps result.

Particularly for the purpose of processing potato slices for potato chips, an apparatus that can function in the middle of a continuous processing line is required and the apparatus must be capable of being accommodated in a compact form and must operate with very high efficiency to minimise surface moisture on the potato slices without damage to the slices.

For this purpose a preferred embodiment of apparatus is used and comprises a multiplicity of independently rotatable cylindrical perforated vessels or drums spaced around a turntable and rotatable about their respective vertical axes, each drum being of the form described above for practising the method. The process can be operated by step-wise rotation of the turntable to advance each drum in turn through a succession of stations at which the turntable stops for a short time for loading and discharge. However, it is considered preferable to provide a configuration of chutes for loading potato slices into the respective drums and also to provide an appropriate discharge chute and configuration so that continuous operation of the turntable is achieved. Thus, loading happens while a drum transits a loading station and similarly discharge occurs at a discharge station speedily and in between is a zone in which the drums spin typically at about 1000 rpm and typically for 20 seconds in order to remove surface moisture to a low level. Preferably, the invention is implemented with seven perforated drums provided on a turntable with a drum resident in a loading zone and a discharge zone for about 4 seconds and in a spinning zone for around 20 seconds.

Another aspect of the invention consists in apparatus for practising the process described above in any one of its forms.

In a further aspect, the invention consists in a potato chip making process comprising supplying washed potato slices to a centrifugal water removal apparatus, operating the water removal apparatus at a selected speed to remove the majority of the εurface water substantially without deleterious mechanical damage to the potato slices, and advancing the processed potato slices to a frying station. Preferably the centrifugal water removing apparatus is operated at a speed of around 1000 rpm (e.g. 940 rpm) for a moderate length of time of say around 20 seconds whereby relatively gentle handling of the potato slices is achieved yet a commercially acceptable rate of processing is achievable to integrate the process into a commercial potato chip manufacturing process.

Preferably, the centrifugal water removal step uses a multi-centrifugal apparatus comprising vertical tubes which are top loaded and having bottom discharge doors, each tube being braked when the door is opened to discharge potato slices.

Advantages which can flow from use of the present invention include:

(a) Surface moisture is removed efficiently to a great extent (e.g. 0.8% by weight) ; this reduces the disadvantages of significant moisture present with the slices. Moisture has to be converted to steam in the frying process and there is an energy cost. The presence of more than a trace of surface moisture has significant impact in deleteriously reducing the frying oil temperature thereby slowing down the cooking process. This would result in disadvantageous absorption of oil into the structure of the chip, reducing the quality of the chip and increasing processing time.

(b) Surface moisture causes a significant increase in the amount of oil driven off in vapour form, which is a loss to the system, potential pollution and an expense.

(c) Presence of surface moisture significantly increases energy consumption.

(d) Longer cooking times affects quality of the chip and potential shelf life. It is estimated that at least preferred embodiments of the invention can provide washed potato slices supplied to a fryer with only 2-3% and possibly as low as 0.8% by weight of the mass being surface moisture, yet high output rates (e.g. greater than 13,000 kg/hr) can be achieved.

For illustrative purposes only an embodiment of centrifugal drying apparatus suitable for processing potato slices or potato chips (crisps) is described with reference to the drawings of which:

Figure 1 is a schematic general arrangement in side view of an apparatus in a potato chip processing line; Figure 2 is a schematic plan view of the seven- station centrifugal processing apparatus of Figure 1;

Figure 3 is a schematic front elevation of part of the apparatus of Figure 1 illustrating one centrifugal cylinder with its lower discharge door in a closed position, the open portion being shown in dotted lines; and

Figure 4 is a plan view showing an alternative funnel design for loading potato slices without stopping the turntable. Figure 1 shows a centrifugal drying apparatus 10 arranged to receive potato slices from a washer 11 via a supply elevator 12 in batches and to discharge dried slices into a discharge shute 13, which feeds the slices into a continuous tunnel-type fryer 14. The general scheme of the apparatus shown on the drawings is that washed potato slices are supplied from a continuous known processing machine which peels, slices and washes potatoes typically at a rate of around 4,000 kg/hour, although some commercial production lines may need to be designed to operate at substantially higher rates. The washer 11 supplies slices via a conveyor 12A (Figure 2) to the elevator 12.

The present embodiment has seven upright cylindrical perforated baskets 15, which are moved through a series of seven stations. The embodiment of Figures 1 to 3 was designed so that the baskets 15 move sequentially and intermittently through the series of stations although in another embodiment, described below, a continuous motion can be provided. At a first station A (see Figure 2) approximately 14 kg or more of potato slices are discharged as a batch from the supply elevator into a funnel 20 which leads to an open top of a cylindrical basket, while the basket is rotating at a speed of about 940 rpm. This filling step is conducted within 3 seconds and then a turntable mechanism is actuated to rotate the drying apparatus in about 1 second through approximately 51.4° to move each basket to its next station. Each basket at stations A, B, C, D and E is continuously rotated to cause centrifugal drying of the potato slices, but when a basket reaches the sixth station F a bottom discharge door 16 is opened and the speed reduced by a brake mechanism whereby discharge commences and the product is discharged into the discharge shute 13 which leads to the commercial potato fryer 14.

The supply elevator 12 comprises an upwardly inclined conveyor having flights, which take up potato slices emerging from a conventional peeler/slicer/washer unit 11. The elevator has a drive mechanism controlled in synchronisation with the drying apparatus so that the desired quantity of potato slices are supplied to a basket at position A and during the short transition time when the turntable is operated to move baskets from station to station it would be possible to operate the elevator 12 continuously, at least providing a discharge spout 19 can reliably direct the potato slices into the basket leaving station A and then into the basket 15 arriving from station G to station A. If necessary a synchronised swivel mechanism to oscillate the spout could be incorporated in order to direct correctly slices into one basket or the other or alternatively a brief interruption in drive to the elevator might be provided to ensure potato slices are not spilt outside the receiving baskets 15.

Figure 3 shows in enlarged sectional detail one of the cylindrical baskets mounted on a centre support drum 17. The centre support drum 17 is mounted via a bearing 60 on a support 61 which permits the apparatus itself to be supported on a platform 21 (shown in Figure 1) . The bearing unit 60 includes roller bearings 62. The centre support drum 17 has an annular base 63 to which is fixed a ring-shaped bottom plate for mounting each drum unit. Each drum unit includes a rotatable basket 15 rotatably mounted on the periphery of the centre support drum 17 by respective top plates 64 and bottom plates 65.

A turntable unit is thus provided by the centre support drums 17 to move sequentially the baskets 15 from station to station. A drive motor (not shown) is provided for rotating the turntable unit in response to a control unit which is programmed to operate intermittently to achieve the method of operation described above.

Associated with each basket 15 is a cylindrical shroud 30 fixed between the top and bottom plates. Within the each shroud a perforated stainless steel cylindrical basket 15 is mounted. Typically the cylindrical basket is 340mm diameter and the outer shroud is 400mm diameter and in use water migrates radially outwardly into the space and is discharged through an annular drain 66 at the bottom of the apparatus.

The discharge door 16 is pivotally mounted through a hinge 45 to the radially outward portion of the bottom plate 65, the door having an integral arm 46 extending radially outwardly to a further pivotal linkage 47 connected to the operating ram 48 of a pneumatic cylinder 49, the top end of which is pivotally mounted through a mounting 49 to the top plate 64. An electrical drive motor 35 is mounted to the base of the discharge door 16 and has its drive shaft permanently connected to a rotatable drive plate 50 having a frusto-conical form tapering upwardly and, as shown in Figure 3, adapted to be a taper fit into the bottom end of the cylindrical basket 15. The upper end of the cylindrical basket 15 has a neck 51 rotatably mounted in a bearing 52 whereby the whole drum is supported through a top drum support structure 53. This support structure is removable to facilitate servicing.

An additional feature provided is a polyurethane mat or cover for the drive plate 50 which is designed as a wear component and also a component which can be readily removed for cleaning.

At station F shown in Figure 2, the discharge door is opened by actuating the pneumatic cylinder 49, the door swinging down to the position shown partially in dotted lines in Figure 3 thereby permitting discharge of the dried potato slices.

Figure 1 shows an optional additional feature, namely, a water spray head 22 provided for discharging a spray of water for a few seconds during loading of potato slices into a cylindrical drum. This has been found to be especially beneficial in facilitating relative movement of slices as they pack into the drum whereby the resultant product has lower residual moisture than would otherwise be the case, especially when the slices are relatively thin.

Another embodiment of the invention is one in which the turntable structure is adapted to be driven continuously. To facilitate this, an alternative funnel structure as shown in Figure 4 is provided on the top of each cylindrical vessel. In this case in plan view the funnel has a periphery of trapezoidal shape 23 leading to a downwardly projected cylindrical central discharge spout 24 leading into the top of a cylindrical vessel . The funnels overlap and thus provide a continuum around the apparatus for collecting all discharged potato slices .

Experiments using a prototype apparatus embodying the invention have demonstrated that very low residual surface moisture levels are experienced and values as low as 0.8% by weight have been achieved. Consequent to this processing technique it has been found that considerable cost savings are achieved in the frying step by avoiding oil pickup onto the potato chips and avoiding loss of oil with steam (which is discharged) ; there is also a corresponding reduction in fuel required to maintain the desired cooking temperature. Oil pickup of less than 30% in the final potato chips has been experienced whereas typically with prior art processes the total weight of product comprising cooking oil is 36%. Better quality chips which are believed to have a better shelf life are produced and there is less oil in the final product and consequentially when sold by weight there is more potato.

An important advantage found with these preferred embodiments of the invention is that the handling of the potato slices greatly reduces wastage. With conventional processes as much as 20% by weight of potato slices are lost to the final packaging process due to fragmentation resulting in fine particles or portions which have to be dumped. By contrast, experiments with embodiments of the present invention show that wastage due to fines is as low as 5-6% based on the weight of the potato.

Preferably a water spray is used from spray head 22 as described above with reference to Figure 1. Apart from aiding the packing of potato slices so that effective moisture removal occurs under centrifugal force, this has been found to solve another problem. The slicing process for producing potato slices does damage or bruise some cells in the potato structure thereby releasing starch which tends to settle in the wash tank but an appreciable quantity of starch becomes distributed over and sticks to the slices. After the frying process this results in an adverse blotchy appearance to the potato slices. The water spray has been found to aid removal of starch in the processing according to the present invention and this enhances the appearance of the product .

Claims

THE CLAIMS :

1. A method of removing liquid from a feedstock comprising a mass of solid elements and a liquid, the method comprising discharging feedstock downwardly through an upper inlet port into a cylindrical vessel having a perforated peripheral wall, subjecting the vessel to rotation about its axis at a selected speed and for a selected time such that deleterious effects on the solid elements are substantially avoided and under centrifugal force liquid migrates from the surface of the solid elements out through the perforated wall to be discharged, and opening a discharge port at the opposite end of the vessel to the inlet port for discharging the feedstock.

2. A method as defined in claim 1 and wherein the method includes disposing the cylindrical vessel with a substantially vertical axis and loading the feedstock through the inlet port which is uppermost while the vessel is rotated at processing speed, and at least substantially slowing down the vessel during the discharging step when a discharge door at the lower end of the vessel is opened.

3. A method as defined in claim 2 and including providing and using the discharge door in a form which comprises rotatably mounted disk, a support structure for the disk and a control system for moving the support structure to displace the disk into engagement with the rotatable vessel, whereby the disk rotates with the vessel .

4. A method as defined in any one of the preceding claims and including rotating the vessel at a speed of about 1000 rpm for discharging liquid through the perforated wall .

5. A method as defined in any one of the above claims wherein the feedstock comprises washed potato fragments and wherein the vessel is rotated for a time of about 20 seconds to remove surface water.

6. A method of producing potato chips comprising preparing potato slices in a preliminary stage which produces washed slices having surface water, supplying the washed potato slices to a centrifugal water removal apparatus, operating the water removal apparatus at a selected speed to remove the majority of the surface water substantially without deleterious mechanical damage to the potato slices, and discharging the potato slices to a potato frying station.

7. A method as claimed in claim 6, and wherein the method uses a cylindrical vessel having a perforated wall arranged to be rotated about a vertical axis, an upper inlet port, a lower discharge port and a discharge door, the method including loading a quantity of wet potato slices through the inlet port, spinning the cylindrical vessel at a speed of the order of one thousand revolutions per minute (1000 rpm) , at least substantially slowing the cylindrical vessel after a substantial portion of surface water has been discharged through the perforated wall of the cylindrical vessel, and opening the discharge door to discharge the potato slices for frying.

8. A method as claimed in claim 7, and comprising using an apparatus wherein a multiplicity of similar cylindrical vessels respectively mounted to move in turn around a closed path having a loading station, a spinning station and a discharge station, each cylindrical vessel being adapted to contain about 20 kg of potato slices, and the method including loading wet potato slices into a cylindrical vessel while it is spinning, conducting spinning for about 20 seconds and then discharging the potato slices.

9. A method as claimed in claim 8, and further comprising applying a water spray to the potato slices during loading.

10. A method as claimed in claim 8 or claim 9, and including maintaining spinning of a cylindrical vessel for approximately five times the residue time occupied in the loading step.

11. An apparatus for removal of surface moisture from food product such as potato slices and comprising a cylindrical vessel having a perforated peripheral wall, an inlet port at the upper end, a discharge port at the lower end and a discharge door adapted normally to close the bottom end of the cylindrical vessel, mounting means for selectively rotating the cylindrical vessel about a vertical axis, moving means for moving the cylindrical vessel along a closed path comprising a loading station at which wet food product is adapted to be poured into the vessel; a station at which the vessel is rotated to cause surface moisture to migrate under centrifugal force through the perforated side wall of the cylindrical vessel and a discharge station at which a discharge door is adapted to be opened and the food product discharged under gravity.

12. An apparatus as claimed in claim 7, and wherein the discharge door has a rotatably mounted disk adapted to be driven and displaced into engagement within the cylindrical vessel to rotate the vessel.

13. An apparatus as defined in claim 12, wherein the rotatable disk has a frusto-conical form whereby its periphery tapers inwardly in an upward direction to engage at corresponding or similar taper on the lowermost portion of the cylindrical vessel .

14. An apparatus as claimed in any one of claims 11 to

13, and wherein the apparatus comprises a multiplicity of independently rotatable, cylindrical vessels spaced around a turntable and rotatable about their respective axes.

15. An apparatus as claimed in any one of claims 11 to

14, and further comprising control means for controlling the drive means and the moving means such that the cylindrical vessel is rotated at about 1000 rpm when being loaded, has a spinning time for around 20 seconds for removing surface moisture on the food product and is adapted to be braked to a standstill while the discharge door is opened for discharging the food product.

16. An apparatus as claimed in claim 14, wherein approximately seven cylindrical vessels are provided and the moving means for the turntable is adapted to be controlled to move the cylindrical vessel at a steady speed between the respective stations.