WO2012104215A1

WO2012104215A1 - Apparatus and method in the manufacture of low oil potato chips

Info

Publication number: WO2012104215A1
Application number: PCT/EP2012/051345
Authority: WO
Inventors: Michael Alfred James SPURR; Barbara Louise WARBURG; Paul Fredrick TOMLINSON
Original assignee: Frito-Lay Trading Company Gmbh
Priority date: 2011-01-31
Filing date: 2012-01-27
Publication date: 2012-08-09
Also published as: GB201101606D0; GB2481468B; GB2481468A

Abstract

An apparatus for separating potato slices in a supply of oil, the apparatus comprising a flume comprising a gulley having a flume inlet at an upstream inlet end and a downstream outlet end, a fishtail ramp having opposed lateral walls connected at an upstream end thereof to the downstream end, the fishtail ramp progressively increasing in width from the upstream end to a downstream end, and a discharge chute connected at an upstream end thereof to the fishtail ramp, and a pump connected by an outlet pipe to the upstream inlet end of the gulley for pumping a supply of oil containing a plurality of potato slices into the gulley.

Description

APPARATUS AND METHOD IN THE

MANUFACTURE OF LOW OIL POTATO CHIPS

This invention relates to an apparatus and method for separating potato slices in the manufacture of low oil potato chips.

It has been known for many years to produce potato chips from slices of potato which are fried in oil, usually vegetable oil. Typical conventional potato chips have an oil content of about 30 to 35 wt% oil, based on the total weight of the potato chip. Potato chips exhibit specific organoleptic properties, in combination with visual appearance, to the consumer. The consumer desirous of purchasing a potato chip has a clear expectation of these product attributes in the product.

There is a general desire among snack food manufacturers, consumers and regulatory authorities for healthier food products. In the snack food industry, this has led to a desire for lower fat products. However, even though there may be a general consumer awareness of the benefits of eating lower fat versions of, or alternatives to, existing snack food products, the consumer generally requires the product to have desirable attributes such as texture and flavour. Even if a snack food product is produced which has high nutritional attributes, unless it also has the texture and flavour required by the consumer, the product would not successfully provide the consumer with an acceptable product to replace previous, less healthy snack food products. The challenge among snack food manufacturers is to produce nutritional or more healthy foods which provide the consumer with an improved taste and sensation experience, or at the very least do not compromise on taste and sensation as compared to the consumer's expectation for the particular product or class of products purchased.

There are in the market so-called lower oil snack food products, including potato chips and other products. Some of these processes are produced by modified frying processes using different frying temperatures than those conventionally employed, or cooking processes other than frying, such as baking. Some of these products produce snack foods with low oil, even as low as 5wt%, but the snack food product is not regarded by the consumer to be an acceptable alternative to a potato chip, because the product cannot exhibit the organoleptic properties, in combination with the visual appearance, of a potato chip.

WO-A-2008/01 1489 and WO-A-2009/091674 in the name of Frito-Lay Trading Company GmbH disclose processes for making a healthy snack food. In those processes, a snack food is made so as to have an appearance and taste similar to conventional fried snack products, such as a potato chip. The potato slices are subjected to a sequence of steps which avoids frying of the slices in oil, and the result is a low fat potato chip.

In particular, these specifications disclose the use of microwave cooking of potato slices which have been preconditioned, for example by being treated in oil. Prior to the microwave cooking process, the potato slices are flexible, and have a typical thickness of 1 to 2.5 mm. The microwave cooking rapidly, or explosively, dehydrates the potato slices to achieve low moisture content in a drying step which simulates the conventional frying dehydration rate. The rapid microwave dehydration rigidifies the cooked potato slices, so that they have a crispness resembling that of typical fried potato chips. Additional final drying steps may be employed, for example using microwave drying.

It is disclosed that the oil preconditioning step comprises lipophilic preconditioning by placing the slices into a warm oil flume, a batch kettle or a continuous oil dip. During the lipophilic preconditioning step, a final slice temperature of about 60°C to about 99.9°C and a duration of about 30 to 600 seconds may be employed.

Subsequent to the lipophilic preconditioning step an oil removal step is employed. The oil removal step is disclosed as being performed using a variety of different wet methods, which may, for example, use at least one of the following: a steam blancher; a perforated rotating drum; washing in a hot or cold water bath; pressurised water jets; water knives; air knives; air atomised water nozzles; a mist of fine droplets of water; superheated steam or nitrogen; or centrifugal oil removal. It is disclosed that the most preferred embodiment uses a water spray comprising a mist of fine droplets of water.

After the oil removal, the slices are subjected to the microwave cooking described above. These prior specifications do not disclose a product transfer system between these various stations which can be used in a large scale commercial production process and provide effective and efficient implementation of the specific processing parameters of each step.

In particular, the slices may have been subjected to a bulk or batch treatment in the lipophilic pre-conditioning oil treatment step. In contrast, in subsequent process steps such as the oil-removal step and particularly the microwave cooking step, it is necessary for the potato slices to be separated into substantially single, independent non-overlapping slices. The slices need to be singulated as much as possible. Singulation reduces the number of potential weld points between slices that, during the microwave process, may cause arcing, uneven drying and welded or fused double slices or clumps of more than two slices in final potato chip product.

Also, for the next unit operation, such as the de-oiler or the microwave oven, it is necessary for the slices to be spread uniformly across the whole process width. Since the lipophilic pre-conditioning oil treatment step may be carried out as a bulk or batch treatment it may have a narrower process width than the process width of subsequent process steps which may have a larger process width since the same mass flow rate is applied to individually separated slices.

There is a need to be able to vary the process width of the potato slices while retaining a uniform product distribution across the downstream process width and additionally achieving a high proportion of independent separated non-overlapping singulated slices.

Arcing during microwave dehydration limits how much power can be transferred to the product and therefore the capacity of the microwave oven. Product overlap and mutual contact are major factors in causing undesired arcing during microwave dehydration.

Even though those prior patent specifications disclosed an effective lipophilic preconditioning step, and also subsequent processing steps, there is still a need for an apparatus and method which can reliably provide a desired product distribution of potato slices for processing steps downstream of the lipophilic pre-conditioning step of potato slices in oil when a large mass flow rate of potato slices, as used in large-scale commercial production of potato chips, is required to be treated.

During frying of conventional potato chips in a fryer, in which the potato slices are rapidly dehydrated and cooked in high temperature oil to provide the desired organoleptic properties, as the slices dehydrate the slices float individually to the surface of the oil. In addition to rapidly drying, the potato slices cook and harden, and such rigidification also helps to retain the chips substantially separate in the fryer. However, when lipophilically pre-conditioning the potato slices in oil at a lower temperature which does not cause dehydration of the potato slices, the slices remain dense and they tend to sink in the oil. The slices also do not rigidify but remain flexible. The slices therefore tend to form clumps of slices. Such clumps mean that the slices are not uniformly treated by the oil and they may not be capable of being processed in the later processing steps. Also, the clumps can form blockages in a continuous production line, making processing at a large scale production rate difficult.

There is a need for an apparatus and method which can incorporate both a lipophilic preconditioning step and downstream production steps such as de-oiling and microwave dehydration which can operate continuously at a commercial scale and can avoid the formation of clumps of potato slices which cannot readily be processed. There is also a need for producing individual single slices, in a continuous large-scale production apparatus and method, following a lipophilic preconditioning step which can otherwise tend to produce overlapped slices or clumps of slices.

Furthermore, there is still a general need to provide an oil content during the processing which ensures that the final non-fried potato chip has a lower oil content as compared to conventional fried potato chips yet has a consumer acceptance, provided by the resultant flavour and organoleptic properties, on parity with conventional fried potato chips.

There is accordingly still a need for an apparatus and method for efficiently and reliably manufacturing, in a cost effective manner, a low fat potato chip which has not been fried but has organoleptic properties, in combination with the visual appearance, of a conventional fried potato chip. The present invention accordingly provides an apparatus for separating potato slices in a supply of oil, the apparatus comprising a flume comprising a gulley having a flume inlet at an upstream inlet end and a downstream outlet end, a fishtail ramp having opposed lateral walls connected at an upstream end thereof to the downstream end, the fishtail ramp progressively increasing in width from the upstream end to a downstream end, and a discharge chute connected at an upstream end thereof to the fishtail ramp, and a pump connected by an outlet pipe to the upstream inlet end of the gulley for pumping a supply of oil containing a plurality of potato slices into the gulley.

The present invention further provides a method of separating potato slices in a supply of oil, the method comprising the steps of:

(a) pumping a supply of oil containing potato slices into a gulley of a flume device;

(b) flowing the potato slices in the oil from a downstream end of the gulley into a downwardly inclined fishtail ramp of the flume device, the fishtail ramp having opposed lateral walls and progressively increasing in width from an upstream end to a downstream end of the fishtail ramp, the downwardly flowing potato slices progressively spreading across the width of the fishtail ramp; and

(c) discharging the potato slices in the oil onto a conveyor from a discharge chute connected to the fishtail ramp.

Preferred features are defined in the dependent claims.

The present inventors have found that the use of the specific flume construction and corresponding process step after the lipophilic pre-conditioning step provides a uniformly high degree of slice separation into single independent slices when processing a flow of potato slices in oil for the manufacture of potato chips. The result is that the separated potato slices can be distributed on an output conveyor with at least 70%, optionally from 75 to 90%, of the slices being non-overlapping single slices. Also, the potato slices can be distributed on the output conveyor with no more than 10% of the single slices touching another single slice. Furthermore, the potato slices can be distributed on the conveyor with at least 15% coverage of the area of the conveyor by the potato slices. This allows a high production rate without causing inadvertent slice contact, overlap or clumping which could cause arcing during a subsequent microwave dehydration step, poor drying uniformity and reduced product quality. The apparatus and process of the invention are scalable, and can be employed for various mass flow rates of product therethrough.

The high degree of separation ensures that each slice sees uniform and consistent downstream processing conditions and thus receives the same product explosive dehydration and drying to achieve the final moisture content. This in turn ensures that the resultant snack food product such as a potato chip, produced by the lipophilic preconditioning and subsequent microwave explosive dehydration and drying steps discussed above, not only has low oil but also has, with a high level of product uniformity, the combination of flavour, organoleptic properties and shelf life in a non-fried potato chip which is equal or superior in consumer acceptance to conventional fried potato chips.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic perspective view of a flume in an apparatus for separating potato slices, prior to microwave cooking, according to an embodiment of the present invention;

Figure 2 is a schematic plan view of the flume of Figure 1 ; and

Figure 3 is a schematic section on line A- A in Figure 2.

An embodiment of an apparatus for separating potato slices in oil, prior to microwave cooking of the potato slices to form potato chips, according to one aspect of the present invention is illustrated in Figures 1 to 3.

Referring to the Figures, an apparatus, designated generally as 2, for separating potato slices in a supply of oil, comprises a flume 4. The potato slices typically have a thickness of 1 to 2.5 mm, more typically about 1.3 mm (51 thousandths of an inch). The oil typically comprises a vegetable oil such as sunflower oil, conventionally used for manufacturing potato chips. The oil temperature is at an elevated temperature, for example coming from a preceding lipophilic pre-conditioning step at a temperature of 90°C +/-2°C. The flume 4 comprises a gulley 6 having a flume inlet 8 at an upstream inlet end 10 and a downstream outlet end 12, and having opposed lateral walls 13, 15. The gulley 6 is rectangular, has a major length in the flow direction F and a constant width, for example 300mm. A pump 14 is connected by an outlet pipe 16 to the gulley 6 for pumping a supply of oil containing a plurality of potato slices into the gulley 6, with a horizontal inflow pipe 18 connected to the upstream inlet end 10. An inlet 20 of the pump 14 is connected by an inlet pipe 22 to a tank 24 for holding the supply of oil containing the plurality of potato slices. The tank 24 is fed from a weir 12 of an upstream apparatus, such as a lipophilic pre-conditioning unit in which the slices are submerged in heated oil for a pre-determined period.

The gulley 6 is downwardly inclined in the flow direction F at an angle to the horizontal of from 0.5 to 5 degrees, optionally 1 to 3 degrees, further optionally about 2 degrees. The inflow pipe 18 supplies a constant flow of oil containing potato slices into the gulley 6, and a corresponding constant flow of oil containing potato slices exits the gulley 6. The oil flow velocity through the flume 4 is up to 10 m/s, optionally from 0.6 to 5 m/s, typically 1.5 to 2 m/s. Such a velocity provides singulation of slices in the flume 4. The weight ratio of the potato slices to the oil in the flow through the flume 4 is from 0.5 to 3 wt%.

A fishtail ramp 24 having opposed lateral walls 26, 28 is connected at an upstream end 30 thereof to the downstream end 12 of the gulley 6. The fishtail ramp 24 progressively increases in width from the upstream end 30 to a downstream end 32 by the lateral walls 26, 28 both diverging at a constant angle relative to the flow direction along of the fishtail ramp 24. Typically, the constant angle is from 5 to 30 degrees, optionally 10 to 20 degrees, further optionally about 15 degrees. Typically, the downstream end 32 of the fishtail ramp 24 is increased in width by a factor of from 2 to 5, optionally by a factor of from 3 to 4, compared to the upstream end 30 of the fishtail ramp 24. The fishtail ramp 24 is downwardly inclined in the flow direction at an angle to the horizontal typically of from 0.5 to 5 degrees, optionally 1 to 3 degrees, further optionally about 2 degrees. A discharge chute 34, having opposed lateral walls 33, 35 is connected at an upstream end 36 thereof to the fishtail ramp 24. The discharge chute 34 has a constant width which is the same as that of the downstream end 32 of the fishtail ramp 24. The discharge chute 34 is downwardly inclined in the flow direction at an angle to the horizontal greater than the angle to the horizontal of the fishtail ramp 24, typically from 3 to 10 degrees, optionally 4 to 8 degrees, further optionally about 5 degrees. The discharge chute 34 typically has a length of from 100 to 400 mm, optionally about 200 mm.

At least one transversely extending ridge 42, 44 is mounted on an upper surface of the discharge chute 34. Alternatively, the ridges 42, 44 may be integral with the discharge chute 34. The ridges 42, 44 comprise a first ridge 42 at a junction 46 between the fishtail ramp 24 and the discharge chute 34 and a second ridge 44 at an end portion 48, in the flow direction, of the discharge chute 34. The ridges 42, 44 are typically separated by a distance of from 150 to 250 mm, optionally from 170 to 180 mm, in the flow direction. The ridges 42, 44 have a triangular cross-section, and typically a height of from 10 to 30 mm, optionally about 20 mm. The ridges 42, 44 act to slow down the flow of oil containing the potato slices as the flow exits the fishtail ramp 24.

The discharge chute 34 exits onto an output conveyor 50, typically an endless belt conveyor, which is located below the discharge chute 34 and may be oriented along or at an angle to, even perpendicular to, the flow direction. The output conveyor 50 may be horizontal or inclined at a small angle, such as up to 10 degrees, to the horizontal. The output conveyor 50 typically has a translational velocity of from 0.1 to 0.8 m/s, optionally 0.2 to 0.5 m/s.

The output conveyor 50 is mounted above an oil recovery tank 52. The output conveyor 50 is oil permeable, for example comprising an endless belt composed of metal mesh, such as stainless steel mesh. The oil can drip through the mesh into the recovery tank 52 for subsequent re-use, optionally after clean up such as water removal and/or filtering.

In the method of separating potato slices in a supply of oil, the supply of oil containing potato slices is fed into the gulley 6 from the pump 14 via the outlet pipe 16. The pump 14 is supplied from the tank 24 holding the supply of oil containing the potato slices, and fed from a weir 54.

The potato slices in the oil flow from the downstream end 12 of the gulley 6 and down the fishtail ramp 24. Since the fishtail ramp 24 progressively increases in width from the upstream end 30 to the downstream end 32, the downwardly flowing potato slices progressively and uniformly spread width wise across the width of the fishtail ramp 24. The potato slices in the oil are discharged onto the output conveyor 52 from the discharge chute 34.

The provision of a constant width for the gulley 6 along the length thereof provides a substantially uniform flow of potato slices. The distribution of potato slices within the oil is made more uniform by pumping into the gulley a high velocity supply of oil containing the potato slices. This means that the potato slices are flowed into the gulley 6 in a distribution of substantially individual single slices. Such uniform slice singulation is assisted by the shallow downward inclination of the gulley 6 at an angle to the horizontal.

The progressive symmetric increase in the width of the fishtail ramp 24, coupled with the shallow downward inclination of the gulley 6 at an angle to the horizontal, broadens the width of the output flow as compared to the input flow, and maintains uniform slice separation as the flow broadens. The downstream end 32 of the fishtail ramp 24 is increased in width by a factor of from 2 to 5, optionally by a factor of from 3 to 4, compared to the upstream end 30 of the fishtail ramp 24 correspondingly to spread the potato slices across the width of the fishtail ramp 24 as the potato slices flow down the fishtail ramp 24.

The discharge chute 34 is downwardly inclined at an angle to the horizontal greater than the angle to the horizontal of the fishtail ramp 24. The transversely extending ridges 42, 44 slow down, i.e. decelerate, the flow of oil and potato slices down the discharge chute. This combination of features provides that the potato slices are separately and independently distributed on the conveyor 50, and tend not to skid significantly when deposited onto the translating conveyor 50. This correspondingly reduces the incidence of touching potato slices on the conveyor 50. This provides that the potato slices can be distributed on the conveyor 50 with at least 70% of the slices being non-overlapping single slices, no more than 10% of the single slices touching another single slice, and at least 15% coverage of the area of the conveyor 50 by the potato slices,

The oil drips off the potato slices disposed on the conveyor 50 and passes through the oil- permeable belt into the tank 52, thereby capturing the oil for re-use.

Each slice is resident in the oil for a substantially common predetermined period, because of the substantially uniform slice flow from the gulley 6 to the conveyor 50.

The flume 6 provides that the slices have a well-defined lipophilic pre-conditioning total residence time in the oil with minimal damage to, or loss of, slices. After the lipophilic preconditioning process following deposition of the slices onto the conveyor 50, excess oil is removed in a de-oiling step, and thereafter the potato slices are subject to a pre-drying and explosive dehydration using microwave radiation, with subsequent final drying to produce the final potato chips. The oil is employed in the lipophilic preconditioning to provide the required organoleptic properties to the resultant potato chip, which has been cooked by the combination of the preliminary oil treating step and a subsequent microwave steps, and has not been fried, as for a conventional potato chip.

The various aspects of the present invention will now be described in greater detail with reference to the following non-limiting Examples.

Example 1

A flume having the structure shown in Figures 1 and 2 was provided. The flume had a gulley and a fishtail ramp each downwardly inclined in the flow direction F at an angle to the horizontal of 2 degrees. The fishtail ramp progressively increased in width from 300 mm at the upstream end to 1 m at the downstream end. The discharge chute was 1 m wide and downwardly inclined in the flow direction at an angle to the horizontal of 5 degrees. Two transversely extending ridges, a first at the junction between the fishtail ramp and the discharge chute and a second at an end portion of the discharge chute, each having a triangular cross-section and a height of 20 mm, were mounted on the discharge chute. The inflow pipe supplied a constant flow of oil containing potato slices into the gulley. The potato slices and oil were flowed down the flume and then deposited onto the output conveyor which had a belt speed of 0.2 m/s. The flow rate provided 3.6 kg/minute of potato slices.

The potato slice distribution on the conveyor had 74% single slices not overlapping other slices and 7.5 % of the single slices touching other single slices. The potato slices comprised 19% coverage of the area of the conveyor by the potato slices.

Example 2

Modification of the flume of Example 1 to omit the transversely extending ridges reduced the proportion of single slices on the conveyor to 59.6% single slices not overlapping other slices and increased to 12.1 % the proportion of single slices touching other single slices, and increased the proportion of touching chips. The ridges therefore improved the slice singulation on the conveyor.

Example 3

Modification of the flume of Example 2 to provide that the discharge chute was downwardly inclined in the flow direction at an angle to the horizontal of 19 degrees rather than 5 degrees as for Example 1 reduced the proportion of single slices on the conveyor to 57.6% single slices not overlapping other slices and increased to 15.3 % the proportion of single slices touching other single slices, and increased the proportion of touching chips. The use of a shallower angle for the discharge chute reduced slice velocity when passing onto the conveyor and consequently reduced the incidence of slices skidding into other slices, which can cause touching between slices on the conveyor. The use of a shallower angle for the discharge chute therefore improved the slice singulation on the conveyor.

Various other modifications to the illustrated embodiment will be apparent to those skilled in the art.

Claims

CLAIMS:

1. An apparatus for separating potato slices in a supply of oil, the apparatus comprising a flume comprising a gulley having a flume inlet at an upstream inlet end and a downstream outlet end, a fishtail ramp having opposed lateral walls connected at an upstream end thereof to the downstream end, the fishtail ramp progressively increasing in width from the upstream end to a downstream end, and a discharge chute connected at an upstream end thereof to the fishtail ramp, and a pump connected by an outlet pipe to the upstream inlet end of the gulley for pumping a supply of oil containing a plurality of potato slices into the gulley.

2. An apparatus according to claim 1 , wherein the gulley has a constant width along the length thereof.

3. An apparatus according to claim 1 or claim 2, wherein the gulley is downwardly inclined towards the fishtail ramp at an angle to the horizontal of from 0.5 to 5 degrees, optionally 1 to 3 degrees, further optionally about 2 degrees.

4. An apparatus according to any one of claims 1 to 3, wherein the fishtail ramp progressively increases in width from the upstream end to a downstream end by the lateral walls both diverging at a constant angle relative to the flow direction along of the fishtail ramp.

5. An apparatus according to claim 4, wherein the constant angle is from 5 to 30 degrees, optionally 10 to 20 degrees, further optionally about 15 degrees.

6. An apparatus according to any foregoing claim, wherein the downstream end of the fishtail ramp is increased in width by a factor of from 2 to 5, optionally by a factor of from 3 to 4, compared to the upstream end of the fishtail ramp.

7. An apparatus according to any foregoing claim, wherein the fishtail ramp is downwardly inclined towards the discharge chute at an angle to the horizontal of from 0.5 to 5 degrees, optionally 1 to 3 degrees, further optionally about 2 degrees.

8. An apparatus according to any foregoing claim, wherein the discharge chute is downwardly inclined at an angle to the horizontal greater than the angle to the horizontal of the fishtail ramp.

9. An apparatus according to any foregoing claim, wherein the discharge chute is downwardly inclined at an angle to the horizontal of from 3 to 10 degrees, optionally 4 to 8 degrees, further optionally about 5 degrees.

10. An apparatus according to any foregoing claim, further comprising at least one transversely extending ridge on an upper surface of the discharge chute.

1 1. An apparatus according to claim 10, wherein the at least one transversely extending ridge comprises a first transversely extending ridge at a junction between the fishtail ramp and the discharge chute and a second transversely extending ridge at an end portion of the discharge chute.

12. An apparatus according to claim 11 , wherein the first and second transversely extending ridges are separated by a distance of from 150 to 250 mm, optionally from 170 to 180 mm, in the flow direction.

13. An apparatus according to any one of claims 10 to 12, wherein the at least one transversely extending ridge has a triangular cross-section.

14. An apparatus according to any one of claims 10 to 13, wherein the at least one transversely extending ridge has a height of from 10 to 30 mm, optionally about 20 mm.

15. An apparatus according to any foregoing claim, wherein an inlet of the pump is connected by an inlet pipe to a tank for holding the supply of oil containing the plurality of potato slices.

16. A method of separating potato slices in a supply of oil, the method comprising the steps of: (a) pumping a supply of oil containing potato slices into a gulley of a flume device;

17. A method according to claim 16, wherein the gulley has a constant width along the length thereof and provides a substantially uniform flow of potato slices at the downstream end.

18. A method according to claim 16 or claim 17, wherein the gulley is downwardly inclined at an angle to the horizontal of from 0.5 to 5 degrees, optionally 1 to 3 degrees, further optionally about 2 degrees to provide a downward flow therealong.

19. A method according to any one of claims 16 to 18, wherein the fishtail ramp progressively increases in width from the upstream end to a downstream end by the lateral walls both diverging at a constant angle relative to the flow direction along of the fishtail ramp.

20. A method according to claim 19, wherein the constant angle is from 5 to 30 degrees, optionally 10 to 20 degrees, further optionally about 15 degrees.

21. A method according to any one of claims 16 to 20, wherein the downstream end of the fishtail ramp is increased in width by a factor of from 2 to 5, optionally by a factor of from 3 to 4, compared to the upstream end of the fishtail ramp correspondingly to spread the potato slices across the width of the fishtail ramp as the potato slices flow down the fishtail ramp.

22. A method according to any one of claims 16 to 21 , wherein the fishtail ramp is downwardly inclined at an angle to the horizontal of from 0.5 to 5 degrees, optionally 1 to 3 degrees, further optionally about 2 degrees to provide a downward flow therealong.

23. A method according to any one of claims 16 to 22, wherein the discharge chute is downwardly inclined at an angle to the horizontal greater than the angle to the horizontal of the fishtail ramp.

24. A method according to any one of claims 16 to 23, wherein the discharge chute is downwardly inclined at an angle to the horizontal of from 3 to 10 degrees, optionally 4 to 8 degrees, further optionally about 5 degrees to provide a downward flow therealong.

25. A method according to any one of claims 16 to 24, wherein on the discharge chute the flow is slowed by at least one transversely extending ridge on an upper surface of the discharge chute.

26. A method according to claim 25, wherein the at least one transversely extending ridge comprises a first transversely extending ridge at a junction between the fishtail ramp and the discharge chute and a second transversely extending ridge at an end portion of the discharge chute.

27. A method according to claim 26, wherein the first and second transversely extending ridges are separated by a distance of from 150 to 250 mm, optionally from 170 to 180 mm, in the flow direction.

28. A method according to any one of claims 25 to 27, wherein the at least one transversely extending ridge has a triangular cross-section.

29. A method according to any one of claims 25 to 28, wherein the at least one transversely extending ridge has a height of from 10 to 30 mm, optionally about 20 mm.

30. A method according to any one of claims 16 to 29, wherein an inlet pipe of the pump is connected to a tank for holding the supply of oil containing the potato slices.

31. A method according to any one of claims 16 to 30, wherein the conveyor comprises an oil-permeable belt located above a tank for capturing oil passing through the belt.

32. A method according to any one of claims 16 to 31 , wherein the potato slices are distributed on the conveyor with at least 70% of the slices being non-overlapping single slices.

33. A method according to any one of claims 16 to 32, wherein potato slices are distributed on the conveyor with no more than 10% of the single slices touching another single slice.

34. A method according to any one of claims 16 to 33, wherein the potato slices are distributed on the conveyor with at least 15% coverage of the area of the conveyor by the potato slices.

35. A method according to any one of claims 16 to 34, wherein the oil flow velocity through the flume device is up to 10 m/s, optionally from 0.6 to 5 m/s, typically 1.5 to 2 m/s.

36. A method according to any one of claims 16 to 35, wherein the weight of the potato slices in the flow through the flume device is from 0.5 to 3 wt% of the weight of the oil in the flow through the flume device.