GB2539539A

GB2539539A - De-oiling method in the manufacture of low oil snack food

Info

Publication number: GB2539539A
Application number: GB1606609.4A
Authority: GB
Inventors: Louise Warburg Barbara
Original assignee: Frito Lay Trading Co GmbH
Current assignee: Frito Lay Trading Co GmbH
Priority date: 2015-03-18
Filing date: 2015-03-18
Publication date: 2016-12-21
Anticipated expiration: 2035-03-18
Also published as: GB201504564D0; WO2016146814A1; GB2536626B; GB2539539B; GB2536626A

Abstract

A method of removing oil from a food slice comprises providing a belt assembly having upper and lower endless belts 16, 18, defining a product flow path 20 therebetween. Oil-coated food slices are fed along the flow path wherein the path has a height which is greater than 200% of the maximum thickness of the food slices. Water is sprayed into the oil-coated surfaces of the food slices, preferably at a mass flow rate of from 8 - 500 grams per m2 of the surface of the food slice, to form a water-and-oil-containing layer on the surface. An air jet is then applied to blow the water-and-oil-containing liquid from the surface of the slices. A plurality of air jets 38 may be applied at an air velocity of from 60 - 130 metres per second to blow away at least a proportion of the water-and-oil-containing layer. The method is of particular use in de-oiling slices of potato prior to microwave cooking to form low-oil potato crisps.

Description

DE-OILING METHOD IN TIM 'FACTURE OF LOW OIL SNACK FOOD This invention relates to a method of removing oil from are oil-coated surface of a food slice to form a snack food, This invention also relates to a method of producing a cooked snack food slice.

It has been known for to produce potato chips from slices fried ill oil, usually vegetable oil. Typical conventional potato chips have an oil content of it) 10 wt% oil, based on the total weight of the potato chip. Potato chips exhibit c organoleptic properties, incombination 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 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 tire and flavour. Even if a snack food product is produced which has high nutritional hates, 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 product's purchased.

There are An the larket so-called lawyer oil snack food products, including potato chips and other products. Some of these processes are produced by modified frying processes using it trying tern 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 5w t%, but the snack food product is not regarded by the consumer to he an acceptable alternative to a potato chip, because the product cannot exhibit the orgaiirileptic properties, in combination with the visual appearance, of a potato chip.

WO-A-2008/011489, -2009/091674 and GB-A-2481469 in the name of Frito-Lay Trading Company GmbH disclose processes for making a healthy snack food. 1n 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. lie 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 he employed, for example using microwave drying.

It is disclosed that the oil preconditioning step comprises Epop placing the slices into a warm oil flume, a batch kettle or a continti conditioning by During the kilic 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 lipophilicpreconditioning step oil removal st is etc pl yed. The of removal step is disclosed as being performed us it wet methods.

Although a wide variety of such oil removal processes is disclosed in those prior specifications, there is still a need to provide a de-oiling process which provides a lower oil content potato slice that has a consumer acceptance on parity with conventional fried potato chips. It is necessary to accurately control the de-oiling process to achieve a desired oil content after the lipophilic preconditioning step so that the resultant flavour and organoteptie properties are achieved in -the subsequent processing steps, which include microwave explosive dehydration.

Furthermore, there is still a 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 tl3vour and orgarioleptie properties, on parity with conventional fried potato chips.

There is accordingly still a need for a method for efficiently and reliably removing oil from a food slice to achieve low oil content, particularly in the manufacture of potato chips, The present invention accordingly provides a method of removing oil from an oil-coated surface of a food slice to form a snack food, the method comprising the steps of: spraying water onto the oil-coated surface of the food. slice at a water mass flow rate of from 8 -500 grains per in?. of the surface of the food slice to form a water-and-oil-containing layer on the food slice surface; and applying at least one air onto the water-and-oil-containing layer at an air velocity at the water-and-oil-containing layer of from 60 ---130 metres per second to blow at least a proportion of the water-and-oil-containing layer from the surface of the food slice, The present invention further proaric4, method of producing a cooked snack food slice, the method comprising the steps of; a, oil-blanching a food slice; b, removing oil from oil-coated surfaces of the food slice according to the method of the invention; and c. cooking the food slice to a snack od, The present invention further provides a method of removing oil from an oil-coated surface of a food slice, the method comprising the steps of; a, providing a belt assembly comprising an upper endless belt and a lower endless belt, the upper and lower endless belts defining a product. flow path therehetween; b. feeding a plurality of oil-coated food slices along the product flow path by rotation of the upper arid lower endless belts, wherein the product flow path has a height, defined between the lower and upper surfaces of the respective upper and lower endless belts, which greater than 200% of the maximum thickness of the food slices; spraying water into oil-coated surfaces of the food slices to form a water-andoil-containing layer on the food slice surfaces; and d. applying at least one air jet onto the water-and-oil-containing layer to blow at least a proportion of the water-arid-oileontaining layer from the surfaces of the food slices.

Preferred features are defined in the dependent claims.

The present inventors have found that the provision of such a sequence of specific de-oiler steps, with an initial water spray treatment at a particular mass flow rate and a subsequent atment at a particular air flow velocity can surprisingly achieve lower oil content d slice. Also, the low oil can provide a combination of flavour, orgarioleptie propel-lies and shelf life in a food slice, such as a non-fried potato chip, which is equal or superior in consumer acceptance to conventional fried potato chips. Furthermore, the surfrice water content of the potato slices is low, which avoids inadvertent arcing when the potato slices are subjected to cooking by a microwave treatment.

The present on the finding by the present ontor t wit althoughIf the surface of an oil coated food slice, such as a potato slice, air blowing alone.cannot move sufficient oil at a practical air speed, because the food slice h to remove' oil on its surface which cannot be removed solely by an air jot unless impractical, transonic air speeds (for example from Mach 0,8 to below Mach I) are employed, such as about 300 m/s. That "hard to remove" oil can be removed by first spraying the oil layer with water, and then. blowing the resultant water/oil emulsion of the tod slice surface usi ix jets are controlled not only to remove the oil, but also to provide a low free water content ira the food slices so that the food slices can be cooked. by microwave cooking without arcing. The water spray and air et treatment are carried out so as to provide, after the cooking step, an oil content on the -Iced potato slices of from 6 to 18 wt%, preferably from I i to 11 wt%, based on the total weight of the cooked potato slices, and also a total water content. of the cooked potato slices of from 5 to 8 wt%.

Embodiments of the present rove ill now he described, by way of exa apie only, with reference to the accompanying draw drawings in which: Figure 1 schematically illustrates a potato slice to he de oiledin an embodiment of the method of the present invention; Figure 2 schematically illustrates the relationship between oil film thickness and air velocity of an air jet applied to a potato slice to be de-oiled in an embodiment of the method of the present invention; U. side view of an aratus for de-oiling potato slices, prior to microwave cooking, for use in an embodiment of the method of the present invention; e 4 is a schematic plan view of a lower belt tbr use in belt assembly in an embodiment of the method. of the present invention; and e 5 is a schematic plan view of an upper belt for use in belt y in an embodiment of the method. of the present invention.

Figure 1 scherriaticall) illustrates a potato slice 2 to be de-oiled in. an embodiment the method of the present invention. The potato slice 2 is coated with oil. The oil is present in. to remove" fraction, which primarily is in an interior oil layer 4 and an "easy to remove" fraction, which primarily is in an exterior oil layer 6.

Although the present invention is described with particular reference to potat h. method of the invention may be employed. to de-oil any food slices coated with surface oil, For example, the food slices nuiy comprises slices of other vegetables, for example root vegetable such as carrot, parsnip, beetroot, sweet potato, etc or slices of dough-based ducts, which may include vegetable-and/or cereal-based dough: Figure 2 schematically illustrates the relationship between film thickness and air velocity of an air jet applied to the oil-coated potato slice 2 to be de-oiled. The "easy to remove" fraction is present at high film thickness, ol, and can be removed by air jets. At these film thicknesses, viscous forces are dominant and the oil can be removed by relatively low velocity air, optionally together with low vacuum pressure which can suck the oil droplets away from the potato slice surface. However, at smaller film thicknesses, e. closer to the surface of the potato slice, such low velocity air is in-sufficient to remove the oil, and such oil is a "hard to remove" fraction. The present inventor has found by extensive experimental research that with regard to the "hard to remove" fraction, surface tension forces are dominant and that the oil can be removed by first spraying the oil with water and then employing high velocity air jets to remove the resultant water and oil nixture from the surface of the potato slice. The high velocity air jets not only remove the "hard to remove" fraction of the oil but also remove the free water so that the resultant potato slice has controllably low surface oil content and controllably low free surface water content. The water spray and air jet treatment are-carried out so as to provide, after the cooking step, an oil content on the cooked potato slices 2 of from 6 to 18 wt°70, preferably from 11 to 13 wt%, based on total weight of the cooked potato slices 2, and also a total water content of the cooked potato slices 2 of from 5 to 8 wt%, An embodiment of an apparatus for de-ailing potato slices, prior to microwave microwave^ cooking of the potato slices to form potato chips, according to one aspect of the method of the present invention is illustrated in Figures 3 to 5.

A primary endless belt conveyor 10 in the form of a belt assembly 12 having a substantially horizontal orientation is provided, An inlet end 11 of the conveyor 10 communicates with an exit of oil flume 14 (illustrated schematically) comprising a lipophilic preconditioning unit for the potato slices 2, The conveyor 10 carries a succession of the potato slices,t conveyor 10 has a translational speed of from 0,1 to 0,5 m/secrind, typically about 0,2 &second. An outlet end 13 of the conveyor 10 communicates with an output conveyor 15 which conveys the de-oiled potato slices 2 for further processing, such as cooking by microwave radiation.

The potato slices 2 have been randomly delivered onto the conveyor 10, The potato slices 2 are delivered onto the conveyor 10 in a slice distribution so as to have at least about 50% of the. slices being single slices, i.e. not overlapping with an adjacent slice. In addition, at least 50% of the overlaps are no more than 50% of the area of each of the respective overlapping slices. Also, for each overlap no more than two slices 2 are stacked one upon the other on the conveyor 10, This substantially provides a monolayer of potato slices 2 across the length and width of the conveyor 10.

The potato slices 2 typically have a thickness of I to 2 mm, more typically about 1,3 mm (51 thousandths of an inch).

potato slices 2 have been ore-t -ed in oil in an oil-Blanching step i-h comprises lipophilically conditioning the potato slices 2 by immersion in an oil at a temperature of from 80°C to less than 100"C, preferably about 90°C, for a period of from 60 to 120 seconds, preferably about 90 seconds, After the lipophilic preconditioning process and prior to the de-oiling step the potato slices 2 have about 30 to 45 wt% surface oil, typ cally about 40 wt% surface oil based on the day weight of the final potato chip produced from the potato slice 2, In this specification the "dry weight of the final potato chip" assumes 2 water content in the total weight of the final cooked and dried potato chip, prior to final seasoning of the potato chip.

The oil typically comprises a vegetable oil such as sunflower oil, co manufacturing potato chips, Alternati the of is any other vegetable oil, optionally at least one or a mixture of at least two of ower oil, rapeseed oil and olive oil, The oil is employed in the lipophilic preconditioning to provide the required orgarnaleptic properties to the resultant potato chip, which has been cooked by the combination of the preliminary ina step and the subsequent microwave cooking step, and has not been fried, as for optional potato chip.

The belt assembly;2 comprises an upper endless belt 16 and a lower endless belt 18, which define a product flow path 20 there:between, A plurality of the oil-coated potato slices 2 are fed along the product flow path 20 by rotation of the upper and lower endless belts 16, 18. The product flow path 20 has a height, defined between the upper and lower surfaces 22, 24 of the respective alrper andlowerendless belts 16, 18, which is greater than 200% of the maximum thickness of the potato slices 2. Typically, the height of the product flow path 20 is from 220 to 300% of the maximum thickness of the potato slices The upper endless belt 16 comprises a plurality of interlinked metal links 26 having an open area of from 75 to 85% and a /ink depth of from 4 to 6 mm. Preferably, the open area is from. 80 to 85% and the link depth is about 5 ram. The plurality of intehinked metal links 26 form a rectangular grid structure in the upper endless belt 16.

The lower endless belt 18 comprises a plurality of interlinked metal links 28 having an open area of from 60 to 75% and a link depth of from 5 to 8 ram. Preferably, the open area is from 65 to 70% and the link depth is about ti mrr. The plurality of interlinked metal ks form a rectangular grid structure in. the lower endless belt 18.

As the potato slices 2 are carried on the upper surface the onveyor 10, water is sprayed from water spray nozzles 30 onto the potato slices 2 in a continuous manner at a water spray station 32 arid then air is blown downwardly onto the potato slices 2 in a continuous manner at an air-blower station 34.

At the water spray station 32 water is sprayed as a water spray 36 onto the oil-coated surface of the potato slices 2 at a water mass flow rate of from 8 -$00 grams per m2 of the surface of the potato slices 2 to form a water-and-oil-containing layer on the surface of the potato slices 2. Preferably, the ass flow rate is from 40 --80 grants per.m2 of the surface of the potato slices 2.

At the air-blower station 34, at least one air jet 38 from an xis jef noz le 40 is applied, as an air knife, onto the water-and-oll-containing laye at an:an alir' velocity at the water-and-M1-containing layer of from 60 -130 metres pet' second, The at least one air jet 38 blows at least a proportion of the water-and-oil-containing layer from the snake of the potato slices 2. Preferably, the air velocity is from 85 -130 metres per second. The at least one air jet 38 is applied at an angle of from 75 to 105 degrees to the surface of the potato slices 2, Typically, the at least one air jet 38 is applied at a s:rbstanticlly perpendicular orientation to the surface of the potato slices 2.

Each of the water spray treatment and the air jet treatment are carried out on opposite major surfaces 44, 46 of the potato slices 2, with the opposite surfaces 44, 46 being treated substantially simultaneously.

The water temperature is from 10 to 95"c, preferably m 10 to 25°C of from 70 to 90°C. The air jet temperature is from. 20 to 100°C" The temperature of the oil-coated surface prior to water impact in the water spray treatment is from 40 to 9.5°C, preferably from 50 to 80°C.

The water spray treatment and the air jet treatment are carried so as to provide, after the air atinent, a residual water content on the potato slices 2, the residual water comprising water from the water spray treatment, of from 1 to 15 wt%, preferably from 1 to 5 wt%, based on the total weight of the potato slices 2.

During the 1 ilk air flow is provided are potato slices 2 to entrain dispersed droplets of water and oil within the bulk air flow convey the droplets away from the potato slices 2. The bulk air flow is induced by suction of air away from the potato slices which is provided by at least one port (not shovsm) in at least one vacuum plenum.50 located in the vicinity of the potato slices 2. In the embodiment, plural vacuum plenums SO are provided, each opposite a respective air jet nozzle 40, The bulk air flow has an air velocity at the water-and-oil-containing layer of from 5 -90 metres per second, for example from 50 to 80 m/s, Typically the vacuum plenum.50 applies a negative pressure of from -20 to -120 mbar, for exarnple from -90 to -110 mbar. The or each port is typically located at a distance of from 3 to 25 nam, for example from 5 to 15 mm, from the surfaces of the potato slices 2, During the water spray and. air jet treatment, the potato slices 2 are supported reained within the specifically configured. belt assembly 12 which not only holds the potato ices 2 against being blown of by the water spray 36 or air jet 38 but also permits water and air transmission therethrough to ensure effective oil removal.

As described above, water is sprayed onto the oi. d surfaces of the potato slices 2 to form a water-and-oil-containing layer on the surfaces of the potato slices 2 and then at least one air jet 38 from an air knife is applied onto the water-and-oil-containing layer to Now at least a proportion of the water-and-oil-containing, layer from the surfaces of the potato slices 2. The plurality of air jets 38 are applied at a downstream location, with respect to the flow of the potato slices 2 along the product flow path, e to the water spray 36.

The water is sprayed both downwardly and upwardly against the upper and lower surfaces 44. 46, respectively, of the potato slices 2, 'The water is sprayed downwardly against the upper surface 44 of the potato slices 2 at least partly when the potato slices 2 are supported on the lower endless belt 18 upstrearri of the product flow path and prior to engagement of the potato slices 2 by the upper endless belt 16. The water is sprayed upwardly against the lower surface 46 of the potato slices 2 at least partly *hen. the potato slices 2 are supported on the lower endless belt 18 upstream of the product flow path and prior to engagement of the potato slices 2 by the upper endless belt 16. The water is also sprayed upwardly against the lower surface of the potato slices 2 at least partly when the potato slices 2 are in the product flow path between the upper and lower endless belts 16, 18. The water is sprayed both downwardly and upwardly, at. least partially simultaneously and at least partially sor.hentially, against the upper and lower surfaces 44, 46, respectively, of the potato slices The at least one et 38 is applied tc the potato slices 2 potato slices 2 are in the product flow path and between the upper and lower endless belts 16, 18. The plurality ets 38 are applied. both downwardly and upwardly against the upper and lower surfaces 44, 46, respectively, of the potato slices 2, At least one of the plurality of air 38 is applied upwardly against the lower surface 46 of the potato slices 2 at an upstream location, with respect to the flow of the potato slices 2 along product flow path, relative to at least one the plurality of air jets 38 which is applied downwardly against the upper surface 44 of the potato slices 2.

By providing that the product flow path 20 has a height; defined between the upper and lower surfaces 22, 24 of the respective upper and lower endless belts 16, 18, which is greater than 200% of the maximum thickness of the potato slices 2, in the absence of any net upward force on the potato slice 2 from a water spray or an air jet causing, the potato slice to be at least partially lifted off the lower endless belt 18; an upper surface of the potato slice is substantially free from contact with the upper endless belt 16. By providing essentially no or minimal contact between the upper surface of the potato slice 2 and the upper endless belt 16, this has been found to achieve an additional 2.5 wt% reduction in the water content of the potato slice 2, by removal of surface water using the air jets, as compared to constant contact of the upper surface of the potato slice 2 and the upper endless belt 16. Correspondingly, one or more lower air jets causes the potato slice to be at least partially lifted off the lower endless belt 18 at least once, and this has been found to achieve an additional reduction in the water content of the potato slice 2, by removal of surface water uaing the air jets, as compared to constant contact of the lower surface of the potato slice 2 and the lower endless belt 18.

After the removal of the oiltoil-coated surfaces of the potato slices 2, the potato slices 2 are cooked, ler example by microwave cooking, to form a snack food, in this embodiment potato chips. hi the microwave cooking step, the balk moisture content of the slices 2 is reduced from an average value of at least 7S yt%, wt%, based on the total weight of the potato slices 2 to an average bul of f/0111 5 to 8 wt% based on the total weight of the potato slices 2. The microwave cooking step is carried out for a period of from 60 to 360 seconds, preferably from 120 to 300 seconds. The microwave energy has a frequency of from 875 to 925 MHz, optionally about 900 Mhz.

The water spray and air jet treatment are carried so as to pro Ise cooking, an oil content on the cooked potato slices 2 of from 6 to 18 n preferably from 11 to 13 wt%, based on the total weight of the cooked potato slices 2, and also a total water content of the cooked potato slices 2 of flout S to 8 wl The moisture content is then reduced further by finish drying, a final moisture content for the potato slices of 2 +/- wt% based on the dry weight of the potato chip.

The fir tent amount in the potato slices 2 1s achieved by balancing the amount of water and the amount of air supplied. It sible use more air and less water* and vice versa to fine tune the de-oiling operation and the final oil content. The target final oil content for the potato slices using the de-oiler is i2.5 wt% oil +I-2 wt% based on the dry weight, having 2 4-/-0,5 wt% water content, of the final cooked and dried potato chip after microwave explosive dehydration arid final drying, in modifications to the illustrated embodiment, the he nu, of air knives and/or water spray stations may be varied.

Claims

I. A method of removing oil from an at tb0C1;11.1u:ndless comprising the steps of; a. providing a belt assembly comprising an upper endless belt belt, the upper and lower endless belts defining a product flow path therebetween; b. feeding a plurality o oil-coated food slices along tb.e product flow path by rotation of the upper and lower endless belts, wherein the product flow path has a height, defined between the lower and upper surfaces of the respective upper and lower endless belts, which is greater than 200% of the maximum thickness of rhe food slices; c. spraying water onto oil-coated surfaces of the food slices to form a water-andoil-containing layer on the food slice surfaces; and ci. applying at least one air jet onto the Water-and oil-contrilning layer to blow at least a proportion of the water-and-oil-containing layer from the surfaces of the food slices.

A method according ac sors ing to claim I wherein tae height of the product low path is from 220 to 300% of the maximum thickness of the food slices.

A method according to claim I or claim 2 wherein absence of an upward force on the food slice from a water spray or an air jet causing th slice to he at least partially lifted off the lower endless belt, an upper surface of the Mod slice is substantially free from. contact with the. upper endless belt.

4"0i. method according to any one of claims I to 3 wherein one Of more air jets causes the lbod slice to be at least partially lifted off the lower endless belt at least mace during step d.

5. A method according to any one of claims l to 4 wh re n the water is sprayed both downwardly and upwardly against the upper and lower su faces, respectively, of the food slices.

6. A method according to cl rater is sprayed both. dove:a arch), and upwardly, at least partially simultaneously, against the upper and lower surfaces, respectively, of the food slices.

7, A method accord( 6 whereinis sprayed both r.upwardly, at least partially sequentially, against the upper and lower surfaces" respectively, of the food slices, 8. A method according to any one of claims 1 to i wwherein the water is sprayed. downwardly against the upper surface of the food slices at least partly when the food slices are supported on the lower endless belt upstream of the product flow path and prior to engagement of the food slices by the upper endless halt.9. A method according to any one of claims I to 8 wherein the water is sprayed upwardly against the lower StillaCe of the food slices at least partly when the food slices are supported on the lower endless belt upstream of the product flow path and prior to engagement of the food slices by the upper endless belt 10. A method according to any one of claims I to 9 wherein the watersprayed upwardly against the lower surface of the food slices at least partly when the food slices are in the product flow path between the upper and lower endless belts, 11, A method according to any one of claims 1 to 10 wherein the at least one air let. is applied to the food slices when the food slices are in the product flow path and between the upper and lower endless belts.12. A method according to any one of claims 1 to 11 wherein plurality of the air jets are applied both downwardly and upwardly against the upper and lower surfaces, respectively, of the food slices, 13, A method according to claim 12 wherein the plurality of air applied zit downstream location, with respect to the flow of the food slices along the product now path, relative to the water spray.14"as method according to claim 12 or claim 1. wwhe.rein at least one of the plurality of air jets is applied upwardly against the lower surface of the food slices at an upstream location, with respect to the flow of the food slices along product flow path, relative to at least one the plurality of air jets which is applied downwardly against the upper surface of the food slices.15. A method according to any one of claims I to 14 wherein the water ate of water sprayed in step c is f our 8 -500 grams per m2 of the surface of the feed slice, optionally from 40 - arrif, per in' of the s;cod slice.according;, to any one the air least one air jet is from 60 -130 er second, optionally from frrnr 8.5 -13 metres per second.17, A method. according to any one of claims I to 16 whetein the at least one air jet is applied at an angle of from 75 to 105 degrees to the surffice of the food slice.18. A method according to claim 17 wherein the at least one air jet is applied at a substantially perpendicular orientaiion to the surface of the food slice.19, A method according to any one of claims 1 to 18 wherein the lower endless belt comprises a plurality of interlinked metal links having an open area of from 60 to 75% and a link depth. of from 5 to 8 mm, optionally an open area of from 65 to 70% and a link depth of about 6 nun.20. A method according to claim 19 wherein the plurality of in form a rectangular grid stricture in the lower endless belt.21. A method according to any one of claims 1 to 20 wherein the upper ndless belt comprises a plurality of interlinked metal links having an open area of from 75 to 85% and a. link depth of from 4 to 6 mm, optionally an open area of from 80 to 85% and a link depth of about 5 mm, oil according to claim 21 wherein the plurality of interlinke metal links form a rectangular arid structure in the upper endless belt.23. A method according to any one of claims 1 to 22 wherein the fipod slice is potato 24. A method according to clai wherein the potato si has a thickness of from 1 to 2 nun.