GB2324952A

GB2324952A - Low fat potato crisps

Info

Publication number: GB2324952A
Application number: GB9708932A
Authority: GB
Inventors: Robert Mitchell Rolston; Garfield George Evans; Debra Rycraft
Original assignee: United Biscuits Ltd
Current assignee: United Biscuits Ltd
Priority date: 1997-04-30
Filing date: 1997-04-30
Publication date: 1998-11-11
Also published as: GB9708932D0

Abstract

A process for the manufacture of a vegetable snack product comprises cutting a vegetable to obtain vegetable slices; applying to the vegetable slices an edible oil, to obtain oiled slices; and baking the oiled slices to obtain baked slices having a moisture content of not more than 3% by weight based on the total weight of the baked slices; said baking comprising a step in which the oiled slices are exposed to radiation of near-IR wavelength. The vegetable snack product so obtained has a relatively low fat content, whilst having good textural properties.

Description

Improvements in and relating to the manufacture of snack products The present invention relates to methods of manufacturing snack products and to snack products. The invention is especially concerned with methods for the manufacture of lower-fat snack products and with the lower-fat snack products so obtained.

The term "lower-fat" as used herein in relation to products is to be understood as meaning that the products are of reduced fat content as compared with comparable products made by a process including a deep-frying step.

In general, products referred to herein as "lower-fat" products have a fat content that is lower than that of a comparable deep-fried product by an amount of at least 5% by weight, based on the total weight of the deep-fried product. The term "fat" as used herein includes, and generally refers to, oil.

In the past, many snack products have been made by processes including a deep-frying step in which the products are immersed in oil. During such a frying step a significant amount of oil is absorbed by the product as it fries, and the resultant product has a relatively high fat content. For example, where potato crisps are manufactured by frying potato slices until their moisture content has been reduced to not more than 2 by weight, the fat content of the finished crisps may be in the range of from 30 to 40% by weight, based on the total weight of the crisps.

In recent years, there has been an increasing demand for snack products which have a lower fat content than snack products which have been cooked by frying.

In one previously known method of manufacturing lower-fat potato crisps, slices of potato have been fried until their water content is of the order of 10% by weight, and then dried until their water content is not more than 2t by weight. The fat content may then be, for example. 25% bv weight. based on the total weiaht of the crisps. That method, however, can produce only a limited reduction in the fat content; if the pieces are removed from the fryer earlier so that there is less fat absorption, and a higher proportion of the water is removed in the dryer, the quality of the resulting product is unsatisfactory.

In the case of lower-fat products that have a relatively high moisture content, the effects of fat may be simulated by other ingredients, for example gums, which may be included instead of fat. Whilst such gums could be incorporated as an ingredient in a mixture of ingredients, for example a dough, from which a snack is obtained, that possibility is not available in the case of snack products made from slices of vegetable. There is a tendency for lower-fat snack products made from slices of vegetable to have a hard and dry texture, which is perceived by consumers to be undesirable.

Accordingly there is a need for a process for the manufacture of snack products of reduced fat content, but which nonetheless have a product quality, for example, flavour and texture, which will be attractive to consumers.

The present invention provides a process for the manufacture of a vegetable snack product comprising: cutting a vegetable to obtain vegetable slices; applying to the vegetable slices an edible oil to obtain oiled slices; and baking the oiled slices to obtain baked slices having a moisture content of not more than 3% by weight based on the total weight of the baked slices; wherein said baking comprises a step in which the oiled slices are exposed to radiation of near-infrared (near-IR) wavelength.

The term "near-IR" is used rein in relation to wavelength to mean a wavelength from 0.75 to 2.5cm.

The process of the invention allows the manufacture of lower-fat products which, notwithstanding their relatively low fat content as compared with comparable products made by a process in which the cooking step is a deep-frying step, have good texture characteristics, flavour and appearance, and are thus of a quality acceptable to consumers.

It has been found, in accordance with the invention, that infrared (IR) radiation of near-IR wavelength (that is, in the range of 0.75 to 2.SAm) can give relatively even heating of vegetable slices, as compared with IR radiation of wavelengths greater than 2.5cm. Radiation of near-IR wavelength is able to penetrate relatively deeply into the slices, and in the case of slices of the thicknesses typically used in accordance with the invention, a proportion of the near-IR radiation is found to be transmitted through the whole thickness of the slice. In contrast, IR radiation of wavelengths greater than 2.5m tends to be absorbed in the vicinity of the surface of the slice on which the radiation is incident, and can lead to rapid dehydration of that surface. As a result, where slices are exposed only or substantially only to radiation of wavelengths greater than 2.5cm, the surface of the slice may become overcooked or unacceptably dry before the interior of the slice has been cooked to the desired extent. Advantageously, the near-IR radiation is of wavelengths from 0.9 to 1.6cm, and especially 1.0 to 1.5cm.

In practice the near-IR-irradiation will typically be carried out in an IR oven, usually a tunnel oven, having as the source of the radiation at least one, and usually a series of, radiant heating elements. The proportion of the radiation emitted by radiant heating elements in the near-IR band of wavelengths depends on the operational temperature of the elements. It will be appreciated that there should therefore be selected one or more radiant heating elements having an operational temperature which is such that the emitted radiation includes a suitable proportion in the near-IR band of wavelengths. Commercially-available electrically energisable radiant heating elements that, at their normal operating temperatures, emit radiation including a suitable proportion of radiation in the near-IR band of wavelengths include halogen-filled or evacuated quartz tubes with tungsten filaments.

In practice, it has been found that, when such sources have operational temperatures of not less than 16000C, radiation of which a suitable proportion is in the near-IR band of wavelengths is obtained.

Advantageously, the operational temperature of the or each source exceeds 20000C, and is preferably in the range of from 2100 to 23000C.

The use of infrared radiation in the cooking of snack products has been proposed previously (see International Patent Specification 96/39867 and US Patent Specification 4,800,900), but those earlier specifications teach that the use of oil is to be avoided completely. The products obtained in accordance with the present invention have improved texture and flavour as compared with the products obtainable in accordance with those previously proposed methods. US Patent Specification 4,749,579 proposes the use in crisp manufacture of drying and pre-heating steps in which, after washing in an aqueous solution, the potato slices are dried and pre-heated using IR radiation before being fried. As a result of the removal of moisture before frying, the frying time is shorter and the fat uptake is lower, with the fried crisps in consequence having a fat content of from 26 to 32% by weight. The removal of more moisture from the slices in the drying and pre-heating steps is possible, but the products so obtained are inferior in texture. It is believed that that is in part because the lower water content means that less steam is generated during frying and as a result insufficient expansion of the slices occurs during frying. Also, if the drying and/or pre-heating step is so extended that a greater amount of water is removed, the outer surfaces of the slices may become dry and increase in rigidity, and that may similarly reduce the amount of expansion that can occur and thus affect detrimentally the texture of the product. In the process of the present invention it is believed that the presence of the oil during the near-IR irradiation contributes to reduction or elimination of the occurrence of such hardening of the outer surfaces, enabling an improved product to be obtained.

Preferably, the vegetable is potato, the cooked slices obtained in accordance with the process being potato crisps. As already mentioned, it is typical for the fat content of potato crisps to be in the range of from 30 to 40% by weight, based on the total weight of the crisps. In accordance with the present process, it is possible to obtain potato crisps with a fat content of not more than 25%, and preferably not more than 19%, by weight, based on the total weight of the crisps, but which are of good texture, flavour and eating quality.

Preferably, the oil is applied to the slices in such an amount that immediately before the near-IR irradiation the oil content of the slices is at least 2% by weight, based on the total weight of the slices. Preferably, the oil is applied to the slices in such an amount that immediately before the near-IR irradiation the oil content of the slices is not more than 8W by weight based on the total weight of the slices.

The oil may be applied to the slices by spraying.

It will generally be desirable to use an oil application method, for example a spraying method, which results in oil being applied to both sides of the slices. It has been found that, even where the slice is irradiated from one side only, the quality of the product obtained is better where oil is applied to both sides of the slices before the near-IR treatment.

Where the term "oil" is used herein in relation to a substance, that is not to be taken as implying that the substance in question is liquid at room temperature.

Advantageously, on exposure of the slices to the near-IR radiation the mean heat flux incident on at least one slice surface is in the range of from 15kW/m2 to 80kW/m2 for a period of from 15 to 180 seconds.

References herein to heat flux incident on a slice surface are to the total radiant heat flux incident on the slice surface, including radiation that is of wavelengths outside the range of from 0.75 to 2.5m and thus does not constitute near-IR radiation as defined herein. The heat flux incident on the slice surface may be determined by placing a suitable sensor surface at the position in the oven that, when carrying out the process, would be occupied by the slice surface. Suitable heat flux sensors and heat flux measurement using those sensors are described in UK Patent Specification No.

2 183 346A and in our earlier UK Patent Application No.

9617912.2. Heat flux values in that range are preferred as they have been found to produce adequate heating throughout the slices. At higher heat flux values, in contrast, preferential cooking of the proximal surface is obtained and, especially where irradiation is from one side of the slice, there may be unacceptable variations in the degree to which the slice has been cooked from one side to the other. Preferably, the heat flux incident on at least one slice surface is in the range of from 15kW/m2 to 45kW/m2. Preferably, the duration of the exposure of the slices to the near-IR radiation is in the range of from 90 to 140 seconds.

In the process of the invention a substantial proportion of the water contained in the slices (in general, more than one half) may be removed by said near IR treatment, with the moisture content being further reduced in a subsequent step which may be, or may include, any suitable baking method. In the context of this specification, the term "baking" is to be understood as including any process in which the water content of slices is reduced in a gaseous medium, especially in air, preferably at atmospheric pressure. It will be appreciated that the subsequent step is not to include a deep-frying step. Advantageously, the baking further comprises a drying step subsequent to the exposure to near-IR radiation, the drying step comprising heating the slices in hot air. Advantageously, the temperature of the hot air and the time during which the slices reside therein are so selected that the moisture content of the slices is reduced by said drying step to the said value of not more than 3% by weight, based on the total weight of the baked slices. The temperature of the hot air may be, for example, 80 to 2000C, more preferably 120 to 1800C. Advantageously, the moisture content of the slices is reduced by the near-IR treatment to not more than 40t by weight, based on the total weight of the slices immediately after said near-IR treatment, the moisture content being further reduced in said drying step. The moisture content of the slices is preferably reduced by said near-IR treatment to not more than 25% by weight, based on the total weight of the slices immediately after said near-IR treatment.

Where the baking method used for the further reduction of the moisture content is or includes drying the slices in hot air, it is advantageous for the slices to be heated in air at a temperature of not less than 1200C, as the surfaces of the slices may then become browned, enhancing the appearance of the snack products.

The duration of the time during which the slices are exposed to air at such temperatures must, however, be so controlled that the amount of browning does not exceed a level which is regarded as acceptable. It has been found especially advantageous for the slices, after said exposure to near-IR radiation, to be heated in hot air at a temperature of not less than 1200C, and preferably at about 1600C, for a period of up to five minutes, and further heating the slices in hot air at a temperature of from 800 to 1300C, and preferably at about 1200C, for a period of up to fifteen minutes. In such a two-part drying step, a desirable amount of browning of the slices is achieved at the higher temperature with further drying to the final desired moisture content being carried out at a lower temperature at which little or no browning occurs.

Advantageously, the fat content of the slices immediately before the drying step is from 1.75 to 20W by weight based on the total weight of the slices.

The fat content of the vegetable snack product may be not more than 25%, advantageously from 3 to 25%, and preferably from 8 to 19%, by weight, based on the total weight of the product. Whilst it is preferred for the fat content of the snack product to be from 8 to 19% by weight, it is nevertheless possible to manufacture products, including potato crisps, with lower fat contents, for example about 5% by weight, those products having acceptable texture and flavour notwithstanding their low fat contents.

Advantageously, the moisture content of the vegetable snack product is not more than 2% by weight, based on the total weight of the product.

Fat contents referred to herein may be determined by any suitable method. For example, they may be measured by the "Soxtec method?? in accordance with which the product is crushed, a 2g portion of the crushed product is mixed with acid-washed sand and finely ground using a glass rod, and then extracted for 15 minutes using 30ml boiling di-ethyl ether, the ether is placed in a preweighed dry aluminium Soxtec cup, the Soxtec cup is dried between 1000C and 1050 to constant weight, and the fat content is calculated from the increase in the weight of the Soxtec cup. The moisture contents of the cooked product referred to herein as being by weight, based on the total weight of the products, may be determined, for example, by drying the previously weighed products in a fan oven at 1030C for four hours and then re-weighing.

One form of process according to the invention for producing a snack product from potatoes will now be described, by way of illustration, with reference to the accompanying drawings, in which: Fig. 1 is a flow diagram indicating the main steps in the process; Fig. 2 is a vertical section through a sprayer, shown diagrammatically, for use in the process; Fig. 3 shows diagrammatically a portion of the sprayer of Fig. 2, on a larger scale; and Fig. 4 is a vertical section through an infrared oven, shown diagrammatically, for use in the process.

With reference to the drawings, in Fig. 1 reference numeral 1 indicates a peeler, for example, a steam peeler or an abrasion peeler, for peeling washed raw potatoes.

Downstream of the peeler 1 is a slicer 2, for example, an Urschel slicer, to which the peeled potatoes are conveyed. The potatoes are sliced by the slicer 2, and the slices so obtained, which are preferably about 1.4mm thick, are delivered onto a conveyor belt.

The slices are conveyed through a washer 3, which contains a reservoir of water at a temperature of from 12 to 600C, generally at 150C, in which the slices are immersed to remove free starch adhering to their surfaces. Reference numeral 4 represents a further washer, which is arranged to immerse the slices in water at a temperature of 60 to 990C, and generally 75 to 850C.

Inclusion of such a further wash, at relatively high temperature, is optional, but is preferred where the sugar content of the raw potatoes exceeds 0.25% by weight. In each case, the slices may be washed by spraying instead of by immersion. Downstream of the washer 3 and, if present, the further washer 4 is surface-moisture removal means 5, for example, of a type manufactured by Heat and Control, Inc. and known as an Air Knife (trade mark) in which a stream of air, which may, for example, be at a temperature of from ambient to 1200C is directed at the surfaces of the slices to remove surface moisture.

From the surface-moisture removal means 5, the slices are conveyed to an oil applicator 6, which is shown diagrammatically in Figs. 2 and 3. The oil applicator 6 comprises a housing 61 through which passes the upper run of a conveyor belt 62 made of mesh or parallel strands of wire on which slices are carried in a monolayer. Two upper sets 63a, 63b and two lower sets 64a, 64b of rotary sprayer discs are mounted above and below, respectively, the upper run of the belt 62 for spraying oil onto both surfaces of slices lying on the belt. Each set of sprayer discs 63a, 63b, 64a and 64b, respectively, comprises a pair of dish-shaped discs which are mounted to rotate about central axes. Fig. 3 shows schematically the spray pattern of oil 0 onto the belt 62 from the set of discs 63a. Although, as already mentioned, each set of sprayer discs 63a, 63b, 64a and 64b may comprise a pair of discs, it may comprise only one, or three or more such sprayer discs. In addition, instead of two sets, there may be only one set, or three or more sets, of upper and lower sprayer discs arranged along the path of the belt 62 through the housing 61.

The discs 63a, 63b, 64a and 64b are driven by an electric motor (not shown). Where each set comprises two or more discs, the direction of rotation of each disc may be selected to be the same as, or opposite to, that of the or each adjacent disc in the same set, with the object of obtaining an even delivery of oil across the width of the belt.

Pipework 65 is arranged to deliver preheated oil to the centre of each of the rotary sprayer discs 63a, 63b, 64a and 64b so that, in use, oil is sprayed by the discs onto upper and lower surfaces of the slices on the belt 62 in the directions indicated by arrows 0. The oil is supplied to the pipework 65 by a pump 66 from a sump 67 located at the base of the housing 61 on a support 68.

The sump 67 also serves to collect excess oil E sprayed by the discs 63 and 64 and deposited on the walls of the housing 61 and other parts of the apparatus. The sump 67 is replenished with oil from a reservoir (not shown), the level of oil in the sump being maintained between upper and lower levels, for example, by means of probes (not shown) extending into the sump at those levels and arranged to cause oil to be delivered from the reservoir when it falls to the lower level in the sump and to stop delivery when it reaches the upper level. Alternatively, oil may be supplied to the sump 67 from the reservoir at a constant rate sufficient to replenish continuously the oil delivered by the sprayer and not recovered in the sump, that rate being readily determined in practice.

The oil pipework 65 may be surrounded by a water jacket (not shown) to maintain the oil within the pipework at the desired application temperature during operation and, further, to melt solidified oil, if required, when operation of the oil applicator 6 is initiated. Control means (not shown) for adjusting the speed of rotation of the discs and the temperature of the oil is also provided. An air outlet 69 fitted with a filter 69a to prevent the escape of oil droplets entrained in the air may be provided in the uppermost part of the housing 61.

The oil applicator 6 for spraying slices on a production scale may be, for example, an Arcall rotary disc sprayer having a conveyor belt of a width of 0.813m arranged to travel at, for example, a speed of from 30m/min to 45m/min.. The total length of the run of the conveyor belt through the housing of the sprayer may be 3m. The discs may be arranged to rotate at 2000rpm and the oil may be at a temperature of 500C.

Downstream of the oil applicator 6 is an infra red oven indicated generally by the reference numeral 7 and shown diagrammatically in Fig. 4. A monolayer of slices having been sprayed with oil in the oil applicator 6 is arranged to travel through the oven 7 on the upper run of a conveyor 71 having a belt of mesh or parallel wire strands. The oven has a housing 72 comprising an upper section arranged above the conveyor 71 and designed to hold, for example, three infra red heating cassettes 73.

Each cassette 73 comprises, for example, six infra red heating elements 74 arranged parallel to each other and extending transversely across the conveyor. The vertical separation of the heating elements 74 from the conveyor 71 (measured from the lowermost part of the surface of each element to the uppermost surface of the upper run of the conveyor) is, for example, 0.08m, but means (not shown) is provided for each of the cassettes 73 to enable adjustment of the vertical separation of that cassette from the conveyor, and consequently of all the heating elements of that cassette, to a distance within the range of, for example, 0.05 to 0.14m. The heating elements 74 of each cassette can also be switched on or off independently of each other so that the total heat flux emitted by each cassette can be adjusted. Each cassette 73 also comprises a cooling fan 75 (shown schematically), and has an inner reflective surface 73a arranged to reflect radiation emitted by the elements downwardly onto the conveyor 71. The housing 72 has a lower section arranged beneath the return run of the conveyor 71 which comprises a reflector plate 76 arranged to reflect radiation reaching it back onto the lower surfaces of slices on the conveyor.

Each of the infra red heating elements 74, which may be, for example, commercially-available halogenfilled or evacuated quartz tubes with tungsten filaments, has an operational temperature within the range of from 2000 to 23000C and a peak emission wavelength (that is to say, the wavelength of the radiation of the element at which the emitted heat flux is calculated as greatest) within the range of from l.0m to 1.3cm. By adjusting the vertical separation of each cassette 73 of heating elements 74 from the conveyor 71 and adjusting the number of heating elements operating in each cassette by switching each element on or off individually, the heat flux received by the slices as they travel through the oven 7 can be adjusted. In use, the mean heat flux received by the uppermost surfaces of the slices may be adjusted to be, for example, within the range of from 15 to 45kW/m2 as they pass through the oven 7.

The length of the oven in the direction of travel of the conveyor may be, for example, 1.3m and the residence time of the slices in the oven within the range of from 15 to 180 seconds.

Downstream of the oven 7 is a packed bed dryer 8, in which the slices are conveyed through a stream of air at a temperature of 100 to 2000C, for example, from 120 to 1800C. After treatment in the bed dryer, the slices may be transferred to a packaging apparatus 9 for packaging.

In use, washed raw potatoes with a specific gravity of 1.07 to 1.20, typically from 1.09 to 1.105, and with a moisture content of from 74 to 81% by weight are introduced into the peeler 1. Peeled potatoes are then fed to the slicer 2, where they are sliced to give slices of thickness 0.045 to 0.065 inches (1.1 to 1.7mm). The slices are conveyed through washer 3, in which the slices are washed with water at a temperature of from 12 to 600C for a period of from 10 seconds to 3 minutes, for example, for 2 minutes, to remove free starch adhering to the slice surfaces. Thereafter, if the potatoes have a sugar content of 0.25 or more, the slices are subjected to a hot-washing step in washer 4, in which they are washed in water of temperature 60 to 99"C for from 20 seconds to 6 minutes, for example, for 2 minutes. It will be appreciated that the temperature and duration will need to be selected according to the sugar content of the potatoes and, in particular, having regard to the need to induce sugar leaching of a level sufficient to reduce the sugar content of the slices to less than 0.25% by weight. The slices from the washer 3 or, where used, the washer 4 typically have a surface moisture content of 12 to 13W by weight, based on the total slice weight.

The surface moisture content is to be understood as referring to moisture that may be removed by an absorbent towel contacting the slice and may conveniently be measured by placing the previously weighed slices on absorbent paper towelling, for example, Kimberley-Clark Kim-Whites (trade mark) - 71SG, for 30 seconds, turning the slices over onto fresh absorbent paper towelling for a further period of 30 seconds, re-weighing the slices and calculating the weight loss. The weight loss, expressed in per cent based on the weight of the slices before removal of the surface moisture, represents the surface moisture content of the slices.

The slices are conveyed through the Air Knife (surface-moisture removal means 5), which removes surface moisture. The temperature and air velocity of the Air Knife are so selected that the slices start to become elevated by the air current. On exit from the Air Knife, the moisture content of the slices is typically 74 to 81% by weight, based on the total weight of the slices.

The slices, arranged in a monolayer, are then conveyed through oil applicator 6, in which oil, for example, palm olein at 500C is sprayed onto the slices by the sprayer discs 63a, 63b, 64a and 64b rotating at 2000rpm. The throughput of the oil applicator 6 may be approximately 1150kg of slices per hour. On exit from the applicator 6, the slices are oiled on both sides.

Immediately after application of the oil, the slices may have an oil content of 2 to 8% by weight, and a moisture content of 68 to 80W by weight, in each case based on the total weight of the slices. The oiled slices are conveyed in a monolayer through the IR oven 7, the residence time in the oven being from 15 to 180 seconds, and preferably from 90 to 140 seconds. On exit from oven 7, the slices may have a moisture content of from 10 to 40% by weight, and an oil content of from 1.75 to 20% by weight, in each case based on the total weight of the slices. The slices are then formed into a layer from 1 to 15cm deep, for example, from 2 to 10cm deep, and are then conveyed through the packed bed dryer 8. The residence time of the slices in the dryer may be from 3 to 15 minutes, for example, from 4 to 7 minutes.

On exit from the dryer 8, the slices are packaged in packaging apparatus 9. The moisture content of the final product is preferably in the range of from 0.4 to 2% by weight, based on the total weight of the product.

The fat content may be from 3 to 25% by weight, for example, from 8 to 19% by weight, based on the total product weight.

The following Example illustrates the invention.

Example 3Kg of potatoes (Saturna) were washed and peeled to provide raw potatoes with a moisture content of 81% by weight, based on the total weight of the raw potatoes.

The peeled potatoes were then sliced to a thickness of 56 thousandths of an inch (1.4mm).

The slices were then submerged in water at 300C for 2 minutes, the water being agitated to enhance the washing off of free starch at the slice surfaces. The surface moisture was removed from the washed slices using an Air Knife operating at 900C, the moisture content thereafter being 76 by weight, based on the total weight of the slices.

Oil which had been heated to 500C was then sprayed on both sides of the slices to give slices having an oil content of 5.7 and a moisture content of 71.7%, in each case by weight, based on the total weight of the slices after spraying. The slices were then arranged in a temperature of the heating elements was in the range of from 2200 to 23000C, with all of the elements being switched on. The vertical separation of the heating elements from the upper run of the conveyor was selected to be 0.08m. The mean heat flux received by the uppermost surfaces of the slices was found to be of the order of 23kW/m2 under those conditions. The peak emission wavelength was about l.lym. The residence time was 2 minutes. On exit from the oven the oil content of the slices was 12.1t, and the moisture content was 18%, in each case by weight, based on the total weight of the slices on exit from the oven. Thus, approximately 90% of the water present in the slices on entry to the oven had been removed in the IR irradiation step.

The slices were then finished in a packed bed conveyor dryer. A packed bed of slices of 5cm in depth was attained by running the packed bed conveyor at a slower speed than the conveyor in the IR oven, from which the slices were fed onto the packed bed conveyor. The air entered the bed through a perforated plate under the conveyor at a temperature of 1600C and a velocity of approximately 2m/s. The residence time in the dryer was approximately 7 minutes. On exit from the dryer, the oil content was 13% and the moisture content was 1.4%, in each case by weight, based on the total weight of the product. The slices exited from the IR oven at a rate of 2.3Kg/hour and from the dryer at a rate of 1.8Kg/hour. The products were judged to have satisfactory texture and flavour, notwithstanding their relatively low fat content.

It will be appreciated that the method described in the Example does not give product on a scale suitable for commercial production. The scaling up of the method is, however, a straightforward matter, suitable apparatus for use on production scale being described above.

Claims

1. A process for the manufacture of a vegetable snack product: comprising cutting a vegetable to obtain vegetable slices; applying to the vegetable slices an edible oil to obtain oiled slices; and baking the oiled slices to obtain baked slices having a moisture content of not more than 3% by weight based on the total weight of the baked slices; wherein said baking comprises a step in which the oiled slices are exposed to radiation of near-IR wavelength.

2. A process as claimed in claim 1, in which the vegetable is potato, the baked slices obtained in accordance with the process being potato crisps.

3. A process as claimed in claim 1 or claim 2, in which the oil is applied to the slices in such an amount that immediately before the near-IR irradiation the oil content of the slices is at least 0.75% by weight, based on the weight of the slices.

4. A process as claimed in any one of claims 1 to 3, in which the oil is applied to the slices in such an amount that immediately before the near-IR irradiation the oil content of the slices is not more than 8% by weight based on the weight of the slices.

5. A process as claimed in any one of claims 1 to 4, in which the oil is applied to the slices by spraying.

6. A process as claimed in any one of claims 1 to 5, in which on exposure of the slices to the near-IR radiation the mean heat flux incident on at least one slice surface is in the range of from 15kW/m2 to 80kW/m2 for a period of from 15 to 180 seconds.

7. A process as claimed in claim 6, in which on exposure of the slices to the near-IR radiation the mean heat flux incident on at least one slice surface is in the range of from 15kW/m2 to 45kW/m2.

8. A process as claimed in claim 6 or claim 7, in which the duration of the exposure of the slices to the near-IR radiation is in the range of from 90 to 140 seconds.

9. A process as claimed in any one of claims 1 to 8, in which the exposure to near-IR radiation consists of exposing the slices to the radiation emitted by a heating element operated at a temperature of not less than 16000C.

10. A process as claimed in any one of claims 1 to 9, in which the baking further comprises a drying step subsequent to the exposure to near-IR radiation, the drying step comprising heating the slices in hot air.

11. A process as claimed in claim 10, in which the temperature of the hot air and the time during which the slices reside therein are so selected that the moisture content of the slices is reduced by said drying step to the said value of not more than 3% by weight, based on the total weight of the baked slices.

12. A process as claimed in any one of claims 9 to 11, in which the moisture content of the slices is reduced by said near-IR treatment to not more than 40% by weight, based on the total weight of the slices immediately after said near-IR treatment, the moisture content being further reduced in said drying step.

13. A process as claimed in any one of claims 10 to 12, in which said drying step comprises heating the slices in hot air at a temperature of not less than 1200C for a period of up to five minutes and further heating the slices in hot air at a temperature of from 80 to 1300C for a period of up to fifteen minutes.

14. A process as claimed in any one of claims 9 to 13, in which the fat content of the slices immediately before the drying step is from 1.75 to 20% by weight based on the total weight of the slices.

15. A process as claimed in any one of claims 1 to 14, in which the fat content of the vegetable snack product is not more than 25% by weight, based on the total weight of the product.

16. A process as claimed in claim 15, in which the fat content of the vegetable snack product is from 3 to 25% by weight based on the total weight of the product.

17. A process as claimed in claim 16, in which the fat content of the vegetable snack product is from 8 to 19% by weight, based on the total weight of the product.

18. A process as claimed in any one of claims 1 to 17, in which the moisture content of the vegetable snack product is not more than 2% by weight, based on the total weight of the product.

19. A process for the manufacture of a vegetable snack product substantially as described herein.

20. A vegetable snack product obtained by a process according to any one of claims 1 to 19.

21. An apparatus for use in the manufacture of a vegetable snack product, the apparatus comprising: cutting means for cutting the vegetables to obtain slices of vegetable; oil applying means for applying oil to at least one surface of the slices; oven means arranged downstream of said oil applying means, said oven comprising at least one radiant heating element having an operating temperature of not less than 16000C; and dehydrating means for further reducing the moisture content of the slices.

22. An apparatus as claimed in claim 21, wherein the operating temperature of the or each radiant heating element is at least 20000C.

23. An apparatus for the manufacture of a lowerfat snack product, the apparatus being substantially as described herein with reference to any of Figs. 1 to 4.