MANUFACTURE OF LOW OIL SNACK FOOD

This invention relates to a method of removing oil from an 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 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, WO-A-2009/091674 and GB-A-248 I 469 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.

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 organoleptic 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 flavour and organoleptic 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:

i. spraying water onto the oil-coated surface of the food slice at a water mass flow rate of from 8 - 500 grams per m ² of the surface of the food slice to form a water-and-oil-containing layer on the food slice surface; and ii. applying at least one air jet 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 provides a 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 form a snack food.

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 therebetween;

b. feeding a plurality of oil-coated food slices along the 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 greater than 200% of the maximum thickness of the food slices;

c. spraying water onto oil-coated surfaces of the food slices to form a water-and- oil-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-and-oil-containing 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 air jet treatment at a particular air flow velocity can surprisingly achieve lower oil content in the resultant food slice. Also, the low oil can provide a combination of flavour, organoleptic properties 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 surface 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 invention is at least partly predicated on the finding by the present inventor that although some oil can be blown by air off the surface of an oil coated food slice, such as a potato slice, air blowing alone cannot remove sufficient oil at a practical air speed, because the food slice has "hard to remove" oil on its surface which cannot be removed solely by an air jet unless impractical, transonic air speeds (for example from Mach 0.8 to below Mach 1) 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 off the food slice surface using air jets. The air jets are controlled not only to remove the oil, but also to provide a low free water content in the food slices so that the food slices can be cooked by microwave cooking without arcing. 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 of from 6 to 18 wt%, preferably from 1 1 to 13 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 invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 schematically illustrates a potato slice to be de-oiled in 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;

Figure 3 is a schematic side view of an apparatus for de-oiling potato slices, prior to microwave cooking, for use in an embodiment of the method of the present invention; Figure 4 is a schematic plan view of a lower belt for use in belt assembly in an embodiment of the method of the present invention; and

Figure 5 is a schematic plan view of an upper belt for use in belt assembly in an embodiment of the method of the present invention.

Figure 1 schematically illustrates a potato slice 2 to be de-oiled in an embodiment of the method of the present invention. The potato slice 2 is coated with oil. The oil is present in a "hard 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 potato slices, the method of the invention may be employed to de-oil any food slices coated with surface oil. For example, the food slices may comprises slices of other vegetables, for example root vegetable such as carrot, parsnip, beetroot, sweet potato, etc or slices of dough-based products, which may include vegetable- and/or cereal-based dough. Figure 2 schematically illustrates the relationship between oil 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, d, 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, i.e. closer to the surface of the potato slice, such low velocity air is insufficient 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 mixture 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%, 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 from 5 to 8 wt%.

An embodiment of an apparatus for de-oiling potato slices, prior to 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 1 1 of the conveyor 10 communicates with an exit of an 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 2. The conveyor 10 has a translational speed of from 0.1 to 0.5 m/second, typically about 0.2 m/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 1 to 2 mm, more typically about 1.3 mm (51 thousandths of an inch).

The potato slices 2 have been pre-treated in oil in an oil-blanching step which 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 vvt% surface oil, typically about 40 wt% surface oil based on the dry 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 wt% 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, conventionally used for manufacturing potato chips. Alternatively the oil is any other vegetable oil, optionally at least one or a mixture of at least two of sunflower oil, rapeseed oil and olive oil. 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 the subsequent microwave cooking step, and has not been fried, as for a conventional potato chip.

The belt assembly 12 comprises an upper endless belt 16 and a lower endless belt 18, which define a product flow path 20 therebetween. 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 upper and lower endless 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 2.

The upper endless belt 16 comprises a plurality of interlinked metal links 26 having an open area of from 75 to 85% and a link depth of from 4 to 6 mm. Preferably, the open area is from 80 to 85% and the link depth is about 5 mm. The plurality of interlinked 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 mm. Preferably, the open area is from 65 to 70% and the link depth is about 6 mm. The plurality of interlinked metal links form a rectangular grid structure in the lower endless belt 18.

As the potato slices 2 are carried on the upper surface of the conveyor 10, water is sprayed from water spray nozzles 30 onto the potato slices 2 in a continuous manner at a water spray station 32 and 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 - 500 grams per m ² 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 water mass flow rate is from 40 - 80 grams per m ² of the surface of the potato slices 2.

At the air-blower station 34, at least one air jet 38 from an air jet nozzle 40 is applied, as an air knife, 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. The at least one air jet 38 blows at least a proportion of the water-and-oil-containing layer from the surface 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 substantially 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 from 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 ie the water spray treatment is from 40 to 95°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 jet treatment, 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 air jet treatment a bulk air flow is provided around the potato slices 2 to entrain dispersed droplets of water and oil within the bulk air flow to 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 shown) in at least one vacuum plenum 50 located in the vicinity of the potato slices 2. In the embodiment, plural vacuum plenums 50 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 example from -90 to -1 10 mbar. The or each port is typically located at a distance of from 3 to 25 mm, 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 by and retained within the specifically configured belt assembly 12 which not only holds the potato slices 2 against being blown off 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 oil-coated 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 blow 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, relative 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 upstream 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 when 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 sequentially, against the upper and lower surfaces 44, 46, respectively, of the potato slices 2.

The at least one air jet 38 is applied to the potato slices 2 when the potato slices 2 are in the product flow path and between the upper and lower endless belts 16, 18. The plurality of the air jets 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 jets 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 using 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 oil from oil-coated surfaces of the potato slices 2, the potato slices 2 are cooked, for example by microwave cooking, to form a snack food, in this embodiment potato chips. In the microwave cooking step, the bulk moisture content of the potato slices 2 is reduced from an average value of at least 75 wt%, typically about 80 wt%, based on the total weight of the potato slices 2 to an average bulk moisture content of from 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 provide, after the cooking step, an oil content on the cooked potato slices 2 of from 6 to 18 wt%, preferably from 1 1 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 from 5 to 8 wt%. The moisture content is then reduced further by finish drying, for example to a final moisture content for the potato slices of 2 +/- 0.5 wt% based on the dry weight of the potato chip.

The final oil percent amount in the de-oiled potato slices 2 is achieved by balancing the amount of water and the amount of air supplied. It is possible to 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 12.5 wt% oil +/- 2 wt% based on the dry weight, having 2 +/- 0.5 wt% water content, of the final cooked and dried potato chip after microwave explosive dehydration and final drying.

In modifications to the illustrated embodiment, the number of air knives and/or water spray stations may be varied.