Abstract:
A method of de-oiling potato slices, which have been coated in oil, the steps of the method including providing a plurality of potato slices that were pre-treated in oil; and randomly feeding the potato slices onto an elongate longitudinal conveyor which is permeable to oil, water and air. Further, the method includes spraying water downwardly and upwardly onto the plurality of potato slices on the conveyor to displace and lift surface oil from the potato slices. Then, directing air blades to blow a mixture of oil and water from the potato slices as these move along the conveyor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is divisional of U.S. application Ser. No. 13/982,468 filed Oct. 9, 2013, which is a 371 National Stage Application claiming priority to PCT Application No. PCT/EP2012/051346 filed Jan. 27, 2012, which claims priority to Great Britain Application No. 1101607.8 filed Jan. 31, 2011, now GB Patent No. 2481469 issued Feb. 13, 2013, the technical disclosures of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
     Technical Field 
       [0002]    This invention relates to an apparatus and method for de-oiling potato slices in the manufacture of low oil potato chips. 
         [0003]    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. 
         [0004]    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&#39;s expectation for the particular product or class of products purchased. 
         [0005]    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 5 wt %, 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. 
         [0006]    WO-A-2008/011489 and WO-A-2009/091674 in the name of Frito-Lay Trading Company GmbH disclose processes for making a healthy snack food. In those processes, a snack food is made so as to have an appearance and taste similar to conventional fried snack products, such as a potato chip. The potato slices are subjected to a sequence of steps which avoids frying of the slices in oil, and the result is a low fat potato chip. 
         [0007]    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. 
         [0008]    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. 
         [0009]    Subsequent to the lipophilic preconditioning step an oil removal step is employed. The oil removal step is disclosed as being performed using a variety of different wet methods, which may, for example, use at least one of the following: a steam blancher; a perforated rotating drum; washing in a hot or cold water bath; pressurised water jets; water knives; air knives; air atomised water nozzles; a mist of fine droplets of water; superheated steam or nitrogen; or centrifugal oil removal. It is disclosed that the most preferred embodiment uses a water spray comprising a mist of fine droplets of water. 
         [0010]    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. 
         [0011]    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. 
         [0012]    There is accordingly still a need for an apparatus and method for efficiently and reliably manufacturing, in a cost effective manner, a low fat potato chip which has not been fried but has organoleptic properties, in combination with the visual appearance, of a conventional fried potato chip. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention accordingly provides an apparatus for de-oiling potato slices, the apparatus comprising an elongate longitudinal conveyor having an upstream end and a downstream end, the conveyor being permeable to oil, water and air and being adapted to convey potato slices on the conveyor, a water spray station located towards the upstream end and a plurality of air-blower stations located in succession downstream of the water spray station, the water spray station comprising upper and lower water spray units adapted to spray water downwardly and upwardly, respectively, towards the conveyor, and each air-blower station comprising upper and lower air knife units adapted to direct an air blade downwardly and upwardly, respectively, towards the conveyor. 
         [0014]    The present invention further provides a method of de-oiling potato slices which have been coated in oil, the method comprising the steps of:
       (a) providing a plurality of potato slices, each slice having been pretreated in oil;   (b) randomly feeding the potato slices onto an elongate longitudinal conveyor which is permeable to oil, water and air;   (c) spraying water downwardly and upwardly from respective upper and lower water spray units onto the plurality of potato slices on the conveyor to cause the water to displace and lift surface oil on the potato slices; and   (d) thereafter directing upper and lower air blades downwardly and upwardly, respectively, onto the plurality of potato slices on the conveyor to cause the air blades to blow a mixture of oil and water from the potato slices, wherein the air blades comprise a plurality of pairs of upper and lower air blades spaced along the conveyor.       
 
         [0019]    Preferred features are defined in the dependent claims. 
         [0020]    The present inventors have found that the provision of such a sequence of specific de-oiler elements and steps, and the avoidance of steam treatment during de-oiling, can provide a resultant potato chip, produced by the lipophilic preconditioning and microwave explosive dehydration steps discussed above, which not only has low oil but also has the combination of flavour, organoleptic properties and shelf life in a non-fried potato chip which is equal or superior in consumer acceptance to conventional fried potato chips. In particular, the invention uses water and air to de-oil the potato slices, whereas the known use of steam de-oiling was found to cause oxidation of potato lipids which reduced the achievement of both the desired flavour and long shelf life. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0022]      FIG. 1  is a schematic side view of an apparatus for de-oiling potato slices, prior to microwave cooking, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    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 present invention is illustrated in  FIG. 1 . 
         [0024]    A primary endless belt conveyor  2  having a substantially horizontal orientation is provided. An inlet end of the conveyor  2  communicates with an exit of an oil flume  4  (illustrated schematically) comprising a lipophilic preconditioning unit for the potato slices  6 . The conveyor  2  carries a succession of the potato slices  6  on its upper surface  8 . The potato slices  6  have been randomly delivered onto the conveyor  2 . The potato slices  6  are delivered onto the conveyor  2  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  6  are stacked one upon the other on the conveyor  2 . This substantially provides a monolayer of potato slices  6  across the length and width of the conveyor  2 . 
         [0025]    The potato slices  6  typically have a thickness of 1 to 2.5 mm, more typically about 1.3 mm (51 thousandths of an inch). 
         [0026]    The potato slices  6  have been pre-treated in oil in the lipophilic preconditioning process and initially, prior to the de-oiling step, have about 30 to 45 wt % surface oil, typically about 40 wt % surface oil based on the dry weight of the final potato chip produced from the potato slice  6 . 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. 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. 
         [0027]    The conveyor  2  has a translational speed of from 0.1 to 0.5 m/second, typically about 0.2 m/second. As the potato slices  6  are carried on the upper surface of the primary conveyor  2 , air is blown downwardly onto the potato slices  6  in a continuous manner at a primary air-blower station  18 . The velocity of the air is typically from 30 to 60 metres per second, more typically from 40 to 50 metres per second, optionally from 45 to 50 metres per second. The primary air-blower station  18  comprises a set of a plurality of primary air knives  10 ,  12  which are mounted above the primary conveyor  2 . In the embodiment, two longitudinally spaced air knives  10 ,  12  are provided. Each of the air knives  10 ,  12  typically has an air exit aperture  14  extending along the length of the air knife  10 ,  12 , which extends transversely across the conveyor  2 , for generating a downwardly-directed air blade  16  extending across the width of the conveyor  2 . The air exit aperture  14  may have a width of from 0.5 to 1.5 mm, optionally 0.75 to 1.25 mm, further optionally about 1 mm. Each air knife  10 ,  12  is located so that a distance from the air exit aperture  14  to the upper surface  8  of the conveyor  2  carrying the potato slices  6  is from 20 to 40 mm, optionally 25 to 35 mm, further optionally about 30 mm. 
         [0028]    The air knives  10 ,  12  generate downwardly directed parallel air blades  16 , spaced in the direction of movement of the potato slices  6  along the conveyor  2 , and act to blow excess surface oil on the potato slices  6  back into an oil supply for the lipophilic preconditioning apparatus. The air blades  16  most typically have an air velocity of 48 m/second. 
         [0029]    For example, the excess oil removed by the air blades  16  is blown downwardly through the conveyor  2 , and is captured by an oil capture device  20  located thereunder. The conveyor  2  is permeable to the oil and typically comprises an open mesh structure, for example comprised of a stainless steel balanced spiral wire mesh belt. 
         [0030]    The air knives  10 ,  12  are parallel and longitudinally separated by a distance of, for example, a distance of from 100 to 300 mm, typically about 150 mm, so that each potato slice  6  is sequentially impacted by plural air blades  16  during the passage of the potato slice  6  through the primary air-blower station  18 . Alternatively, the air knives  10 ,  12  may be separated by a distance which is less than a typical dimension of a potato chip, for example a distance of less than 50 mm, such as 30 to 40 mm, so that each potato slice  6  is simultaneously impacted by plural air blades  16  during at least a portion of the passage of the potato slice  6  through the primary air-blower station  18 . Optionally, the air knives  10 ,  12  are inclined rearwardly so that the displaced oil is directed rearwardly into the oil capture device  20 , which enhances oil capture. 
         [0031]    After this preliminary step of blowing off excess surface oil with air blades, the conveyor  2  feeds the potato slices  6  to a de-oiler unit  21 . The de-oiler unit  21  includes a second de-oiler belt conveyor  22  which, similar to conveyor  2 , is an endless belt mounted substantially horizontally and has a belt speed of from 0.1 to 0.5 m/second, typically about 0.2 m/second. The conveyor  22  is also permeable to oil and water, and comprises a similar open mesh structure as conveyor  2 , for example a stainless steel balanced spiral wire mesh belt. The de-oiler conveyor  22  conveys the potato slices  6  from an upstream end  24  to a downstream end  26  through a succession of de-oiling stations. 
         [0032]    A first de-oiling station  28 , located relatively upstream along the conveyor  22 , comprises a water spray station  30  which sprays water onto the potato slices  6  which are carried on the upper surface  32  of the conveyor  22 . The water is sprayed both downwardly from an upper water spray device  38 , forming an upper spray  39 , and upwardly from a lower water spray device  40 , forming a lower spray  41 . Typically, in each water-spray device  38 ,  40  a plurality of water pressure nozzles is provided across the width of the conveyor  22 . Typically, the water exits of the water spray devices  38 ,  40  are located a distance of from 50 to 150 mm, optionally 75 to 125 mm, further optionally about 100 mm, from the conveyor upper surface  32  carrying the potato slices  6 . 
         [0033]    At the water spray station  30 , water is sprayed onto both upper and lower major surfaces  34 ,  36  of each of the potato slices  6 . The water spray impacts on the upper and lower surfaces  34 ,  36  of the potato slices  6  and acts to displace and lift surface oil from the surfaces of the slice  6 . 
         [0034]    A typical water feed rate from each of the upper and lower water devices  38 ,  40  is from 3 to 5 kilograms of water per minute, optionally from 4 to 4.5 litres of water per minute, most typically 4.2 litres/minute, for a typical potato slice throughput of 250 kilograms per hour, i.e. from 0.72 to 1.2 litres of water per hour per kg of potato slices per hour, optionally from 0.96 to 1.08 litres of water per hour per kg of potato slices per hour. 
         [0035]    After this initial surface oil lifting step using water, a succession of pairs of oppositely directed secondary air knives, and directed towards each other, is employed to remove the lifted oil, mixed together with the residual water, from the surfaces  34 .  36  of the potato slices  6 . In the embodiment, three successive sets  42 ,  44 ,  46  of upper and lower air knives are employed, which sets  42 ,  44 ,  46  are located in a mutually spaced configuration extending along a portion of the length of the conveyor  22  downstream of the water spray station  30 . 
         [0036]    Accordingly, there are plural parallel sets  42 ,  44 ,  46  of upper and lower secondary air knives mounted above and below the conveyor  22  which are adapted to provide high velocity air, as a narrow blade-like flow extending across the width of the conveyor  22 , with the high velocity air blade blowing the water and oil mixture from the surfaces  34 ,  36  of the potato slices  6 . The velocity of the air is typically from 30 to 60 metres per second. The water and oil mixture which has been blown off the slices falls downwardly into a base  60  of the de-oiler unit for removal and reuse or recycling. The air blades produced from the sets  42 ,  44 ,  46  of upper and lower air knives are parallel. 
         [0037]    A first air knife set  42  comprises upper and lower air knives  48 ,  50  each of which is arranged to blow an air blade  52 ,  54  at a high velocity onto the upper or lower surface  34 ,  36 , respectively, of the potato slices  6  on the conveyor  6 . For these air knives  48 ,  50  the air velocity may be from 30 to 40 metres per second, optionally from 32 to 37 metres per second. Typically, the upper air knife  48  has an air blade velocity of 34 m/second and the lower air knife  50  has an air blade velocity of 35 m/second. 
         [0038]    A second air knife set  44  comprises upper and lower air knives  56 ,  58  each of which is arranged to blow an air blade  62 ,  64  at a high velocity onto the upper or lower surface  34 ,  36 , respectively, of the potato slices  6 . For these air knives  56 ,  58  the air velocity may be from 40 to 50 metres per second, optionally from 45 to 50 metres per second. Typically, the upper air knife  56  has an air blade velocity of 47 m/second and the lower air knife  58  has an air blade velocity of 47 m/second. 
         [0039]    A third air knife set  46  comprises upper and lower air knives  66 ,  68  each of which is arranged to blow an air blade  70 ,  72  at a high velocity onto the upper or lower surface  34 ,  36 , respectively, of the potato slices  6 . For these air knives  66 ,  68  the air velocity may be from 40 to 50 metres per second, optionally from 45 to 50 metres per second. Typically, the upper air knife  66  has an air blade velocity of 46 m/second and the lower air knife  68  has a velocity of 47 m/second. 
         [0040]    The use of a plurality of sequential successive pairs of oppositely directed air knives mounted both above and below the conveyor  22  in the de-oiler unit provides a greater degree of control in achieving a desired weight % of oil in the de-oiled potato slices  6  leaving the de-oiler unit  21 . 
         [0041]    For each of the air knife sets  42 ,  44 ,  46 , a typical distance from the respective upper or lower air knife exit aperture  74 ,  76  to the upper surface  32  of the conveyor  22  carrying the potato slices  6  is from 20 to 40 mm, optionally 25 to 35 mm, further optionally about 30 mm. Each of the air knives  48 ,  50 ,  56 ,  58 ,  66 ,  68  has an exit aperture  74 ,  76  extending along the length of the air knife  48 ,  50 ,  56 ,  58 ,  66 ,  68 , which exit aperture  74 ,  76  extends transversely across the conveyor  22 , for generating an air blade  52 ,  54 ,  62 ,  64 ,  70 ,  72  extending across the width of the conveyor  22 . The air exit apertures  74 ,  76  may have a width of from 0.5 to 1.5 mm, optionally 0.75 to 1.25 mm, further optionally about 1 mm. 
         [0042]    Since the air knife sets  42 ,  44 ,  46  blow air upwardly as well as downwardly, in order to avoid the potato slices  6  being blown off the conveyor  22  a longitudinally oriented hold-down belt  80  is located above the conveyor  22  in the vicinity of the air knife sets  42 ,  44 ,  46 . The potato slices  6  are conveyed between the lower conveyor  22  and the upper hold-down belt  80  and are held in position as they are conveyed successively past the air knife sets  42 ,  44 ,  46 . The hold-down belt  80  is typically undriven, but it may alternatively be driven so as to assist the conveyor  22 . 
         [0043]    In the illustrated embodiment, there are three sets of air knives  42 ,  44 ,  46  downstream of the water spray station  30 . In other embodiments a larger number of air knife pairs is provided, which can provide enhanced uniformity of oil content of the de-oiled potato slices. In contrast, since the air knives  10 ,  12  blow air only downwardly, a hold-down belt is not required. The potato slices  6  are agitated by the downwardly blown air from the air knives  10 ,  12 , which agitation assists removal of free surface oil, but the slices remain on the conveyor  2 . 
         [0044]    The final oil percent amount in the de-oiled potato slices  6  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 wt % water content, of the final cooked and dried potato chip after microwave explosive dehydration and final drying. 
         [0045]    In modifications to the illustrated embodiment, a single conveyor may be used instead of the combination of a primary conveyor and a de-oiler conveyor, and/or the number of air knives and/or water spray stations may be varied.