Abstract:
Objects are sorted according to specific gravity by illuminating the objects with near-infrared light with different wavelengths. Measurement of the light absorbed by each object at the different wavelengths permits a dry matter content of the object to be determined. Specific gravity can then be determined using a predetermined correlation between dry matter content and specific gravity. A sorting mechanism responsive to determination of specific gravity by the controller separates the food objects into at least two different groups corresponding to different specific gravity.

Description:
This application claims priority to U.S. Provisional Application No. 60/864,627, filed Nov. 7, 2006. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a system for rapidly and non-destructively determining specific gravity and sorting food objects according to their food processing requirements. More particularly, the present invention relates to a method and a system of determining the specific gravity of potato French fry strips. The system will allow for the sorting of the fry strips for processing according to customer specifications by specific gravity measurement at several locations in a processing line. 
     BACKGROUND 
     Specific gravity or the solids content of potatoes is an important determinant of harvest quality. A processing potato must have a high specific gravity and low sugar content. A high specific gravity results in french fries that have a more desirable mealy texture and flavour, are crisp and absorb less oil during frying compared to fries from potatoes with a lower dry matter content. Determining the specific gravity is necessary because it indicates how much water must be evaporated from the potato during the dehydration process prior to frying the strips. It is actually a measure of the dry matter or “solids” in the potato. High specific gravity potatoes make the best French fries and dehydrated potato products. In practice, this attribute of a tuber is an indicator of maturation that the industry uses as a reference to judge fry quality, baking characteristics and storability. More importantly the specific gravity measurements reflect environmental factors and cultural management procedures that were made during the production season. In addition, the distribution of starch or dry matter, sugar content, types of sugars and distribution, internal cell structures, tuber size and shape, tuber defects such as growth cracks and hollow heart can also influence specific gravity measurements. Improper sampling and methods of determinations could mislead specific gravity measurements and result in improper equipment settings on the processing line. This results in product quality losses for the processor. 
     There is no product or device in existence that can perform automatic monitoring of specific gravity on the french fry processing line. Specific gravity is currently determined by a crude manual method. A sample of tubers and several tubs of water (with salt added to make brine at different specific gravities) are used. The weight in air versus the weight in water method is another of the common methods of specific gravity determinations. Selected sample units are first weighed in air and then the same unit is re-weighed suspended in water. Specific gravity can then be calculated using the following formula:
 
Specific gravity=Weight in air/(Weight in air−Weight in water)
 
     This is a time-consuming testing method that does not allow for quick and accurate sampling and therefore it does not allow the processor to set the fryers and drier machines in real time. Both sampling methods are also not very accurate as contamination of the brine barrel with dirt, potato starch etc. and contamination of the weighing water occurs after only a few samples have been tested. 
     The other common method of measuring specific gravity is to use a potato hydrometer. The hydrometer consists of a float with the neck graduated to specific gravity readings. A basket containing the sample is hung beneath the float and the whole assembly placed in water. After some time the float remains steady and the specific gravity is read from where the water level is on the neck of the hydrometer. The higher the specific gravity, the deeper the hydrometer will be in the water. 
     The disadvantage of this method is that the hydrometer is calibrated to a fixed weight of potatoes in the basket and therefore the sample placed in the basket must be exactly this specified weight. 
     It can be time consuming finding tubers of the right size to make the exact weight, and also the hydrometer can bob up and down for some time before a reading can be made. If the hydrometer is knocked about, the chart of specific gravity readings inside the neck can be moved, thereby resulting in totally inaccurate readings. Hence, this method, although commonly used, is not thought to be very accurate. A further disadvantage is the sample size: the hydrometer is limited to the amount specified in the basket and therefore is not a very representative sample. 
     SUMMARY OF THE INVENTION 
     The proposed concept described herein generally comprises a Near Infra-Red Spectroscopic device that measures the specific gravity of french fry strips in the manufacturing plant. Near infra-red spectrophotometry (NIR) is widely used in the food processing industry for assessing various quality characteristics of food products because it is a rapid, not destructive method that can be adapted for use on processing lines. As described herein, a NIR device has been devised to sample fry strips on the french fry processing line and to allow for the subsequent sorting of the fries by specific gravity to assist the processor in maximizing end-product quality and reducing waste. 
     According to one aspect of the present invention there is provided a sorting system for sorting food objects according to specific gravity in a processing line, the system comprising: 
     a conveyor arranged to carry objects therealong; 
     a near-infrared light source arranged to illuminate objects on the conveyor with near-infrared light in which a first portion of the light has a wavelength readily absorbed by water content in tissues of the object and a second portion of the light has a wavelength absorbed by the water content in tissues of the object less than the first portion; 
     a detector for measuring light absorbed by the object at the different wavelengths of near-infrared light; and 
     a controller arranged to:
         i) determine dry matter content using the light absorbed by the object as measured by the detector; and   ii) determine specific gravity using a predetermined relationship between dry matter content and specific gravity.       

     According to a second aspect of the present invention there is provided a method of sorting food objects according to specific gravity, the method comprising: 
     illuminating the food objects with near-infrared light in which a first portion of the light has a wavelength readily absorbed by water content in tissues of the object and a second portion of the light has a wavelength less absorbed by the water content in tissues of the object; 
     measuring light absorbed by each food object at the different wavelengths of near-infrared light; and 
     determining a dry matter content of each food object using the measured light absorbed by the food object; and 
     determining a specific gravity of each food object using a predetermined relationship between dry matter content and specific gravity. 
     The method preferably includes separating the food objects into at least two different groups corresponding to different ranges of specific gravity. 
     Preferably the second portion of the near-infrared light has a wavelength readily absorbed by a dry matter portion of the object. More particularly, the second portion of the near-infrared light may have a wavelength readily absorbed by a dry matter portion of a food object comprising a potato product, for example a french fry strip. 
     As described in the preferred embodiment herein, near-infrared light sources are arranged over the conveyor in which at least a component of the light has a wavelength more sensitive to water absorption than other components of the light. The detector measures the different wavelengths of near-infrared light reflected by the object. A controller is arranged to determine dry matter content in the fry strips by using near infrared (NIR) measurements along with a predetermined calibration of the instrument. The changes in the near-infrared measurements are correlated to the dry matter content of the potato material. The controller is then further arranged to determine specific gravity using a predetermined relationship between dry matter content and specific gravity. A computer controlled system will make a rapid determination of the best route for the fry to travel to produce the best end quality result. Various adjunct driers may be employed to further dry the strips prior to reinstating them onto the conveyor for movement to the frying station. 
     The conveyor is preferably arranged to carry cut fries therealong in a french fry processing line. The fries are preferably sorted by the controller and a sorting mechanism after a cutting operation of the processing line which cuts potatoes into fries. 
     There may be provided a surface dryer after the cutting operation and before the near-infrared light source to remove surface moisture on the fries. 
     The controller and the sorting mechanism may be located after a fryer in the processing line to sort between fries having a specific gravity within an acceptable range from fries having a specific gravity outside of the acceptable range. 
     Alternatively or additionally, a controller and a sorting mechanism may be located before a fryer in the processing line to sort between fries having a specific gravity within an acceptable range from fries having a specific gravity outside of the range. 
     The fries outside of the acceptable range may be forwarded to a processing line for a different food object. 
     The acceptable range preferably includes an upper limit wherein fries are outside of the acceptable range if a specific gravity thereof is above the upper limit. 
     The acceptable range preferably also includes a lower limit wherein fries are outside of the acceptable range if a specific gravity thereof is below the lower limit. 
     When the controller and the sorting mechanism sort the fries between those within an acceptable range of specific gravity and those outside of the range, the controller and the sorting mechanism preferably sort the fries within the acceptable range between fries to be sent directly to a fryer and fries to be sent to a dryer before the fryer. 
     The controller and the sorting mechanism may be provided after the dryer for sorting the fries between an acceptable range to be sent directly to the fryer and fries outside of the acceptable range and arranged to be sent to a second dryer. 
     The controller and the sorting mechanism may sort the fries after the dryer between fries within an acceptable specific gravity range to be sent to the fryer and fries outside the range arranged to be sent to a reject area. 
     The sorting mechanism may be actuated by a timer corresponding to a duration for a fry to be displaced by the conveyor from the detector to the sorting mechanism. 
     The sorting system may be provided in combination with a processing line comprising a plurality of parallel conveyors each having a near-infrared light source, a detector, a controller and a sorting mechanism associated therewith. 
     The sorting mechanism is preferably responsive to determination of specific gravity by the controller and arranged to separate the food objects into at least two different groups corresponding to different ranges of specific gravity. 
     The detector may be arranged to measure a length of each food object. In this instance, the sorting mechanism may also be responsive to length determination of the food objects such that the sorting mechanism is arranged to separate the food objects into at least two different groups corresponding to different ranges of lengths. 
     The detector is preferably arranged to receive multiple reflections along a length of a food object as the food object is displaced along the conveyor. In this instance, the controller may be arranged to identify regions of differing specific gravity along a length of a given food object. 
     The controller is preferably arranged to identify regions of the given food object having a specific gravity which is lower than a remainder of the given food object. 
     There may be provided a cutter arranged to remove regions of the given food object having a specific gravity within an unacceptable range of specific gravity. 
     The wavelength of the near-infrared light from the near-infrared light source is preferably adjustable to correspond to different biotypes of a given food object. 
     One embodiment of the invention will now be described in conjunction with the accompanying drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall schematic view of a food processing line which incorporates the sorting system according to the present invention. 
         FIG. 2  is a schematic representation of a scanning portion of the sorting system. 
         FIG. 3  is a schematic representation of a plurality of sorting systems in parallel with one another for use in the processing line according to  FIG. 1 . 
     
    
    
     In the drawings like characters of reference indicate corresponding parts in the different figures. 
     DETAILED DESCRIPTION 
     Referring to the accompanying figures there is illustrated a sorting system generally indicated by reference numeral  10 . The system  10  is particularly suited for sorting food objects according to specific gravity. In the exemplary embodiment, the sorting system  10  is applied to a food processing line for sorting food objects, for example french fries, for sorting the fries according to quantities of denser tissues, for example higher dry matter tissues, to determine specific gravity by its correlation to content of water in the tissues versus the content of dry matter in the tissues. 
     A food processing line  12  is shown in  FIG. 1  in which potatoes are first cut into fries at a cutter  14 . The cutter  14  comprises a series of wet knives so that the resulting cut fries include surface moisture thereon upon exiting the cutter  14 . A surface dryer or air curtain may be required  16  to dry surface moisture, which may affect subsequent scanning operations, so as to improve the effectiveness of the sorting system. 
     The sorting system generally comprises a scanner  17  for scanning the object and a sorter  50  responsive to the scanner  17 . Scanning for denser dry matter tissues in the fries is accomplished using a scanner  17  comprising a near-infrared (NIR) light source  18  which emits NIR light at specific wave lengths and a detector  20  for receiving reflected NIR light back and thereby determine tissue content by assessing what portion of and what wavelengths of the NIR light from the source  18  are absorbed by the food object and which pertain to the water content of the food object. 
     In the processing line  12  a first scan takes place after the surface dryer or air curtain  16  to initially assess if the cut fries should proceed on to the next step of the process comprising the blancher  22  or if the food objects should be discarded into a reject area  24  or sorted to be sent through various adjunct driers for further drying. Fries will be sent to the reject area if the determined specific gravity thereof falls well outside of the acceptable range which would result in the desired quality of finished products. Depending on if the specific gravity is considered high or low, the fries will be passed through the blancher quickly or more slowly. 
     The scanner  17  is also arranged to detect start and end points of each fry as it passing along the processing line  12  such that the length of each fry is determined. The sorter  50  responsive to the scanner  17  can thus also be arranged to redirect a fry to the reject area  24  if the length of the fry is outside of a prescribed range of lengths which are considered acceptable, for example if the fry length is below a prescribed lower length limit. 
     In the illustrated embodiment an additional scanner  17  is placed after the blancher  22  to determine what additional path through the processing line  12  the fry should take to result in a desirable finished product. The scanner  17  after the blancher commands the respective sorter  50  associated therewith to divide the product into subsequent paths  26 . For saving floor space, the different paths  26  can be stacked vertically if desired. 
     The product is directed to the first path if the determined specific gravity is above the upper prescribed limit for the processing system. Accordingly the product is redirected to an upper limit bin  28  to be subsequently forwarded to a different processing line for other potato products having differing specific gravity requirements for product quality. 
     Similarly another path  26  receives fries redirected thereto if the specific gravity of the fries is determined to be less than a lower limit for acceptable product quality. This path leads to a lower limit bin  30  to be forwarded on similarly to the fries in the upper limit bin  28 . 
     Another path  26  includes fries thereon which have been redirected to the path if their specific gravity is determined to be within an optimum range to be fed directly to a fryer  32  or through an existing high throughput dryer  33  of the processing line before being further sorted or sent to the fryer  32 . 
     The fries are redirected to another of the paths  26  if its specific gravity is below the optimum range to be sent directly to the fryer but is still above the lower prescribed limit of the processing line. In this instance the fries are redirected down the conveyor to a suitable auxiliary dryer  34  which dries the fries to remove excess moisture content and thereby increase the specific gravity thereof to the acceptable range to be sent to the fryer or subsequent scanner. More than one such path to the dryer may be provided if further classification is desired between fries which require only some drying to reach the acceptable range versus some fries which require considerable drying to reach the acceptable range to be sent to the fryer. 
     In the illustrated embodiment, a further scanner  17  is provided after the dryers  34  when a single drying path is provided so that the scanner after the dryer commands the respective sorter  50  associated therewith to separate the fries between those which have already reached the acceptable limit to be sent to the fryer  32  from those which require further drying. The latter are accordingly sent to a secondary dryer  36  before reaching the acceptable specific gravity range for being subsequently forwarded back to the fryer  32 . 
     Before final processing in the fryer  32 , the scanner  17  and sorter  50  just before the fryer may also be arranged to identify regions within individual ones of the fries which have a specific gravity which differs from, for example which is much lower than, an average specific gravity of the remainder of the fry. This is accomplished by taking multiple readings of light reflection from the fry along its length and determining specific gravity at each reading location along the length of the fry. An auxiliary cutter  37  can be operated responsive to the determination of regions of the fries having specific gravity outside of the acceptable range to cut or trim those regions from the remainder. The trimmed parts are then discarded while the remainder continues on to the fryer  32 . 
     A further scanner and sorting system may be positioned after the fryer and before the freezer to sort out those fries that still do not meet the requisite quality parameters specified. Any combination of the sorting and scanning systems may be used by individual processing plants and the units will be custom built to best suit the needs of the processor&#39;s clients. 
     Turning now more particularly to  FIG. 2 , the scanner will now be described in further detail. Each scanner  17  is used in cooperation with a conveyor  38  having suitable guides  40  supported in relation thereto to guide fries so that they are aligned in a longitudinal direction of conveying movement of the conveyor  38 . The NIR light source  18  is mounted above the conveyor adjacent one end thereof for directing the NIR light downwardly onto the fries situated on the conveyor  38 . The source  18  generally comprises two lasers  42  for emitting NIR light at two respective wavelengths. One of the lasers  42  emits light which has a wavelength which is substantially absorbed by the water content of the tissues of the french fries. The other laser  42  emits light that is less absorbed by the water content and is absorbed by the dry matter of the object and is used as a reference. 
     The detector  20  of the scanner  17  is also mounted above the conveyor in a common housing with the two lasers of the NIR light source  18 . A lens of the detector is positioned close to the object for catching reflections  44  of NIR light from the object. A suitable detector within an integrating sphere  46  is connected to a data acquisition system which is controlled by a processor  48  which controls operations of the system. Multiple scans are taken along the length of the fry as it passes under the source  18  and detector  20 . Multiple systems will be required to assess the specific gravity of all the fries traveling in all the conveyor lanes. Multiple lasers and detectors may be positioned inside common housing to reduce the size of the scanning equipment. 
     The processor determines the dry matter content and accordingly the specific gravity by using the intensity of the reflected light at different wavelengths. The specific gravity is determined using a pre-determined relationship between dry matter content and specific gravity. 
     The sorter  50 , or sorting mechanism, is mounted in association with each scanner  17  in proximity to the respective conveyor  38  for redirecting each fry to the appropriate one of the paths  26  subsequent to scanning the fry using the NIR source  18  and detector  20 . The sorter  50  generally comprises a chute  52  which is pivotally mounted adjacent one end of the conveyor. The processor  48  controls the pivotal position of the chute  52  between one of several positions, each comprising the chute  52  being connected in communication between the end of the conveyor  38  and a respective one of the paths  26 . The processor  48  includes an integral timer for controlling position of the chute  52  of the sorting mechanism so that the chute is responsive to the determined specific gravity of a fry only once the respective fry reaches the chute  52 . 
     As described herein, the scanner  17  and sorter  50  are useful at various locations as a sorting system within the processing line  12 . In the exemplary embodiment scanning and sorting may take place after the cutter  14  once the surface is dry, after the blancher  22  and prior to the fryer  32 , after some drying operation to determine if more drying is needed, and finally after the fryer  32  to assess if the desired quality has been reached before the product is released from the processing line  12 . 
     In use the processing line  12  may comprise a plurality of parallel lines, for example up to forty main lines, which initially begin as a single common feed  60  directed by baffles  62  into the individual parallel lines. A sorting system  10  comprising the scanner  17  and sorter  50  are provided in association with each of the separate parallel lines. Each of the sorters  50  may however redirect the fries to several common paths so that all rejected product is redirected to a common reject area  24 , all product requiring further drying is sent to a common dryer  34  and all product within the acceptable limits are sent to a common fryer  32 . 
     The technology described herein using NIR is a non-invasive method of determining specific gravity of french fry strips during processing. The system uses spectroscopic methods of analysis to examine the water and plant tissue content of the fry strip. This information is used to make a determination for sorting the fries into different treatment streams and through adjunct driers if required. The sorting equipment, which is part of the system, is controlled by the specific gravity readings generated. The computer makes a determination on each fry strip and moves the fries that require more drying to an adjunct drier. One or more adjunct driers and conveyor systems may be used at the discretion of the processing plant. Fry strips that require further drying prior to moving them back into the stream for frying are put through one of the adjunct driers prior to moving to the fryer. Fries that do not require drying are moved directly to the fryer. Fries that are over or under specific gravity standard requirements go into a separate bin to be recycled into other potato products such as hash browns or dehydrated potato flakes. As many sorting streams as required by the processing plant can be added to the system and accommodated by the specific gravity monitoring system. Each system will be custom built to suit the needs of the plant. 
     Near-infra red (NIR) instrumentation has been configured to take multiple measurements at specific wavelengths of light reflected from the French fry surface using an integrating sphere. The optical measurements obtained are indicators of the absorption of the NIR light wavelengths and can be used in an algorithm to determine the specific gravity. 
     The specific gravity monitor (SGM) uses NIR illumination on a sample and measures the reflected light energy with a photodiode detector operating in the NIR region. The sample is illuminated, in turn, by two different NIR wavelengths. The first gets more absorbed by the water content in the potato whereas the second is used as a reference and does not get absorbed as much by the water content, but rather is readily reflected by the object. The detector is fixed to the port of an integrating sphere. The latter offers the benefit to capture light reflected from different angles and to average the signal over the inner reflecting surface of the sphere. 
     The SGM device is under controlled through the USB port of a computer. Commands are provided to perform automatically a sequence of measurements. Once completed, the data is stored as a record in a data file. A calculation of the total mass (weight) of the fry strips passing through the system will also be provided with the data file. 
     Once the individual fry strip has been analyzed the computer will determine which sorting treatment to apply. Some fry strips will continue down the main conveyer to the fryer. Other fry strips will be sorted by a mechanical sorting method and moved to another conveyor belt for movement to an adjunct drier. Multiple driers or drier settings can then be used to modify the dry matter and moisture content of the fry strips prior to allowing them to move to the fryer. Determination of the specific gravity may take place in several locations depending on the requirements of the processing plant. For example, four possible locations for specific gravity monitoring devices and associated sorting equipment are immediately after the water knives have cut the strips, after the blancher or prior to the adjunct drier, after the drier and after the fryer. Sorting at each of these locations reduces the variability in product quality. 
     Commands from the computer will be communicated to PCL controllers to modify the resident times and temperatures of the driers and fryers. This will allow the processor to more precisely control the quality of the fry strips exiting the processing line. The computer can be programmed to automatically adjust the driers and fryers based on the average quality of the product coming into the system. 
     
       
         
               
               
             
           
               
                   
               
               
                 Functional Characteristics - Fry 
                   
               
               
                 Strips 
                 Benefits 
               
               
                   
               
             
             
               
                 Device senses specific gravity across 
                 Allows the processor to set the driers 
               
               
                 length of fry strip (6 to 10 readings per 
                 and fryers on line to improve quality of 
               
               
                 strip in milliseconds) 
                 final product 
               
               
                 Device is not in direct contact with the 
                 Cleanliness is maintained, device does 
               
               
                 product 
                 not need frequent cleaning and is not 
               
               
                   
                 fouled by product or debris 
               
               
                 Variation in air humidity in the plant 
                 Moisture in the air will not interfere with 
               
               
                 does not affect the device 
                 accuracy of readings 
               
               
                 Moisture on the surface of the fries 
                 As the fries leave the water knives 
               
               
                 may be removed by a small air jet from 
                 excess moisture may need to be 
               
               
                 an air curtain or surface drier 
                 removed from the fry surface so that 
               
               
                   
                 the water does not affect the accuracy 
               
               
                   
                 of the specific gravity readings 
               
               
                 The device can read at faster than the 
                 The conveyor belt is moving at 70 ft per 
               
               
                 rate of travel of the individual fries on 
                 min but the device requires only 
               
               
                 the conveyor belt. 
                 nanoseconds to take multiple reading 
               
               
                   
                 and make a sorting determination 
               
               
                 Sorting the fry strips can easily be 
                 Sorting the strips into separate streams 
               
               
                 accomplished after they have been 
                 for different treatment by the driers or 
               
               
                 analysed by the specific gravity monitor 
                 fryers decreased the variability of the end product 
               
               
                 Removal of potato strips with specific 
                 The ability to remove strips with very 
               
               
                 gravity readings that are too high or too 
                 high or very low specific gravity will 
               
               
                 low to be processed into French fries 
                 greatly enhance the overall quality of 
               
               
                 will be directed into a separate bin for 
                 the French fry product overall and will 
               
               
                 use in other potato products 
                 result in price premiums to the processor 
               
               
                 In addition to measuring specific gravity 
                 The ability to assess mass will allow 
               
               
                 the device will also provide an accurate 
                 the processor to carefully monitor 
               
               
                 running total mass (weight) 
                 product losses due to moisture loss - 
               
               
                 measurement to the processor to 
                 these measurements will help in 
               
               
                 indicate total mass of product at any 
                 making purchasing decisions and in 
               
               
                 given point requested. 
                 setting product prices. The mass 
               
               
                   
                 measurements may also allow the 
               
               
                   
                 processor to more accurately control oil 
               
               
                   
                 inputs, and make decisions on other 
               
               
                   
                 quality parameters in real time. 
               
               
                   
               
             
          
         
       
     
     Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.