WO2001028686A1

WO2001028686A1 - Process and apparatus for de-hulling and splitting lentils

Info

Publication number: WO2001028686A1
Application number: PCT/CA2000/001203
Authority: WO
Inventors: Cy Ross
Original assignee: Cy Ross
Priority date: 1999-10-15
Filing date: 2000-10-13
Publication date: 2001-04-26
Also published as: AU7894500A; AU778710B2; CA2386243A1

Abstract

Lentils are fed in the form of a sheet of a single thickness of lentils to the gap (8) of a pair of opposed, cylindrical, slightly gapped, downwardly rotating rollers (9) ('chaffers'). Each chaffer has an elastic, resilient, circumferential surface layer (12) having a Shore A durometer hardness of 60-85. The rollers are gapped and rotated at a speed and speed differential operative to remove the hull when de-hulling and to split the kernels when splitting. De-hulling is conducted at ambient temperature and the resulting kernels are dried and heated for splitting.

Description

PROCESS AND APPARATUS FOR DE-HULLING AND SPLITTING LENTILS

FIELD OF THE INVENTION The present invention relates to a process and apparatus for de-hulling and splitting lentils.

BACKGROUND OF THE INVENTION A lentil is a form of pea which comprises an internal kernel having an external, thin, fibrous hull or husk. The kernel is generally shaped like a football and has a plane of weakness along its midline so that it may be separated down the middle into two halves. In the trade, the hulled kernels are commonly referred to as "wholes" or "footballs" and the separated kernel halves are referred to as "splits". Hulled splits provide a widely marketed food source. They are rich in proteins and can be quickly cooked by boiling in water. It is desirable to split the wholes to conserve energy used in cooking the lentils. In Western Canada lentils are commonly de-hulled and split using a sequence of two machines referred to as a "huller" and a "splitter".

The huller comprises a stack of disc-shaped stones, slightly spaced apart vertically and contained in a close-fitting drum or housing. The stones are rotated within the drum by a common drive. The bottom outlet from the drum is choked as required to control the retention time. The lentils are fed in at the top of the drum. As they slowly work their way down to the outlet, the hulls are loosened and removed by frictional contact with the stones, drum wall and other lentils. The cleaned or hulled wholes are then fed into the splitter. This unit comprises a pair of stacked, conically-shaped stones, slightly spaced apart vertically, contained in a close-fitting housing. The stones are rotated at different speeds. In reaction to the regime of frictional forces to which they are subjected as they pass through the splitter, the wholes are sub-divided into splits. This commercially applied equipment and procedure is characterized by certain shortcomings. More particularly:

• Too many of the lentils may be insufficiently de-hulled. This is particularly a problem with large lentils having flat or irregular surfaces. As a result, the end product of hulled splits may be contaminated with too high a proportion of hull material;

• Too many of the hulled kernels may become chipped, with the result that part of the kernel is lost as fragments with the chaff; and

• Too many of the splits may be chipped with consequent losses of valuable kernel material. Typically, these prior art commercial operations will have losses of kernel material in the order of 20 - 30% and contamination of the end product with hull material will often exceed the international standard of 1.5% maximum hull content.

The present invention has as objectives:

• reducing fragmentation or chipping of the wholes and splits;

• improving the efficiency of removing hulls to thereby reduce the proportion of hull material in the final product;

• increasing the production of splits as the final product; and

• providing a system which is able to successfully process a variety of lentil types, particularly large lentils having irregular surfaces.

SUMMARY OF THE INVENTION In accordance with the invention, I have combined apparatus and process steps and conditions to achieve improved recovery and purity of hulled splits. More particularly, the invention involves:

• Providing a pair of opposed, cylindrical, slightly gapped, downwardly rotating rollers referred to as 'chaffers'. Each chaffer has a rubber-like or elastic, resilient, circumferential surface layer. The rubber-like layer is preferably formed of polymer or elastomer and preferably has a Shore A durometer hardness of about 60 - 85, more preferably about 65 - 85. This range has been found to provide good adherence to the hull. If the hardness is less than about Shore A 60, the feed submerges too deeply in the chaffer surface layer and de-hulling suffers. If the hardness is greater than about Shore A 85, increased chipping of the lentils results. The chaffer surfaces are spaced apart, preferably to form a gap just less than one split in width. Preferably the gap spacing is about 20 - 30/1000 of an inch, optimally about 24/1000" for large calibre lentil. The gap spacing provides minimal chipping during splitting. The chaffers are rotated at different speeds to provide a frictional shearing effect adequate to remove the hull when de-hulling and to split the kernels when splitting. In addition the chaffers are rotated at speeds selected to provide adequate retention time to achieve the desired quality of de-hulling and splitting. Preferably the chaffers are operated at a rotational speed differential in the range of about 56 - 61 %, more preferably 58 - 61 %. If the differential is lower than about 56%, shearing is less adequate for de-hulling and splitting. If it is higher than 61%, retention time is short and de- hulling and splitting results suffer. In addition, the feed exit velocity from the chaffers becomes excessive and further chipping occurs. Optimally, I operate a pair of 15" diameter chaffers at 675 - 685 rpm for one chaffer and 1060 - 1090 rpm, for the other, respectively;

Providing a feed means for supplying the lentils or kernels to the top end of the chaffer gap in the form of a laterally extending sheet of single lentils or kernels (that is, the sheet is only one lentil or kernel in thickness) - if the feed is stacked in layers during feeding, chipping is increased; • Providing an exit chute, at the bottom of the chaffer gap, which is adapted to direct the product into a container with a minimum of chipping. More particularly the chute may be a flat, curved tube that has top and bottom walls that are closely spaced to contain and guide the emitted product while minimizing zig-zag movements that can lead to chipping. The kernels leave the differentially rotating chaffers at high velocity and at an angle. It is therefore desirable to channel and guide them to the container with a chute designed to minimize fragmentation; and

• Passing the lentils and whole kernels in sequence through chaffers in a two stage process of de-hulling and splitting at controlled temperatures. Preferably the same pair of chaffers are used for each of the two stages. In the first stage, the lentils, at ambient temperature, preferably at a temperature of about -10°C to +27°C, most preferably -10 to 20°C, are passed through the chaffers to remove about 80 - 90% of the hull material and produce about 97% cleaned wholes and about 3% splits. If the temperature of the feed in the first stage is less than about minus 10°C, hull separation deteriorates. If the temperature is greater than about 27°C, de- hulling suffers and a greater quantity of splits is produced. The product is then dried and heated, for example in a grain dryer, preferably to about 30 - 41 °C to weaken the adhesiveness of the splits forming the wholes. If the temperature of the wholes fed to splitting is less than about 30°C, there is a decrease in the yield of splits. If the temperature of the wholes is greater than about 41 °C, the meat of the kernels is degraded. The heated wholes are then passed through the chaffers for splitting. As a result of processing the lentils in this way, one can recover 85 - 88% of the original kernel material or meat in the form of splits with a hull content less than 1.5%. The purity of the splits product is in the order of 99%. The losses of kernel material has been reduced to about 12 - 14%, compared to the prior art system losses of about 20 -30%. In one aspect, the invention is directed to a process comprising:

• de-hulling lentils at a temperature of about -10°C to 27°C by feeding them through the gap of a pair of spaced apart, opposed, downwardly rotating chaffers having elastomeric surface layers and being rotated at different speeds so that they are operative to apply adequate frictional shearing to de-hull substantially all of the lentils to produce substantially clean "wholes" or kernels;

• drying and heating the cleaned wholes to a temperature of about 30 - 41°C; and

• splitting the dried heated wholes by feeding them through the gap of a pair of spaced apart, opposed, downwardly rotating chaffers having elastomeric surface layers and being rotated at different speeds so that they are operative to apply adequate frictional

shearing so as to split substantially all of the wholes to produce

substantially clean splits. In another aspect, the invention is directed to an assembly comprising:

• a pair of cylindrical, driven, gapped, downwardly rotating rollers having elastomer or polymer surface layers having a Shore A durometer hardness of about 60 - 85, the rollers being rotated at different speeds so that the differential is about 58 - 61 %, the rollers being spaced apart about 20 - 30/1000";

• flat means for feeding lentils or lentil wholes to the gap between the rollers as a single unit layer - that is, the layer is formed of lentils (or wholes) that are not stacked one on another; and

• curved flat tube means for receiving hulled lentil wholes or splits issuing from the gap and closely containing them while delivering them to storage container means. Broadly stated the invention in one form comprises a method for de- hulling lentils, each comprising a kernel covered by a hull, the kernel consisting of a pair of united halves or splits, to produce whole kernels comprising: passing lentils, at ambient temperature through a pair of opposed, cylindrical, gapped, downwardly rotating, driven rollers, each having an elastic, resilient circumferential surface layer formed of material having a Shore A durometer hardness in the range 60 to 85, the rollers being rotated at different speeds selected to provide sufficient frictional shearing so that the major portion of the lentil hulls is removed to produce hulled whole kernels. Broadly stated, the invention in another form comprises a method for de-hulling lentils, each comprising a kernel covered by a hull, the kernel consisting of a pair of united halves or 'splits', and splitting the hulled kernel into splits, comprising passing lentils at ambient temperature through a pair of opposed, cylindrical, gapped, downwardly rotating, driven rollers, each having an elastic, resilient circumferential surface layer, the rollers being rotated at different speeds, the Shore A durometer hardness of the roller surface layers, the gap between the rollers, the roller speeds and their differential in speed being collectively operative so as to substantially remove the lentil hulls and produce hulled kernels; heating and drying the kernels to produce kernels having a temperature in the range 30°C to 41 °C; and passing the produced kernels having a temperature of 30°C to 41 °C through a pair of opposed, cylindrical, gapped, downwardly rotating, driven rollers, each having an elastic, resilient circumferential surface layer, the rollers being rotated at different speeds, the Shore A durometer hardness of the roller surface layers, the gap between the rollers, the roller speeds and their differential in speed being collectively operative so as to split the kernel into splits. And in another form the invention comprises apparatus for de-hulling lentils, each comprising a kernel covered by a hull, to produce whole kernels, comprising a pair of opposed, cylindrical, gapped, downwardly rotatable rollers; each roller having an elastic, resilient circumferential surface layer formed of material having a Shore A durometer hardness in the range of 60 - 85; the rollers having a gap spacing in the range 20/1000 to 30/1000 of an inch; and means for individually rotating each roller so that the rollers may be operated at a rotational speed differential.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic side view showing the feed hopper and tray, chaffers, exit tube and product container; Figure 2 is an expanded view of part of Figure 1 ; Figure 3 is a top plan view of the chaffers and their drive assemblies; and Figure 4 is a perspective view of the assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will now be described in connection with a test run at optimum conditions. In accordance with the Figures, a feed hopper 1 was provided for feeding lentils (in a first stage) and hulled wholes (in a second stage) onto a wide, downwardly angled tray 2. The tray 2 comprised a bottom wall 3 and side walls 4. A plurality of upstanding dividers 5 sub-divided the upper end of the tray 2 into parallel channels 6 extending part of the length of the tray. The upper end of the tray 2 was open but its lower end was closed in by a top wall 7 to form a flat tube. The tray 2 extended between the hopper 1 and the gap 8 formed between the chaffers 9. The widths of the hopper 1 and tray 2 were substantially equal to the length of the gap 8. The hopper fed the lentils to the tray as a train or sheet of feed, one feed unit thick, moving down the channels 6. Otherwise stated, a feed means, comprising the hopper 1 and tray 2, was provided for feeding feed in the form of a sheet, substantially one feed unit

thick, to the chaffer gap 8 along its length. The chaffers 9 were a pair of cylindrical hollow steel drums 11 , each

coated with an elastomeric surface layer 12. The steel drums 11 had an O.D. of 15" and length of 24". Each was coated with a layer 12 of polyurethane, about 0.5 inches thick. The polymer was obtained from Rubberworld Industries Inc. of Edmonton, Alberta, Canada. The elastomer was bonded to the steel. It had a Shore A hardness of about 65. The chaffers 9 were evenly spaced apart .024" to form the gap 8. The chaffers 9 were horizontally and rotatably mounted in a frame 14. Conventional belt and sprocket assemblies 15, driven by hydraulic motors 16, separately rotated each of the chaffers 9 at a variable selected speed. The chaffers were operated at 675-685 and 1060 - 1090 rpm respectively to provide a speed differential of about 59.5%. An exit chute 20 extended along and downwardly from the gap 8 to the storage container 21 or other delivery point. The exit chute 20 was a flat tube extending the length of the gap 8. It comprised top, bottom and side walls 22, 23 and 24. The top and bottom walls 22, 23 were spaced apart 5/8 inches. The chute 20 was curved and had a length of about 14". In the first stage or pass of the process, de-hulling, the lentils, at a temperature of 19 - 22°C, were supplied to the gap 8 as a feed layer with the lentils close together but only one unit thick. After passing through the chaffers 9, the chaff and kernel chips were separated by screening. The product, hulled wholes, was then heated in a grain dryer (not shown) to raise the feed temperature to 38 - 40°C. The heated feed was then fed through the same chaffers 9 in the same way as the original lentils. Following are the results of the run: De-hulling:

• yield of hulled whole kernels - 75.1 %

• yield of unhulled whole kernels - 17.9%

• yield of hulled splits - 0.68%

• yield of unhulled splits - 0.05%

• losses (hulls and chips) - 6.22% Splitting:

• yield of hulled wholes - 17.1 % • yield of unhulled wholes -4.3%

• yield of hulled splits - 72%

• yield of unhulled splits - 0.9%

• losses (hulls and chips) - 5.7%. A number of runs using the assembly shown have been carried out at varying conditions. The following observations have been made, comparing them to the optimum run described:

• In de-hulling, with increasing temperature of the feed, the recovery of hulled wholes decreased and the recovery and purity of splits decreased;

• When the speed differential was 55% the percentage of hulled wholes was less and when the speed differential was 65% the percentage of hulled wholes decreased; • If the gap was 0.022", hull and chip losses increased, if the gap was 0.030", purity of the final product decreased;

• If the splitting temperature was 30°C, split yield decreased and if the temperature was greater than 41 °C, kernel degradation was noted.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS

FOLLOWS: 1. A method for de-hulling lentils, each comprising a kernel covered by a hull, the kernel consisting of a pair of united halves or splits, to produce whole kernels comprising: passing lentils, at ambient temperature, through a pair of opposed, cylindrical, gapped, downwardly rotating, driven rollers, each having an elastic, resilient circumferential surface layer formed of material having a Shore A durometer hardness in the range 60 to 85, the rollers being rotated at different speeds selected to provide sufficient frictional shearing so that the major portion of the lentil hulls is removed to produce hulled whole kernels.

2. The method as set forth in claim 1 wherein: the rollers are gapped to provide a gap spacing in the range 20/1000 to 30/1000 of an inch.

3. The method as set forth in claim 1 wherein: the rollers are operated at a rotational speed differential in the range 56 to 61%.

4. The method as set forth in claims 1 , 2 or 3 wherein: the lentils are at a temperature in the range minus 10°C to 27°C.

5. The method as set forth in claim 1 , 2 or 3 wherein: the roller surface layer Shore A durometer hardness is in the range 65

o 85.

6. The method as set forth in claim 1 , 2 or 3 wherein: the lentils are at a temperature in the range 10°C to 20°C; and the roller surface layer Shore A durometer hardness is in the range 65

to 85.

7. A method for de-hulling lentils, each comprising a kernel covered by a hull, the kernel consisting of a pair of united halves or 'splits', and splitting the hulled kernel into splits, comprising: passing lentils at ambient temperature through a pair of opposed, cylindrical, gapped, downwardly rotating, driven rollers, each having an elastic, resilient circumferential surface layer, the rollers being rotated at different speeds, the Shore A durometer hardness of the roller surface layers, the gap between the rollers, the roller speeds and their differential in speed being collectively operative so as to substantially remove the lentil hulls and

produce hulled kernels; heating and drying the kernels to produce kernels having a

temperature in the range 30°C to 41 °C; and passing the produced kernels having a temperature of 30°C to 41 °C through a pair of opposed, cylindrical, gapped, downwardly rotating, driven rollers, each having an elastic, resilient circumferential surface layer, the rollers being rotated at different speeds, the Shore A durometer hardness of the roller surface layers, the gap between the rollers, the roller speeds and their differential in speed being collectively operative so as to split the kernels into splits.

8. The method as set forth in claim 8 comprising: feeding the lentils to the gap between the rollers in the form of a sheet of lentils, said sheet being only one lentil thick; and feeding the hulled kernels to the gap between the rollers in the form of a sheet of kernels, said sheet being only one kernel thick.

9. The method as set forth in claim 7 or 8 wherein: the rollers have a Shore A durometer hardness in the range 60 to 85; the rollers are gapped to provide a gap spacing in the range 20/1000 to 30/1000 of an inch; and the rollers are operated at a rotational speed differential in the range 56 to 61%.

10. Apparatus for de-hulling lentils, each comprising a kernel covered by a hull, to produce whole kernels, comprising: a pair of opposed, cylindrical, gapped, downwardly rotatable rollers; each roller having an elastic, resilient circumferential surface layer

formed of material having a Shore A durometer hardness in the range of 60 - 85; the rollers having a gap in the range 20/1000 to 30/1000 of an inch; and means for individually rotating each roller so that the rollers may be operated at a rotational speed differential.

11. The apparatus as set forth in claim 10 comprising: means for feeding lentils along the length of the roller gap at its upper end in the form of a layer of lentils, one lentil in thickness.

12. The apparatus as set forth in claim 11 comprising: a curved, flat chute, having top, bottom and side walls and extending along the length of the gap at its lower end, for receiving hulled kernels and conveying them to a delivery point.