AU2002315059B2 - Milling rice process - Google Patents

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AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Milling rice process The following statement is a full description of this invention, including the best method of performing it known to us: Freehills Carter Smith Beadle MeIbourneWO4lBBS29 Pr[nted 9 December 2002 (14:07) page 2 Freehills Carter Smith Beadle Mel bourne%004188629 Printed 9 December 2002 (14:07) page 2 004183203 2 RICE MILLING PROCESS Technical Field This invention relates to a rice milling process and rice products produced by the process.

Background of the Invention Rice milling has been in widespread use for over one hundred years. Rice milling refers to processes leading to the production of whole grain rice. Brown or husked indica (long grain) rice is usually used as the feedstock for mills. However, Japonica or round grain rice is also widely used as a feedstock.

A typical rice milling process involves dehusking, followed by several stages of cleaning before the rice grain passes through polishing machines. Polishing involves rotation between the grain surfaces to remove the outer layers of the grain.

Most of the milling operations for rice are directed towards obtaining whole kernels.

The milling process typically includes grain size and colour sorting to enable a uniform clean product. The materials that are excluded in this sorting process are cracked, split, damaged and undersized rice kernels. The handling and storage of the excluded material leads to problems in a milling plant where there is generally little storage facility. The excluded material is usually disposed of in stockfeed products. These are sold at much lower prices than the whole kernel rice products that are used for human consumption. A relatively small quantity of whole rice kernels are milled or ground to produce rice flour and other divided rice product.

It would be desirable if the excluded material could be processed into products for human consumption or industrial products rather than stockfeed product.

Summary of the Invention This invention provides in one form a process of treating rice kernels excluded from a rice milling process comprising the steps of treating the excluded rice kernels to a first size separation stage, reducing in size by milling rice material larger than a first predetermined size, collecting rice material less than a second smaller predetermined size, collecting material intermediate in size between the first 004193203 3 and second predetermined sizes and further milling and separating the collected intermediate material based on particle size.

Preferably the milling is roll milling.

Preferably the roll milling is carried out in a four roller mill.

Preferably adjacent rollers in the roller mill rotate in opposite directions.

Preferably the first predetermined size is 0.5mm and the second predetermined size is 0.1mm.

The size separation is preferably carried out by a series of mesh sieves. The process can be adjusted by appropriate selection of sieve sizes to lead to fine or course grits as well as flour.

The sieves are usually arranged in the form of a vertically arranged array of trays. A commercial example is the equipment from Buhler AG known as the Square Plantsifter Novastar. The size separation of the material is carried out by a sieve stack of successively finer mesh sizes arranged in a sieve box. The size separated fractures are directed via channels in the sieve box. Suitable roll or roller mills are also supplied by this company.

Detailed Description of the Invention The invention will be further described by reference to the preferred embodiments in schematic flow diagram illustrated in Figures la and lb. These preferred embodiments are by way of example only and the present invention is not restricted to such equipment. Referring to this flow diagram, excluded rice kernel material is introduced at hopper 1 and the product then proceeds through multiple size separations and roll milling stages. A roll mill is size reducing equipment that has multiple rotating rollers. This milling stage reduction process is contrasted to the whole grain milling process described above for preparing rice kernels.

A preferred mill is a four roller miller. This machine is constructed for strength and rigidity and consists of two cast iron sides firmly braced together and mounted on a substantial one piece cast iron base. There are only fourteen parts of the frame which are subjected to stresses due to the pressure between the rolls.

These parts of the frame serve to hold together the bearing of the upper and lower 004193203 4 frames.

Roller mills have a vertical tension rod which supports the outer end of the lower roller bearing arm which is itself supported by the eccentric shaft. Driven pulleys are fixed to the spindle of the rolls which are bell shaped. The transmission of power and speed relationship between the two rolls is achieved usually by means of differential gears, with helical cut teeth running in an enclosed oil bath. Some rolls are fitted chain drives.

The roll surface is chilled and the depth of chill varies slightly. The original depth on a new roll is about 5 mm but reduced as the flutes wear. The roll may be refluted or recut. Rolls are set diagonally in the frame at an angle of 450 and run in opposite directions. The upper roll runs faster than the bottom roll.

Rolls are 250 mm in diameter and range from 610 mm to 1500 mm in length.

In the first sizing operation, 16 flutes are usually fitted with 320 mm diameter pulley, which is supplied on the feed roll driving spindle.

For the 2nd, 3rd, 4th and 5th sizing roller mills, the distributing worm is installed on the back feed. The feed plate is fitted above the front feed roll.

Reduction rolls are driven from the fast roll with a 250 mm on the feed roll driving spindle. The feed is on the back feed roll which runs at 32 rpm. The front feed rolls runs at 127 rpm when the main fast roll is running at 210 rpm.

The rolls do not run at equal speeds as this would merely flatten or crush the stock.

A shearing and scraping action is required on sizing rolls and a grinding action on reduction rolls and these are obtained by driving the upper roll appreciably faster than the lower roll. The differential is about 1.5 to 1.

Sizing rolls run at differential 2.5 to 1.

Fluting spiral on sizing rolls is usually 1 in 7, which means that the flute moves 1 inch around the roll circumference, for every 7 inches of axial length.

Camber of reduction rolls are machined in the form of a very shallow arc.

The camber in the diameter at the extreme ends is about .002 inch. The lower roll is ground dead level. Camber allows for roll expansion caused by heating. The main purpose is to counteract the slight deflection of the rolls under load.

004183203 As well as roll mills, other mills or forms of particle size reduction may be used. These include hammer mills and grinding apparatus. A comprehensive description of size reduction equipment is set out in chapter 20 of Perry's Chemical Engineer's Handbook 7 th Ed) McGraw Hill Int Eds.

The sizing, grading, dusting dressing are all sifting operations though their purposes and the means by which they are carried out are very different.

Sizing is the coarse separation that follows each roll. Its purpose is to separate the grit particles, after which the remaining stocks are sent to the next stage or to the branny stock after the last stage.

Grading is the separation of a single stock into two or more groups according to particle size. Rice flour dressing is the sifting out of the oversize particles from rice flour.

In each process the separations are made by particle size on a sieve of one kind or another, which allows small particles to pass through the apertures and overtails larger particles.

It is important that the amount of particle size of the troughs should be controllable. This demands the use not only of suitable types of sifting machinery but very accurate woven wire, nylon bolting cloth.

Bolting cloth is usually sold according to the number of threads per lineal inch. Cloths normally used range from 5 to 100 meshes per inch. Some cloths do not have the same thickness of thread for the same mesh, the thicker the thread, the smaller the apertures. Warp threads run lengthwise and weft threads run at right angles across the cloth. For accuracy, the warps are counted rather than the wefts when examining a cloth for grade.

The above described plant may be installed in an existing rice mill but may be also set up as a separate operation. In this latter case the excluded material would be sourced from various rice mills.

In operation there are many considerations to be taken into account: grade of rice stock to be processed; grades of product to be made; 004183203 6 size of plant, upon which, to a considerable extent the amount of surface to be allocated to all parts of the flow depends; types of machines to be used, for sizing, grading and dressing; to what extent grading is to be carried out.

Adjustments made on one machine or group of machines may extend their effects to many subsequent operations, and may considerably alter the characteristics of the products.

There are many human consumption type products able to be prepared from the rice materials from the present invention. The rice materials may be used in industrial processes.

As an example, the grits may be used for preparing rice crackers. A preferred rice grit is one having the majority by weight of the product in the particle size range of 0.1 to 0.5 mm. The products of the present invention may be used in a wide range of products intended for human consumption. For example, they may be used in rice chips or crackers as well as soups and pasta products. In these food applications the rice products of the present invention are combined with other ingredients. As can be seen by this example, the present invention is a means of value adding. The invention converts relatively low value material suitable for use as feed stock to a much higher value product useful for human consumption.

Since modifications within the spirit and scope of the invention may be readily effected by persons skilled in the art, it is to be understood that the invention is not limited to the particular embodiment described, by way of example, hereinabove.

Claims (6)

1. A process of treating rice kernels excluded from a rice milling process comprising the steps of treating the excluded rice kernels to a first size separation stage, reducing in size by milling rice material larger than a first predetermined size, collecting rice material less than a second smaller predetermined size, collecting material intermediate in size between the first and second predetermined sizes and further milling and separating the collected intermediate material based on particle size.

2. A process as defined in claim 1 wherein the milling is roll milling.

3. A process as defined in claim 2 wherein the roll milling is carried out in a four roller mill.

4. A process as defined in any one of claims I to 3 wherein the first predetermined size is A process as defined in any one of claims 1 to 4 wherein the second predetermined size is 0.1mm.

6. A process as defined in any one of claims 1 to 5 wherein the size separation is carried out by a series of mesh sieves.

7. Rice product produced by a process as defined in any one of claims 1 to 6. Qubera Pty Ltd By Freehills Carter Smith Beadle Registered Patent Attorneys for the Applicant 9 December 2002