GB2125270A

GB2125270A - Method of processing rice

Info

Publication number: GB2125270A
Application number: GB08322409A
Authority: GB
Inventors: Donald William Bursill
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-08-20
Filing date: 1983-08-19
Publication date: 1984-03-07
Also published as: AU1808883A; GB8322409D0

Abstract

A "dry" method of preprocessing rice to produce a quick cooking rice involves cooking the rice substantially by direct heat or radiant heat at a temperature of between 350 DEG C to 500 DEG C for a period of time between 35 seconds and 10 seconds. The rice (5) is preferably heated by radiant heat from a heating element (3) as the rice is transported on a thermally non-conductive conveyor belt (20). <IMAGE>

Description

SPECIFICATION Method of processing rice The present invention relates to a method and apparatus for pre-processing rice to produce a quick cooking rice. In particular, the invention is directed to a method and apparatus for preprocessing rice by cooking the rice at a higher temperature for a short period of time by either direct contact or radiant heating.

Generally, untreated rice requires cooking for twenty to thirty minutes to render the same soft and palatable. For untreated brown rice, the cooking time is even longer. Many methods of preprocessing rice have been devised in order to produce a quick cooking rice. Nearly all of these methods rely on heat treatment of the rice. The methods can be classified loosely as "wet" and "dry" methods of pre-processing. In the "wet" methods, such as disclosed in U.S. Patents Nos.

2,438,939; 2,733,147; 2,740,719; 2,828,209 and 3,879,566, the rice grains are heated in the presence of an aqueous solution. This method is time consuming however, and involves a loss of valuable rice starch and produces a waste water pollution problem. The soaking of the rice in the water involves the use of excess water which invariably leads to a dissolving of rice starch into the water not only lowering the nutritional value of the rice but also resulting in the production of a starchy water effluent which must be disposed.

Similar methods using steam sprays are disclosed in U.S. Patents Nos. 2,937,946 and 4,385,074.

Such techniques require large amounts of hot water and thus consume a large amount of energy.

In the "dry" methods the raw rice grains are heated to produce numerous small cracks or fissures extending inwardly from the grain surfaces to, or nearly to, the grain centres. As a result, when the treated grains are subsequently cooked, moisture penetrates rapidly to the interior of each grain through the cracks or fissures, and the grain centres are cooked to the desired soft palatable condition without any substantial amount of surface overcooking in a period which is only a fraction of that required to cook the untreated rice grains. It is critical in such known methods of pre-processing rice by heat treatment that excessive heating be avoided. In the method of U.S.Patent No. 3,532,508, the time and temperature of pre-heating varies from ten seconds at 2500C to 30 minutes at 1 400C. It is stated that too high a temperature may impart an undesirable colour or taste to the sterilised rice.

Similarly, in the method of U.S. Patent No.

2,696,158, the rice is heated to a temperature between 11 00F to 2800 F. The maximum temperature is restricted as the patent states that excessive heating, as manifested by too high a final temperature, is to be avoided as it results in undue breakage of the grains. In the present invention however, the rice grains are cooked at a much higher temperature with favourable results.

Thus, unlike the methods of U.S. Patents Nos.

3,532,508 and 2,696,1 58 in which the rice is merely heated during the pre-treatment, the rice grains are actually cooked by the method of the present invention.

There are known methods of pre-processing rice to produce a quick cooking rice which use higher temperatures approaching those used in the present invention. For example, Australian Patent No. 244,945 discloses a method in which the rice is heated by an air stream at a temperature of 2050C to 31500 for a period of ten to forty seconds. Australian Patent Application No. 80141/82 discloses a similar method wherein the temperature of the hot air is between 4000C and 6000C. However, a serious disadvantage of these prior art methods, as well as the method disclosed in U.S. Patent No. 2,992,921, is that the methods are inherently inefficient as regards energy consumption.Since air is a very bad conductor of heat, the air must be heated to approximately 6000C to obtain a rice temperature of 150"C. Extra heat must be generated in order to heat the whole volume of air, and such extra heat together with the large area over which it is dissipated, gives rise to fire safety problems.

Moreover, the implementation of the method requires a large structure having a series of pipes and tubes for the hot air streams. The cost and inefficiency of the method and its apparatus are reflected in a less economical output. As a result, rice produced by such a method has a retail price substantially higher than that of ordinary untreated rice.

U.S. Patents Nos. 2,505,325 and 2,808,333 disclose methods in which the rice grains are heated to such an extent during the pre-treatment that they are cooked. In the method of the former patent, the rice grains are heated in a stream of hot gas of a temperature between 6500F to 1 2000F for a period of time less than a minute.

Although a gas stream of high temperature is used, the rice reaches a maximum temperature of only 3500F. In the method of the latter patent, the rice grains are heated in a stream of hot air at a temperature of 3000F to 5000F for a period of from 30 to 60 seconds. The method however is effective only for parboiled rice. Although these known methods disclose the step of cooking the rice during pre-treatment, the convection heating by which the cooking is achieved is inefficient and increases the cost of the processed rice. A simpler alternative of cooking the rice on a heated metallic plate has been found to be unsuitable as the rice grains are burnt by such high temperatures.

A further disadvantage of prior art methods using streams of hot air is that they are not entirely suitable for brown rice. As a high air temperature is required to achieve a suitable temperature of the rice grains, the husks of the rice grains are burnt. These husks would otherwise give the brown rice its characteristics.

It is an object of the present invention to overcome, or substantially ameliorate, the above described disadvantages by providing an improved method of pre-processing rice to produce a quick cooking rice.

According to the present invention, there is provided a method of pre-processing rice to produce a quick cooking rice, said method comprising the step of cooking said rice by direct heat or by radiant heat at a temperature of between 3500C to 5000C for a period of between 35 seconds to 10 seconds. Preferably, the rice grains are cooked on a thermally non-conductive surface.

Typically, the rice is heated at a temperature of approximately 4000 C.

In the preferred embodiment, the rice is cooked as it is transported along a non-metallic conveyor belt by heat radiated from a heating element placed over the conveyor belt. Metallic belts should be avoided as they will burn the rice grains; synthetic heat-resistant conveyor belts are preferred. Alternatively, a heating element may be placed below a portion of the non-metallic conveyor belt to heat the conveyor belt such that the rice grains being conveyed are cooked by direct contact with the heated conveyor belt. To achieve the required non-conductive yet heat resistant surface, a conveyor belt of KEVLAR material is preferred. The rice grains are agitated while they are being transported along the conveyor belt so that they are cooked uniformally.

The method of the present invention is very efficient as regards the consumption of energy as most of the heat produced is absorbed directly by the rice grains. Accordingly, only a short cooking time is required. Moreover, the apparatus required to implement the method is uncomplicated and may be constructed at low cost.

By way of example, a preferred embodiment of the invention will now be described with reference to the drawing, which is a schematic elevational view of apparatus for pre-processing rice.

As illustrated in the drawing, rice grains 5 are fed through a vibrating chute 10 onto a conveyor belt 20. The vibration of the chute 10 spreads the rice grains out in a single layer, or at most two or three layers of grain. If required, a gate 1 5 can be included to ensure that the rice is spread to a single layer thickness, although this is not essential. The conveyor belt is constructed from thermally non-conductive, yet heat resistant material. It will be understood by those skilied in the art that the material need not be 100% nonconductive, i.e. totally insulative; the belt need only be non-conductive to a substantial extent.

Further, the belt need only be heat resistant at the temperatures used, i.e. up to approximately 6000 C. KEVLAR material is suitable for the present invention.

The rice grains 5 are conveyed under, and close to, an elongated heating element 30 which radiates heat directly onto the rice grains. The period of time for which the grain is heated can be varied by adjusting the conveyor speed. The rice is heated at a temperature of 3500C to 5000C for a period of time of 10 to 35 seconds; obviously, the longer period is used at the lower temperature.

Typically, the rice is heated to a temperature of approximately 4000C for approximately 20 seconds, depending on the type of rice. Such treatment results in the cooking of the rice grains.

In addition to, or in substitution for, the heating element 30, a hot plate 40 can be placed under the conveyor belt 20, or incorporated in the conveyor belt 20, to heat the rice grains directly from below. The heating of the rice causes tiny cracks in the grains. When the rice is later cooked, the cracks convey heat directly to the centre of the rice grains thereby reducing the cooking time required for the rice. The rice grains can however be used directly in certain dishes as they have been precooked.

After the heating process, the rice grains are conveyed to an output station 50 for subsequent cooling. If cooled in water, nutrients can be added to the water, the nutrients clinging to the surface of the grains after they have been washed. After cooling, the rice is ready for packaging.

In the method of the present invention, the heat generated is conveyed directly by contact or by radiation to the rice grains. Accordingly, less heat is lost and the efficiency of the method is increased.

The foregoing describes only one embodiment of the present invention, and modifications, obvious to those skilled in the art, may be made thereto without departing from the scope of the invention as defined in the following claims. For example, the conveyor 20 can be replaced by an inclined vibrating feeder having a heating element thereabove. In this embodiment, the rice grains are heated while being transported along the feeding chute.

Claims

1. A method of pre-processing rice to produce a quick cooking rice, said method comprising the step of cooking said rice by direct heat or by radiant heat at a temperature of between 3500C to 5000C for a period between 35 seconds to 10 seconds.

2. A method as claimed in claim 1 wherein said rice is cooked by radiant heat on a thermally nonconductive surface as it is transported by conveying means under a heat radiating element.

3. A method as claimed in claim 2 wherein said rice is agitated during the cooking step.

4. A method as claimed in claim 1 wherein said rice is cooked on a thermally non-conductive surface of conveying means as it is transported thereon, said surface being of KEVLAR material and said conveying means comprising a heating element.

5. A method of pre-processing rice to produce a quick cooking rice, said method comprising the step of cooking said rice on a thermally nonconductive surface by direct heat or by radiant heat at a temperature of between 350"C to 5000C for a period between 35 seconds to 10 seconds.

6. Precooked rice prepared by the method as claimed in claim 1.

7. Apparatus for performing the method of claim 1, said apparatus comprising conveying means having a non-metallic surface for transporting rice grains, a heating element disposed above at least a portion of said conveying means carrying said grains, said heating element being at a pre-determined height and of pre-determined length in the direction of travel such that rice on said conveying means is heated at a temperature of between 350 C and 5000C for a period of 35 to 10 seconds as it passes under said heating element.

8. Apparatus as claimed in claim 7, further comprising barrier means positioned above said conveying means before said heating element for spreading rice grains along the surface of the conveying means to less than three layers thick.

9. Apparatus as claimed in claim 7, wherein said conveying means is a conveyor belt of KEVLAR material.

10. Apparatus for performing the method of claim 1, said apparatus comprising conveying means having a non-metallic surface for transporting rice grains, said conveying means having a heating element juxtaposed and in contact with a portion of said conveying means carrying said grains, said heating element being of a pre-determined length in the direction of travel of the grains such that the rice grains are heated on said conveying means at a temperature of between 350 C to 500"C for a period of between 35 seconds and 10 seconds.

11. A method of pre-processing rice substantially as hereinbefore described with reference to the accompanying drawing.

12. Apparatus for pre-processing rice substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawing.