JPH02227145A - Unhulled rice drying method - Google Patents

Abstract

PURPOSE:To dry unhulled rices within a short time without deteriorating the quality of the rices by radiating far infrared-ray within a temperature and duration range not to cause cracking of the rices to rices spread as a thin layer, cooling, and tempering, and repeating these processes. CONSTITUTION:Rices 15 is spread on a belt conveyer 4 to form a thin layer, irradiated with a far infrared-ray within a temperature range (e.g. 30-40 deg.C) and a duration range (e.g. 5 seconds to 1 minutes) not to cause cracking the rices from a far infrared-ray radiating heater 5, and then cooled and tempered on a belt conveyer 11. The far infrared ray irradiation and tempering are repeated. As a result, without causing deterioration of the rices (cracking and taste), drying the rices can be carried out within a short time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention heats harvested rice in the form of paddy under predetermined conditions, turns the tempering links over, and produces dried rice with less shell cracking and good flavor. The present invention relates to the drying method obtained.

(Prior art) There are two methods for drying harvested rice: one is to dry the ears of rice naturally outdoors without threshing, and the other is to force dry the rice in the form of paddy. Regarding the latter, there was a conventional method of drying using hot air.

(Problems to be Solved by the Invention) In the above case, rapid drying causes cracks in the rice inside, that is, cracks in the shell, and too high a temperature (40° C. or higher) causes a decrease in flavor. In addition, the surface layer of rice grains is covered with a waxy skin that does not allow moisture to pass through, and since moisture mainly evaporates from the germ, internal diffusion is the rate-limiting factor during forced drying. If drying continues without sufficient diffusion, there will be a large difference in moisture content between the surface and the inside of the rice, which will cause the rice to crack.

For this reason, after being heated for a predetermined period of time, it is left to cool to achieve uniformity through the diffusion of moisture. This operation is called "tempering" here.

Hot air drying is a method of passing hot air through the piled rice, but it is difficult to pass hot air uniformly through the rice, resulting in uneven temperature of the rice.

Since there is a limit to the drying temperature of paddy as mentioned above, in the case of hot air, the temperature of the highest part of the piled paddy must be kept within this limit, so the energy provided to the entire paddy is low, resulting in very long drying times.

In addition, in hot air drying, it is difficult to maintain the internal temperature as high as possible while keeping the surface layer temperature of the paddy below 40°C, and from this point of view as well, it is not possible to increase the drying rate.

Tempering is necessary even in hot air drying, and either this drying and tempering are repeated, or the drying time is long as described above, so the overall time is quite long.

In recent years, far-infrared irradiation has been used to dry various objects including foods, but it has not yet been established as a method for drying rice, and has not yet been put to practical use.

An object of the present invention is to provide a method for drying paddy in a short time without impairing the quality of rice (breakage, flavor).

(Means for Solving the Problems) As a result of intensive research to solve the above problems, the present inventors have found that by combining strong and uniform irradiation with far infrared rays and tempering links, the present inventors have developed a technology that is far more effective than conventional hot air. It has been discovered that a high drying speed can be obtained and high quality dried rice without shell cracking can be obtained.

The present invention was made based on the above discovery, and the gist of the invention is to spread rice in a thin layer, irradiate it with far infrared rays at a temperature and time range that does not cause the rice to crack, and then leave it to cool. This method of drying paddy consists of repeating far-infrared ray irradiation and tempering.

The present invention will be explained in detail below.

The moisture content of harvested paddy is generally 24 to 25% by weight (hereinafter referred to as
(% is weight), and depending on the climate, up to about 20% will dry naturally. In order to make rice with good shelf life, it is necessary to reduce the moisture content to about 15%.

In addition, considering the balance with other operations involved in rice harvesting, the allowable volume of drying equipment, etc., it is preferable that the drying speed be as fast as possible.The economically necessary moisture reduction rate is 0.5% or more per hour. , preferably 1.0% or more.

In order to make the forced drying part more compact, it is desirable to minimize the ratio of heating time to tempering time.

In order to obtain high-quality rice that dries to a predetermined moisture content at a predetermined rate and is free from cracking, it is necessary to adjust the irradiation intensity, time, and tempering conditions and time within appropriate ranges.

In the present invention, paddy is spread in a thin layer on, for example, a belt conveyor. The thickness of the layer is set to 1 in order to apply far infrared rays as uniformly as possible.
Far infrared rays are irradiated to this layer, which is preferably about 2 layers. As the far-infrared irradiation material, known materials such as those containing mullite, cordierite, zircon, alumina, zirconia, etc. as main components are used. A plate made of a pipe made of these materials with a heat source inserted in a rod shape or a metal plate such as aluminum, the heat source arranged between them, and the surface of the metal plate coated with far-infrared irradiation material by thermal spraying etc. The irradiation heater is made up of something like this.

The irradiation time may vary depending on the intensity of the far infrared rays, or may be short or economical, and is suitably 5 seconds to 1 minute. During this time, the temperature of the rice is brought to 30-40°C, preferably 33-37°C. When heating on a conveyor belt, the temperature increases gradually during irradiation or reaches this temperature range while in the irradiation zone. That is, the above temperature is the temperature at the end of irradiation, and the intensity and time of irradiation are selected so that the above temperature range is reached during irradiation. The temperature of paddy varies slightly between the inside and surface of a single paddy, as well as for each individual paddy, so here it is expressed as the overall average value.1For example, after irradiation, the paddy is immediately placed in a thermos flask to keep the temperature constant. If you measure at that point, you can get very accurate measurements.

Next, tempering is performed for 10 to 30 minutes.

This temperature is suitably within a range of 5 to 15° C. higher than the temperature after irradiation and the air temperature. During tempering, it is preferable to obtain adequate ventilation, which further accelerates the drying rate. After the tempering is completed, the far-infrared ray irradiation is performed again, and this far-infrared irradiation and tempering are repeated. The number of repetitions varies depending on these conditions, but −
15 to 50 times is appropriate for boat fishing.

The method of the present invention will be explained below by showing examples of specific apparatuses.

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention, and reference numeral 1 in the figure indicates a storage tank for raw material paddy, in which the amount to be processed for one time is stored. 2 is a switching damper, 3-1
Quantitative feeder 3 receives raw materials from storage tank 1 only when tank 1 is empty.
flow to. During drying operation, paddy is received from a hopper 12 and fed to a quantitative feeder 3, from which the paddy 15 is fed onto a bell converter 4 so as to have a constant width and a constant thickness (about 1 to 2 layers).

5 is a far-infrared radiation heater, which is controlled by a controller to keep the surface temperature at a constant value.

The speed of the bell controller 4 is constant, and the speed is determined so that the irradiation time of the rice grains is a predetermined value of 5 seconds to 1 minute. 6 is a cover. The paddy discharged from the bell converter 4 passes through a chute 7, enters a packet elevator 8, and then reaches a switching damper 9. 9 is normally in the direction of flowing toward the hopper IO side, and is switched to the storage tank 14 side after a certain period of time has passed after the raw material is supplied, that is, when a predetermined moisture content is reached. After the timer is activated, the water is discharged at 14 for a certain period of time and then switched to 10 bias again. lO is a hopper, 11
is a bellcon. The amount of paddy in the hopper 12 is controlled by operating the hopper 11 at a variable low speed or by interlocking the powder level meter attached to the hopper 12.

In addition, if the powder level meter at the bottom of hopper 12 indicates empty and a certain period of time has passed, the switching damper 2 will become a receiver from the hopper l, and when the powder level meter at the bottom of hopper l becomes empty, the receiver will be placed from the l again. becomes. 14 is a dry paddy storage tank. l, 11.
The storage capacity of 14 is approximately the same. Note that 13 is a blower, and in order to promote drying during tempering, 7.8.
Send wind to 10.

(Function) Far-infrared rays have high energy absorption efficiency on the surface of the rice, and since the energy is supplied to the inside, it is possible to uniformly and quickly raise the temperature inside the rice.

The moisture inside the rice moves quickly to the germ, which is the evaporation port.

Therefore, even when heating and tempering are repeated in the same way as hot air drying, it is possible to achieve more efficient drying than hot air drying in both the far infrared ray irradiation and tempering steps, and overall drying can be achieved in a shorter time than hot air drying. .

〔Example〕

Paddy was dried using the drying apparatus shown in FIG. The raw material used was paddy with a moisture content of 19%. In order to make the far infrared ray irradiation time 8 seconds, the amount charged in the Belcon 4 was approximately 150 times (approximately 400 kg) the amount retained on the Belcon 4. Adjusted the speed. As a result, the tempering time was approximately 20 minutes. The surface temperature of the far-infrared irradiation heater was controlled to a constant value, the temperature of the rice at the outlet of the bell converter 4 was set at about 35°C, and the temperature of the rice after tempering was kept at about 10°C, which was the outside air temperature, by rotating the blower 13. As a result, the rate of moisture reduction in paddy was 0.8% per hour.

When this is multiplied by (tempering time/irradiation time), that is, when converted into irradiation time, it becomes 2% per minute, which is a very high drying rate per irradiation time.

The resulting dry product had a shell cracking rate of less than 2%, and was satisfactory in terms of quality.

(Effects of the Invention) According to the present invention, by irradiating with far infrared rays, it is possible to reduce the temperature difference between the inside and outside of the rice grains, thereby making it possible to obtain dried rice grains without shell cracking and with good flavor in a short time.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of an apparatus used to carry out the method of the present invention. 1...Storage fi, 4.11...Belcon 5...Far-infrared irradiation heater l 5...Paddy

Claims (3)

[Claims] (1) Spread the rice in a thin layer, irradiate it with far infrared rays at a temperature and time that does not cause the rice to crack, then let it cool and temper, and repeat this far infrared ray irradiation and tempering. A distinctive method of drying paddy. (2) The method for drying rice according to claim 1, wherein the far-infrared ray irradiation time is 5 seconds to 1 minute per time. (3) The method for drying rice according to claim 1 or 2, wherein the temperature of the rice irradiated with far infrared rays is 30°C to 40°C.