This invention relates to a process and apparatus for continuous pressure steaming of rice and other grains.
Background:
Basmati rice is a preferred rice variety both in India as well as in many countries worldwide. It commands a premium price. Its superiority stems from its slender shape, pure white color, and a very pleasant aroma, that's often described as heavenly.
However, when Basmati is prepared for large number of servings, as in a restaurant, the prepared rice gets soft and mushy in a short period of time, when held warm for a period of time. One solution would be to use the soaking and steaming process as used in "Sella" rice, which is sold mostly in Saudi Arabia. This process is otherwise called parboiling. During parboiling, rice paddy is briefly steamed at atmospheric pressure, soaked in warm water for several hours, and then soaked paddy is steamed again for a brief period of time at atmospheric pressure. Later the steamed paddy is dried, shelled, and milled. Parboiling changes the grain's eating quality as well as physical properties, i.e. makes it creamy yellow in color, makes the grains firm and plump, and all pleasant aroma is lost and replaced with earthy aroma.
Recently, to counter the effects of parboiling CFTRI has developed and made available to all processors a process wherein, paddy is steamed at atmospheric pressure for a period of time and then, dried, shelled and milled. The rice thus obtained is more similar to the unprocessed rice, but is not always uniform in color. Steaming at atmospheric pressure does not permit uniform treatment, as the paddy close to the steam injection point is more processed compared to paddy located further away from the injection point. This leads to non-uniform color in the milled rice, and also the cooked product has varied degree of firm and mushy grains. This variability makes the product unacceptable
The object of the present invention is to obviate the above drawbacks by pressure steaming of variety of rice and grain at uniform steam pressure and retention time to get rice of uniform appearance and cooking quality.
To achieve the said objective, this invention provides a process for continuous steaming of paddy rice and other grains at uniform steam pressure and retention time comprising:
feeding cleaned paddy or grain variety to a feed hopper placed on the continuous
steaming pressure vessel of plug flow type for processing said cleaned paddy or
grain variety,
providing said pressure vessel with a steam control valve, a feed airlock and a
discharge airlock and mounting said vessel on a set of load cells to control
retention time for said clean paddy or grain variety in a vessel during steaming
process,
connecting programmable logic controller (PLC) to the steam control valve, the
load cells, the feed airlock and the discharge airlock to select the steam pressure,
the retention time, feed and discharge rate for the preparation of variety of rice or
grain at uniform steam pressure and retention time,
passing steam through said steam control valve into the vessel and maintain the
required steam pressure in the vessel through said PLC,
releasing required quantity of variety of cleaned paddy or grain from the feed
hopper through the feed airlock into the vessel on said load cells, till the desired
weight of said paddy or grain is reached, running the discharge airlock to
discharge the steamed variety of paddy rice or grains after controlled retention
time, with constant velocity of flow throughout the vessel and controlled steam
pressure,
drying the variety of steamed paddy or grain, shelling, separating and milling the
variety of paddy or grain to get rice or grain of uniform appearance and cooking
quality.
The steaming condition for Basmati type varieties for production of steamed product is as follows: Table
(Table Removed)
The steaming condition for Permal, a non-Basmati long grain variety is 70 kPa for 10 minutes.
The steaming condition for wheat to make bulgar is 56 kPa for 10 minutes.
The steaming condition can be varied to obtain product with desired degree of gelatinization.
The invention further includes an apparatus for carrying out the process for continuous pressure steaming of variety of paddy rice and grains at uniform steam pressure and retention time comprising:
pressure rated vertical vessel with plug flow characteristic using 70-80° cone at
the discharge end of said vessel,
top and bottom of said vertical vessel having a feed inlet airlock and discharge
outlet airlock respectively,
said feed inlet airlock is connected to the feed hopper to feed the paddy rice or
grains to said vessel,
said vertical vessel is provided with a steam inlet control valve and is mounted on
a set of load cells to control steam pressure and retention time of said paddy and
grain during the steaming process,
a programmable logic controller (PLC) connected to the feed inlet airlock,
discharge outlet airlock, steam control valve and the load cells to set the
parameters of the process namely control retention time for said paddy or grains,
steam pressure in said vertical vessel,
said discharge outlet airlock is connected to a conveyor, a dryer, a sheller, a separator and a miller for drying, shelling, separating and milling the paddy rice or grain of uniform appearance and cooking variety.
The said pressure rated vertical vessel is provided with flow equalizer cone between the bottom of the vertical vessel and said discharge airlock.
The said pressure rated vessel is insulated and has controlled rice paddy level for preventing heat loss and maintaining retention time.
The said vertical vessel is provided with pressure relief valve and the vacuum breaker on its top for safety.
A programmable logic controller is provided for steam pressure and retention time control through steam control valve and the inlet airlock.
The present invention also relates to variety of rice and other grains of uniform appearance and cooking quality whenever prepared by the above process and the apparatus.
Brief Description of the Drawings
The invention will now be described with reference to the accompanying drawings.
Figure 1 shows a process for continuous steaming of paddy rice or other grains at uniform steam pressure and retention time.
Figure 2 shows an apparatus for carrying out the process for continuous pressure steaming of paddy rice and other grains.
Detailed Description:
Referring to figures 1 and 2 paddy rice of Basmati variety or any rice or any grain variety to be processed is first cleaned to remove dust, empty hulls and other farm impurities like straw, stalks and the like. This cleaned paddy or grain variety is stored in clean paddy bins (1) and then as required is placed in a feed hopper (2) above the feed inlet airlock (3) of the vertical pressure steaming vessel (4) having discharge outlet airlock (5) at the bottom.
The said vessel (4) is mounted on a set of load cells (10) that are used to control retention time in the steaming process. Also, the vessel (4) is connected to a steam supply line (9) via control valve (8) that is used to maintain a desired steam pressure in the vessel (4). The vessel (4) is designed to assure plug flow, which is constant velocity of flow throughout the vessel. A cone (11) is placed above the discharge airlock (5) to allow plug flow out of the steaming vessel (4).
Based on the quality of the desired product and also on the variety of Basmati rice, retention time and steam pressure set points are selected. Programmable Logic Controller (PLC) (8a) is used to control the process' set parameters. Required set points are set on the PLC controller to start the process. Steam control valve (9) will allow steam into the vessel (4) and maintain the required steam pressure as set on the PLC controller (8a) set point. The feed inlet airlock (3) will speed up to deliver the required weight of clean paddy based on retention time and throughput rate of the process. This desired weight when reached will turn on the discharge airlock (5) and run it at a fixed speed to take away steamed rice at the desired through put rate of the process. Controlled residence time, constant velocity of flow throughout the vessel, and controlled pressure assures each and every grain to be exposed to the same steam pressure and retention time. After steaming, the paddy is dried, shelled, separated and milled using conventional equipment.
Figure 2 shows the continuous pressure steaming vessel consisting of a feed inlet airlock (3), said vessel (4) is having pressure relief valve (6) and a vacuum breaker (7) for safety. The said vessel (4) is provided with a steam inlet control valve (8) and is
mounted on a set of load cells (10) to control steaming pressure and retention time of said paddy rice or grains during the steaming process.
A Programmable Logic Controller (PLC) (8a) is connected to feed inlet airlock (3), discharge outlet lock (5), steam control valve (8) and load cells (10) to set the parameters of the process, namely, control retention time for said paddy or grains, steam pressure in said vertical vessel (4). The said discharge outlet airlock (5) is connected to a conveyor (C), a dryer (D), sheller (SH), separator (S) and a miller (M) for drying, shelling, separating and milling the paddy rice or grain of uniform appearance and cooking quality and thereafter storing in the bins (B), as shown in figure 1.
The invention will now be described with reference to the following examples:
Example I:
For Traditional Basmati variety paddy, cleaned paddy would be supplied via the feed hopper (2) to the pressure steaming vessel (4). Optimum pressure to obtain the desired product with a white color and fluffy appearance of cooked rice; the steaming condition would be 77 kPa for 3 minutes. Based on the flow rate desired multiplied by retention time of 3 minutes, the amount of rice to be held in the steaming vessel (4) is determined and that is set as the set point in the PLC controller (8a) for retention time. Vessel (4) is preheated and set at the desired pressure of 77 kPa using the PLC (8a) for steam pressure control. Top airlock (3) is operated by PLC to feed steaming vessel (4). When the desired weight is reached, the bottom airlock (5) is operated at fixed speed to take away desired flow rate. Now the feed airlock (3) will operate at speed determined by the PLC controller (8a) to maintain set point for retention time. Thus, every grain is steamed at a uniform pressure for said retention time to provide surface gelatinization of each grain. Severity of process condition will permit required degree of gelatinization. The table below gives steaming conditions for other Basmati like varieties.
Table 1:
Steaming Conditions for Basmati Type Varieties for Production of Steamed Rice Product

(Table Removed)
Example II:
The same vessel may also be used to make ordinary parboiled rice from any long grain variety, i.e. Pre-cleaned paddy of Permal variety is soaked in 65 degrees C water till paddy moisture is 35% wet weight basis. Paddy is drained and then would be supplied via the feed hopper (2) to the steamer vessel (4). Optimum pressure to obtain the desired product with a white color and fluffy appearance of cooked rice; the steaming condition would be 70 kPa 10 minutes. Based on the flow rate desired multiplied by retention time of 10 minutes, the amount of rice to be held in the steamer vessel (4) is determined and that is set as the set point in the PLC controller (8a) for retention time. Vessel (4) is preheated and set at the desired pressure of 70 kPa using the PLC (8a) for steam pressure controller. Top airlock (3a) is started to feed the steamer vessel (4). When the desired weight is reached, the bottom airlock (5) is started at fixed speed to take away desired flow rate. Now the feed airlock (3) will operate at speed determined by the PLC controller (8a) to maintain set point for retention time. Thus, every grain is steamed at a uniform pressure for said retention time to provide full gelatinization of each grain. Severity of process condition will permit required degree of gelatinization.
Example III:
Also, the said pressure vessel maybe used to gelatinize other grain variety, i.e. wheat to produce bulgar. Wheat grain of any variety is cleaned, soaked to 35% moisture content (wet weight basis) and then would be supplied to the feed hopper (2) to the steamer
vessel (4). Optimum pressure to obtain the desired product quality; the steaming condition would be 56 kPa for 10 minutes. Based on the flow rate desired multiplied by retention time of 10 minutes, the amount of rice to be held in the steamer vessel (4) is determined and that is set as the set point in the PLC controller (8a) for retention time. Vessel (4) is preheated and set at the desired pressure of 56 kPa using the PLC (8a) for steam pressure controller. Top airlock (3a) is started to feed the steamer vessel (4). When the desired weight is reached, the bottom airlock (5) is started at fixed speed to take away desired flow rate. Now the feed airlock (3) will operate at speed determined by the PLC controller (8a) to maintain set point for retention time. Thus, every grain is steamed at a uniform pressure for said retention time to provide full gelatinization of each grain.

We claim:
1. A process for continuous steaming of paddy rice and other grains at uniform
steam pressure and retention time comprising:
feeding cleaned paddy or grain variety to a feed hopper placed on the
continuous steaming pressure vessel of plug flow type for processing said
cleaned paddy or grain variety,
providing said pressure vessel with a steam control valve, a feed airlock
and a discharge airlock and mounting said vessel on a set of load cells to
control retention time for said clean paddy or grain variety in a vessel
during steaming process,
connecting programmable logic controller (PLC) to the steam control
valve, the load cells, the feed airlock and the discharge airlock to select the
steam pressure, the retention time, feed and discharge rate for the
preparation of variety of rice or grain at uniform steam pressure and
retention time,
passing steam through said steam control valve into the vessel and
maintain the required steam pressure in the vessel through said PLC,
releasing required quantity of variety of cleaned paddy or grain from the
feed hopper through the feed airlock into the vessel on said load cells, till
the desired weight of said paddy or grain is reached, running the discharge
airlock to discharge the steamed variety of paddy rice or grains after
controlled retention time, with constant velocity of flow throughout the
vessel and controlled steam pressure,
drying the variety of steamed paddy or grain, shelling, separating and
milling the variety of paddy or grain to get rice or grain of uniform
appearance and cooking quality.
2. A process as claimed in claim 1 wherein the steaming condition for Basmati type
varieties for production of steamed product is as follows: Table
(Table Removed)
3. A process as claimed in claim 1 wherein the steaming condition for Permal, a
non-Basmati long grain rice is 70 kPa for 10 minutes.
4. A process as claimed in claim 1 wherein the steaming condition for wheat to
make bulgar is 56 kPa for 10 minutes.
5. A process as claimed in claim 1 wherein the steaming condition can be varied to
obtain product with desired degree of gelatinization.
6. An apparatus for carrying out the process for continuous pressure steaming of
variety of paddy rice and grains at uniform steam pressure and retention time
comprising:
pressure rated vertical vessel with plug flow characteristic using 70-80°
cone at the discharge end of said vessel,
top and bottom of said vertical vessel having a feed inlet airlock and
discharge outlet airlock respectively,
said feed inlet airlock is connected to the feed hopper to feed the paddy
rice or grains to said vessel,
said vertical vessel is provided with a steam inlet control valve and is
mounted on a set of load cells to control steam pressure and retention time
of said paddy and grain during the steaming process,
a programmable logic controller (PLC) connected to the feed inlet airlock,
discharge outlet airlock, steam control valve and the load cells to set the
parameters of the process namely control retention time for said paddy or grains, steam pressure in said vertical vessel,
said discharge outlet airlock is connected to a conveyor, a dryer, a sheller, a separator and a miller for drying, shelling, separating and milling the paddy rice or grain of uniform appearance and cooking variety.
7. An apparatus as claimed in claim 5 wherein said pressure rated vertical vessel is
provided with flow equalizer cone between the bottom of the vertical vessel and
said discharge airlock.
8. An apparatus as claimed in claim 5 wherein said pressure rated vessel is insulated
and has controlled rice paddy level for preventing heat loss and maintaining
retention time.
9. An apparatus as claimed in claim 5 wherein said vertical vessel is provided with
pressure relief valve and the vacuum breaker on its top for safety.
10. An apparatus as claimed in claim 5 wherein a programmable logic controller is
provided for steam pressure and retention time control through steam control
valve and the inlet airlock.
11. A process for continuous steaming of paddy rice and other grains at uniform
steam pressure and retention time substantially as herein described with reference
to and as illustrated in the accompanying drawings
12. An apparatus for carrying out the process for continuous pressure steaming of
variety of paddy rice and grains at uniform steam pressure and retention time
substantially as herein described with reference to and as illustrated in the
accompanying drawings.
13, Variety of rice and other grains of uniform appearance and cooking quality whenever prepared by the process and the apparatus as claimed in the preceding claims.