Introduction

Paddy in its raw form cannot be consumed by human beings. It needs to be suitably processed for obtaining rice. Rice milling is the process which helps in removal of hulls and barns from paddy grains to produce polished rice.
Rice forms the basic primary processed product obtained from paddy and this is further processed for obtaining various secondary and tertiary products. Grain enters the indent cylinder at the feed inlet situated at the high end of the sloping cylinder. The undersize grain is captured by the indents and is carried up as the cylinder revolves untill a point is reached where the grain is dislodged by gravity and is collected in a flared trough screw conveyor and discharged.
The full grain remains in the bottom of the cylinder and because of the inclination of the cylinder travels to a separate discharge outlet.

Milling is a crucial step in post-production of rice. The basic objective of a rice milling system is to remove the husk and the bran layers, and produce an edible, white rice kernel that is sufficiently milled and free of impurities.  Depending on the requirements of the customer, the rice should have a minimum of broken kernels.

Most rice varieties are composed of roughly 20% rice hull, 11% bran layers, and 69% starchy endosperm, also referred to as the total milled rice. Total milled rice contains whole grains or head rice, and brokens. The by-products in rice milling are rice hull, rice germ and bran layers, and fine brokens.

A rice milling system can be a simple one or two step process, or a multi stage process. In a one step milling process, husk and bran removal are done in one pass and milled or white rice is produced directly out of paddy. In a two step process, removing husk and removing bran are done separately, and brown rice is produced as an intermediate product. In multistage milling, rice will undergo a number of different processing steps.

PAVIZHAM RICE milling systems mill the paddy in stages, and hence are called multi-stage or multi-pass rice mills. The objective of commercial rice milling is to reduce mechanical stresses and heat buildup in the grain, thereby minimizing grain breakage and producing uniformly polished grain. Compared to village-level systems, the commercial milling system is a more sophisticated system configured to maximize the process of producing well-milled, whole grains.

The rice milling facility comes in various configurations, and the milling components vary in design and performance. “Configuration” refers to how the components are sequenced. The flow diagram below shows a modern commercial mill catering to the higher end market. It has three basic stages, the husking stage, the whitening-polishing stage, and the grading, blending, and packaging stage.

In PAVIZHAM rice mills, many adjustments (e.g. rubber roll clearance, separator bed inclination, feed rates) are automated for maximum efficiency and ease of operation. The whitener-polishers are provided with gauges that sense the current load on the motor drives which gives an indication of the operating pressure on the grain. This provides a more objective means of setting milling pressures on the grain.

                 
Milling section

Modern rice milling processes consist of:

Pre Cleaning : Removing all impurities and unfilled grains from paddy

De-stoning : Separating small stones from paddy

Parboiling (Optional) : Helps in improving the nutritional quality by gelatinization of starch inside the rice grain. Itimproves the milling recovery percent during deshelling and polishing / whitening operation 4. Husking :Removing husk from paddy
Husk Aspiration : Separating the husk from brown rice/ unhusked paddy

Paddy Separation : Separating the unhusked paddy from brown rice.

Whitening : Removing all or part of the bran layer and germ from brown rice

Polishing : Improving the appearance of milled rice by removing theremaining bran particles and by polishing the exterior of the milled kernel.

Length Grading : Separating small and large brokens from head rice

Blending : Mixing head rice with predetermined amount of brokens, as required by the customer

Weighing and bagging : Preparing the milled rice for transport to the Customer

1 -  paddy is dumped in the intake pit feeding the pre-cleaner
2 -  pre-cleaned paddy moves to the rubber roll husker:
3 -  mixture of brown rice and unhusked paddy moves to the separator
4 -  unhusked paddy is separated and returned to the rubber roll husker
5 – brown rice moves to the destoner
6 -  de-stoned, brown rice moves to the 1st stage (abrasive) whitener
7 -  partially milled rice moves to the 2nd stage (friction) whitener
8 – milled rice moves to the sifter
9a - (for simple rice mill) ungraded, milled rice moves to bagging station
9b – (for more sophisticated mill) milled rice moves to the polisher
10 - Polished rice, will move to length grader
11 - Head rice moves to head rice bin
12 – Brokens moves to brokens bin
13 – Pre-selected amount of head rice and brokens move to blending station
14 – Custom-made blend of head rice and brokens moves to bagging station
15 – Bagged Rice moves to the market
A – straw, chaff and empty grains are removed
B  - husk removed by the aspirator
C – small stones, mudd balls etc. removed by de-stoner
D -  Coarse (from 1st whitener) and fine (from 2nd whitener) bran removed from the rice grain during the whitening process
E - Small brokens/brewer’s rice removed by the sifter

Paddy Pre-Cleaner

Although harvested paddy grain may have gone through a cleaner before drying, wet paddy is difficult to clean thoroughly. Cleaning paddy prior to husking and whitening is crucial in attaining high milling recoveries.
 

A simple pre-cleaner used in rice mills usually contain an oscillating double screen bed with an aspirator. The first screen is a scalper that lets through the grain but retains straw. The second screen retains the grains but lets through broken grains and small stones or weed seeds. The air aspirator sucks out dust and the light empty grains.   Air dampers are provided and have to be adjusted to prevent the good grain from being sucked out.  The diagram shows a more sophisticated design that uses a rotary drum as scalper, and a screen for separating the fines. 

Rubber-Roll Husker

Husking or de-hulling is a process for removing the rice hull from the rough rice. The rubber roll husker is by far the most important technology used today for husking rough rice.
 

Rough rice is fed via a hopper and supplied to the two rubber rolls. One roller rotates clockwise, and the other counter clockwise at a faster speed. This provides a shearing action that strips off the husk while paddy drops between the rollers (see diagram). The rubber on the roles is flexible and does not crush the grain. Rice husk and broken rice are removed from the husked material at the winnowing section which is referred to as aspirator.  In the aspirator the material is divided into a mixture of brown rice, unhusked whole grains, and rice husk.  The husked material is taken out by suction of the aspirator fan. After passing through the rubber roll husker, the brown rice and unhusked paddy grain will move the next step: the paddy separator.

Paddy And Brown Rice Separator, And De-stoner

Paddy separation is as important as the rice husker and whitener. As no husker is 100% efficient, some paddy will be discharged together with the brown rice after husking. Separators are needed to prevent paddy grain from entering the whitening section of the mill, and to recover unhusked grains.  In larger rice mills, separators are independent from the husker. The separator separates husked rice into three categories, namely brown rice, rough rice, and a mixture of the two. The brown rice is collected from the outlet and will move on to de-stoning and whitening sections.  The rough rice will be returned to the rubber roll husker.  The mixture will be returned to the inlet of the separator

The de-stoner is an important component of the rice mill, particularly when rice is harvested mechanically, or when rough rice is dried on open pavements. The grain gathers a lot of stones and mudball during handling, which must be removed.  The de-stoner is a simple vibrating deck and air blower that suspends the grain from the stones. The stones are thrown off in one end and the brown rice in the other end.

Destoner

Whitening And Polishing Of Brown Rice
           

In compact rice mills whitening and polishing is a one step process. This generates a lot of heat in the kernel, as grain undergoes friction forces through the effects of scraping.  The result is heat build up in the grain, and grain breakage and low milling recovery.  To avoid breakage, the multi-pass whitening-polishing process was developed.  The objective of the multi-pass system is to minimize breakage by reducing heat buildup in and friction on the grain.

Sorting Rice

                              
Camera sencers                                     Sorting machine

In a rice sorting machine,  Rice enters the machine through the input hopper and is vibrated towards th anodized aluminum chute along a tray. The rice drops off the edge of the tray onto the chute and slides down. The chute has the effect of separating the grains so they arrive at the end in a continuous stream. At the end of the chute there is a detector head consisting of a number of cameras. An image is taken of each grain as it passes the head. The image is quickly processed and compared to a reference standard that is used to accept or reject the grain. A series of air jets controlled by high speed poppet valves are used to blow the defective grains or contaminants out of the stream.The machine is very effective at rapidly sorting rice .The process can be used to sort lower quality and dirtier rice to remove husk and contaminating particles. Using the machines for increasingly dirty product has meant that greater wear has occurred as this type of rice has a large element of husk present and other contaminants which are highly abrasive.

Packing Section

Separation of highly sorted rice from harvested paddy is followed by packing the finished product inorder to reach the customers in good condition.

Customers health is given main priority in Pavizham. For attaning it, the entire process of packing is carried out in hygeinic environment using high end packing technology. The workers are also gven special traning for maintaining the quality of product.

Keeping in mind all these things, Pavizham Healthier Diet Pvt Ltd. has grown up in the market as rice & rice products dealer in order to serve the quality end rice products to their customers.