Pre-Cleaning: When paddy comes into the mill it contains foreign material such as straw, weed seeds, soil and other inert material. If this is not removed prior to hulling the efficiency of the huller and the milling recovery are reduced. Most pre-cleaners separate three groups of materials.
The first separation is done by scalping or removing the objects that are larger than the grain. Either a flat oscillating screen or a rotary drum screen that allows the grain to pass through but retains straw can do this. The second separation retains the grains but allows broken grains, small stones and weed seeds to pass through. An air aspirator may also be incorporated to remove the dust and the light empty grains The capacity of the paddy pre-cleaner is usually based on the capacity of the rice mill. A pre-cleaner for a 3-ton/hr rice mill would normally have a 5 ton/hr cleaning capacity.
De-Husking: The husk layer is removed from the paddy by friction and the process is called either de-husking or de-hulling. De-husking was traditionally done using mortar and pestles but, in modern rice mills, it is done by passing the paddy grains between two abrasive surfaces that are moving at different speeds. After separating the husk and paddy, the husk is removed by suction (aspirated) and then transported to a storage dump outside the milling plant. The percentage of paddy that is de-hulled to produce brown rice during this process is called the hulling efficiency An efficient husker will remove 90% of the husk in a single pass. After the husk has been removed the brown rice goes to a paddy separator. The kernels that were not de-husked in the first pass will be separated and then returned to the de-husker.
Final, The process of brown rice is completed. Any manufacturer may use cylindrical grader or tray separator to segregate broken brown rice and full grain brown rice.