May 25, 2008

Rice Processing: Milling

Rice Processing: Milling
Harvested at 18 – 25% moisture, rice is mechanically dried to less than 15% moisture on the farm, at a commercial dryer, or at the mill before storage or processing. Rough cleaning (removal of sticks, stones, dust, and other foreign material) may precede drying, which is usually done in upright continuous flow dryers with a concurrent flow of heated air. After cooling, the dried rice is cleaned by various separation methods to give rough rice or “paddy”.

Some paddy is parboiled or converted by being soaked in water, then drained, steamed to gelatinize the starch, and dried again. This traditional process may increase the nutritive value by distributing soluble B vitamins from the bran into the endosperm, and it may stabilize against insects and lipolytic rancidity, but it does not decrease consumer cooking time.

Most paddy is hulled between rubber rolls turning in opposite directions, aspirated to remove hulls, and separated from the unhulled or rough rice in a paddy machine or gravity table to give brown rice. Most parboiled rice is prepared from brown rice by the steps already outlined for parboiling.

Finally comes the most important rice milling operation, removal of some or all of the bran layers by abrasion, or “pearling”, as it is called. After removal of the pearlings by aspiration, the milled or white rice is separated by size into heads (unbroken kernels), second heads (larger broken kernels), brewers’ rice (smallest broken kernels), and screenings. Although this grades have other even more important uses, head rice is used for puffing and second heads for rice flakes. If rice is desired as a component of a formulated flaked, shredded, or extruded cereal, rice flour made from grinding second heads or brewers’ rice is used.
Rice Processing: Milling

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