Parboiled rice


Parboiled rice is rice that has been
partially boiled in the husk. The three basic steps of parboiling are soaking,
steaming and drying. These steps also make rice easier to process by hand,
boost its nutritional profile and change its texture. About 50% of the world’s
paddy production is parboiled. The treatment is practiced in many parts of
the world such as India, Bangladesh, Pakistan, Myanmar, Malaysia, Nepal, Sri
Lanka, Guinea, South Africa, Italy, Spain, Nigeria, Thailand, Switzerland,
USA and France. Rice is easier to polish by hand after
parboiling but mechanical processing is harder since the bran becomes somewhat
oily and tends to clog machinery. Most parboiled rice is milled in the same way
as white rice. Parboiling drives nutrients, especially
thiamin, from the bran to the endosperm, hence parboiled white rice is 80%
nutritionally similar to brown rice. Because of this, parboiling was adopted
by North American rice growers in the early 20th century.
Process and chemistry The starches in parboiled rice become
gelatinized, then retrograded after cooling. Through gelatinization,
alpha-amylose molecules leach out of the starch granule network and diffuse into
the surrounding aqueous medium outside the granules which, when fully hydrated
are at maximum viscosity. The parboiled rice kernels should be translucent when
wholly gelatinized. Cooling brings retrogradation whereby amylase molecules
re-associate with each other and form a tightly packed structure. This increases
the formation of type 3-resistant starch which can act as a prebiotic and benefit
gut health in humans. However, this also makes the kernels harder and glassier.
Parboiled rice takes less time to cook and is firmer and less sticky. In North
America parboiled rice is either partially or fully precooked before
sale. Minerals such as zinc or iron are added, increasing their potential
bioavailability in the diet. Huzenlaub Process
In older methods, clean paddy rice was soaked in cold water for 36–38 hours to
give it a moisture content of 30-35%, after which the rice was put in
parboiling equipment with fresh cold water and boiled until it began to
split. The rice was then dried on woven mats, cooled and milled.
In the 1910s German-British scientist Erich Gustav Huzenlaub and the British
scientist and chemist Francis Heron Rogers invented a form of parboiling
which held more of the nutrients in rice, now known as the Huzenlaub
Process. The whole grain is vacuum dried, then steamed, followed by another
vacuum drying and husking. This also makes the rice more resistant to weevils
and lessens cooking time. In even later methods the rice is soaked
in hot water, then steamed for boiling which only takes 3 hours rather than the
20 hours of traditional methods. These methods also yield a yellowish color in
the rice, which undergoes less breakage when milled.
Graphical depiction of nutrition transfer
See also Rice congee
References

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