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Rice Polishing 150 years of innovation

“Nowadays, more and more rice mills are installing rice polishers that subject rice to multiple polishing passes. The degree of polishing has reached an all-time high” - Sujit Pande, Rice expert, Buhler

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ice is a vital staple food, feeding half of the world’s people and, according to the Food and Agricultural Organisation, providing as much as 20 percent of the global population’s dietary energy supply. In 2015, global rice farming produced 743 million tonnes of paddy rice – which yielded 493 million tonnes of white rice. Of this, an estimated 300 million tonnes of rice is polished. Originally, rice was consumed as unrefined, whole grain brown rice. The evolution of polished rice has changed our relationship with this staple food and with it, consumer tastes and demands. Today there are more than 40 000 different varieties of rice, each with their own characteristics, and each forming an integral part of the culinary traditions of many different regions and cultures. For instance, sushi and biryani from Asia, paella and risotto from Europe, as well as rice pudding - a British classic.

In demand

Until the late 20th century, rice mills around the world, including top-quality millers, did not integrate polishing into the production process. However, owing to the steadily increasing demand for whiter, silkier rice, the polishing process is now considered to be a crucial stage in the milling process. Although it is widely accepted that brown rice has a much higher nutritional value than white rice, many consumers prefer the taste of the polished white alternative. Furthermore, it easier to digest, needs no pre-soaking, cooks quicker and uses less water. It should be noted that the cooking process might cause the rice to burst, making it look coarser, which consumers can find offputting. However, this can be reduced, if the degree of polishing is adapted to suit the particular variety of rice. Polished rice has benefits for food producers and retailers too. It improves the appearance of the grain, making it more visually appealing at the point of sale, meaning it can command a higher price. It also removes traces of bran left after the whitening process. This is particularly important, as glycerides in the bran 58 | March 2016 - Milling and Grain

turn rancid when exposed to oxygen. If they are not removed, they reduce the shelf life and eventually result in a product that is unfit for consumption. However, the demand for high-gloss, transparent-looking rice in some parts of the world has been so high that unsafe, unapproved methods have been used to give the desired result. For instance, glazing the rice with non-food-safe additives, such as oil or talcum powder. Fortunately, an increasing number of rice mills are turning to innovative rice polishing technology to deliver new standards, improve quality, enhance food safety and deliver the degree of whiteness and silkiness that consumers demand.

Humble beginnings

Prior to the advent of modern polishers, several simpler methods were used including pounding the rice using a pestle and mortar, rubbing it on the floor, beating gently with clubs in jute bags and treading by humans and animals. These makeshift means, often carried out in poor hygiene conditions, not only required significant time and energy, but usually resulted in a poorly-finished and significantly damaged rice, with high levels of wastage. The first commercial rice polisher is widely believed to have been patented by the British engineer Sampson Moore. The inventor, a prominent engineer during the British Industrial Revolution, was credited in the London Gazette for his invention on June 21st 1861, for “improvements in the machinery or apparatus for dressing and polishing rice”. Since those early days, a range of machines have improved the efficiency and quality of milled, polished rice.

Rice polisher development

Unpolished rice naturally has a coarse surface, with ridges that protect individual grooves, where the bran sits. Prior to polishing, the rice must go through a whitening process, designed to level out undulations naturally found in the caryopses of all rice varieties and this helps to remove the majority of the bran. However, the abrasive elements used cannot be made fine enough to remove all of the bran without damaging the grain, which is why polishing is required. This gentler process, which removes dust, flour and bran residues, uses a pressing and rubbing technique to create friction. As the grains rub against each other, their surfaces are smoothed, removing the remainder of the bran, allowing more light to be reflected, which in turn makes the rice appear whiter and glossier. The first generation of polishers were adapted from whitening machines. They featured a similar vertical cone design but had two basic differences. The first was that the cone was made of a simplified steel wire construction and covered with wood, on to

Mar 2016 - Milling and Grain magazine  
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