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Beyond the Ri’ichi: Part 4:
Processing long-grain rice - Milling
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by Hiromi Saita, Senior Staff, International Management Office, Satake Corporation, Japan
he most important consideration in milling long-grain rice is proper control of the polishing pressure. If the pressure is too low, then rice milling will not progress correctly. If the pressure is too high, it will break the rice grain. Milling long-grain using Japanese equipment for short-grain generates a large amount of broken rice. This is mainly due to the inner pressure of the frictional milling machine, which is specifically designed to be high for short-grain rice milling. Long-grain rice cannot resist such high pressure and, thus, cracks. Moreover, high value varieties such as Basmati and Jasmine rice, mainly for exports, (and whose production yield impacts directly on profits), are even more likely to present a high broken rice rate, even compared to other long-grain rice varieties. For that reason, careful attention must be paid to the selection of equipment and the operation of these varieties of rice. In addition, the temperature rise of the rice grain during the milling process causes the loss of its natural aroma, hence a suppression of this temperature rise is fundamental. Since it is rare to find overseas rice processing plants handling wide varieties of rice in small lots like those in Japan, it is more critical to maintain stable performance over time once a machine is installed. Having stable machine performance without using complicated mechanisms such as automatic weight control, like the kinds used in Japan, is desirable. Some Parboil rice production plants may mix a small amount of calcium carbonate with the raw materials. Parboil rice bran is usually more viscous than brown rice’s bran and tends to accumulate inside the machinery and, thus, gives rise to more frequent cleaning. However, adding calcium carbonate can remove the bran deposit from the outset, thereby improving the cleaning frequency of the rice milling machine. However, the abrasion action of calcium carbonate also causes wear of the screen of the rice milling machine and the machine 68 | March 2020 - Milling and Grain
itself. For this reason, white pig iron cast iron with improved wear resistance is used in the casting part, and the plate thickness of the part where the consumption is severe is increased in advance. Depending on its variety, the shape (length, width, thickness), the bran thickness and the fragility of the rice, endosperm can be different. Although the milling characteristics of the rice can be determined from its country of origin and its variety to a certain level, ripeness, drying and husking processes do cause a wide range of different characteristics. Satake combines abrasive, friction and wet milling types to provide high-quality, high yield rice milling which is unique to each milling facility. Specifically, the pressure needed for milling is dispersed as much as possible by adding the pressure gradually for four-to-five passes to minimise the grain temperature rise and broken rice. To seek high yield and quality, some facilities are using seven-to-eight milling machines to mill the rice. The orientation of rice grain in the milling machine is also very important. If the pressure is applied to the weak belly part, the rice grain will break, and if the pressure is applied only to the tip that holds the germ, only that part will break and become broken at the nose. Satake has established a rice milling technique for sake milling machines that maintains the rice kernel shape while maintaining peripheral speed and pressures. This technique is used to control the orientation of the rice inside the machine. The combination of rolls, screen and pulleys creates the optimum rice attitude and working pressure, while also controlling the brittle parts of the rice grain so that no excessive force is applied to it. Satake’s milling machinery for the overseas use mainly consist of abrasion VTA, friction VBF, and wet milling KB. Nowadays, the VTA and VBF are the mainstream models in Japan but these models were originally created from the needs of overseas customers in the early 1990s. By making the milling chamber vertical, (previously, it had been horizontal) rice can be filled to the full capacity in the milling chamber and can be polished uniformly and efficiently. Since then, due to the rice shortage