Rice naturally has a brownish grain surface. To give it its beautiful white colour, whitening machines are used in the first step.
Via a feed screw, the rice is fed into the working chamber of the whitening machine where a conical stone set on a hollow shaft is surrounded by a conical screen basket. The outlet of the working chamber is completed by a plate the counter-pressure of which can be variably adjusted by springs. One special aspect worth mentioning is the gap adjustment between the whitening stone and the screen basket. By adjusting the height of the stone set, the distance and thus the intensity can be adjusted variably, even during operation.
The rice passes through this working chamber and is whitened by the stone set. The resulting bran is sucked off through the screen basket. To obtain the strong white colour and to whiten the rice simultaneously with a minimum percentage of broken rice, two or more whitening machines are used in succession.