Rice naturally has a brownish grain surface. To give it its typical intense white colour, the SCHULE whitening machine is used in a second process step after shelling.
Via a feed screw, the rice is fed into the working chamber of the whitening machine where a set of conical stones with air channels in between is arranged on a hollow shaft which 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. Depending on the intensity, the surface is whitened more or less intensively and the adhering impurities are removed. The produced whitening bran is sucked off through the screen basket by means of a separate, laterally mounted aspiration connection.
Air cools the product during the whitening process and at the same time facilitates the discharge of adhering whitening bran. To obtain the intense white colour and to whiten the rice simultaneously with a minimum percentage of broken rice, two or more whitening machines are used in succession.
Advantages of the conical whitening machine:
• Gentle treatment
• Variable gap adjustment
• Uniform load
In order to obtain an even higher quality of the final product, the whitened product is fed into the subsequent process step, i.e. polishing.