Milling the rice can yield as many as 4 to 40 percent broken kernels depending on the quality of the incoming rice and the milling equipment. Most high quality rice is sold with less than 4 percent brokens and so brokens must be removed in the milling process. The rice is passed through rice grader. These can be cylinders with small pockets too small for whole grain to fit into, but just rightfor brokens, or disks within a trough that have similar indents.
Either way, the idea is for the brokens kernels to temporarily fit into the indent so that they will be picked out of the whole kernels and then thrown into a separate flow. The brokens can then be passed over screens or additional indent graders to be further separated into various sizes. (brewers, screening, and second heads).
The investigations have shown, that the efficiency h du of the rice destoner unit is in the range of 84 - 86%. Yet one has to take into account that the surface of the path and the wheels, the pressure of the tyre, the pressure between the wheels etc. can decrease the efficiency to a considerable extent. Driven by a donkey, the capacity of the huller is between 250 and 300 kg of paddy/h. With one passage it is possible to dehusk about 90-95% of the rice. After a second passage the rice is completely dehusked. Because the second passage increases the capacity up to 400 kg/h, dehulling with two passages translates to a total capacity of 150 to 200 kg paddy/h, the traditional method of rice-hulling produces 15 to 20 kg paddy/h-about 15 times less than the animal-powered rice-huller.