A rice huller or rice husker is an agricultural machine used to automate the process of removing the chaff (the outer husks) of grains of rice. Throughout history, there have been numerous techniques to hull rice. Traditionally, it would be pounded using some form of mortar and pestle. An early simple machine to do this is a rice pounder. Later even more efficient machinery was developed to hull and polish rice.^[1] These machines are most widely developed and used throughout Asia, the most popular modern type in use today is the Engelberg huller designed by German Brazilian engineer Evaristo Conrado Engelberg in Brazil and first patented in 1885.^[2]

The Engelberg huller uses steel rollers to remove the husk. Other types of huller include the disk or cono huller which uses an abrasive rotating disk to first remove the husk before passing the grain to conical rollers which polish it to make white rice; this is done repeatedly since other sides of circular side of rice are not husked. Rubber rollers may be used to reduce the amount of breakage of the grains, so increasing the yield of the best quality head rice, but the rubber rollers tend to require frequent replacement, which can be a significant drawback.^[2]

The hulling operation starts with pre-processing, in which the paddy is cleaned to eliminate contaminants such as straw, weed seeds, soils, and other inert debris. This is typically done using aspiration and sieving systems to facilitate the efficient functioning of the hulling machine.^[3] Proper cleaning not only protects the equipment from damage but also enhances overall performance, with pre-cleaners generally built to handle volumes about 1.5 times the milling capacity. Once cleaned, the paddy is introduced into the huller at rates commonly ranging from 500 to 1000 kg per hour, depending on the machine's size and design.^[4]

During the main hulling phase, the cleaned grains move through the hulling unit, where friction generated by abrasive surfaces or rollers operating at different speeds strips the husk from the kernel, resulting in brown rice.^[3] Since the husk makes up roughly 20% of the paddy's mass, it is subsequently removed using airflow aspiration or vibrating screens, which separate the lighter husk from the heavier brown rice and any remaining unhusked grains. Well-optimized hullers can achieve dehulling efficiency of up to 90% in a single pass, reducing the need for repeated processing.^[3]

The final stage involves post-hulling separation, where the output is sorted to distinguish between brown rice and any remaining unhusked grains and byproducts.^[3] This is usually carried out using aspiration systems or screening methods, ensuring proper classification and quality control in semi-continuous milling operations.

• Rice hulls
• Rice polisher
• Rice pounder, an earlier simple tool to dehull rice
• Threshing machine, a general machine to remove the grains from the straw or panicles
• Winnowing barn, a previous method of hulling in commercial rice growing