Context 

In a letter to Agromisa, Sr. Kips of Medicins sans Frontières in Kasenga, Zaire, requested for documentation and prices of rice-hullers. Agromisa provided a description of the two main methods of rice-hulling (disc-hullers and rubber roll hullers) and a list of providers, based on the 1992 publication of ITDG/CTA on Small-scale food processing (see linked bibliographical reference)

Finally she ordered one from Belgium, which appeared to be produced in the Netherlands, by Votex BV, Andelst (see attached files for equipment and address data)

Description/Implementation

 A disc huller consists of two horizontal, parallel discs, coated with an abrasive. The upper disc is static, the lower disc moves. The distance between the two discs is smaller than the grain length. If the discs are too wide apart, insufficient rice is hulled. If the distance is too small, many grains breach. This type of huller works well with rice-grains of equal size, without beard.

Advantages of this type: Simple design, simple operation. Low cost of operation. The abrasive layer on the discs is the most sensitive to wear, but it works well for a reasonable time. The layer can be replaced easily, and c an be made locally.

Disadvantages: Much damage of rice-grains is caused if different grain lengths are entered into the machine at the same time: Much germ is removed, long grains are shortened and stumped, the brown outer layer of rice is removed and a chaffed product has to be sieved to remove the germ before the grains can be separated from the husk.

Rubber roll hullers press the rice grains between two rubber rolls turning in the same direction at different speeds. In this process the hull is stripped off the grain. The distance between the rolls is smaller than the width of the grain. The process is efficient, but the rubber rolls need to be replaced regularly (after app. 800 tons of rice, according to Grist), since the rubber wears considerably. It is often difficult to get replacement rolls in time.

Advantages of the rubber roll huller:

Less breakage of grains. The kernel (germ) is not removed. The silver coat remains intact, which gives a higher yield of useful rice-bran upon polishing. No need for sieving husk and bran.

Disadvantages

Higher cost of operation of the machine due to the need to replace rolls.

Storage of rubber rolls for a longer time is not advisable, since it shortens the time of operation. A constant supply of rolls is therefore required.