Development And Performance Evaluation Of Rice Destoning Machine

2.3    Rice Processing
Rice processing involves several steps: removal of the husks, milling the shelled rice to remove the bran layer, and an additional whitening step to meet market expectations for appearance of the rice kernels. This process generated several streams of material which include the husks, the bran and the milled rice kernel (Schramm 2006). Nigeria has the potential to be self-sufficient in rice production, both for food and industrial raw material needs and for export purpose. However, a number of constraints have been identified as limiting factors to rice production. These include problems with research, pest and disease management. Addressing at least most of these problems is good first step towards attaining the target of rice self-sufficiency (WARDA 2004).
                 There are two methods of processing rice which are: The Traditional method of processing rice and the Modern method of processing rice.
2.4    The Traditional Method of Processing Rice
The traditional methods of processing rice paddy involve soaking of the paddy in water for 2 to 3 days to soften the kernel, followed by steaming of the soaked paddy for 5–10 minutes and dried in the sun as shown in plate 2.2 below, followed by pounding the dried paddy in a mortar and pestle device to remove the husk or use of simple machines for dehulling or milling; then the grain is cleaned using a winnowing basket (B. Srilakshmi, 2003). Though the traditionalmethod of processing rice is simple, but tedious, it has very low outturn and results in breakages of rice kernels and incomplete removal of husks. More so, it has a short storage life as the fat in the bran develops rancidity (B. Srilakshmi, 2003).
2.5    The Modern Methods of Processing Rice
Propoor Opportunities in Commodity and Service Markets Project (Propcom, 2012) carried out survey on modern rice processing and discovered that there has been improvement in rice processing in Nigeria compared to the 1990s. In modern methods, the rough rice or paddy is first cleaned to remove contaminants, and the husks are then removed by the so called shellers; these are most commonly horizontally spaced rotating abrasive stones, but increasing use is being made of rubber roll or rubber belt made shellers. The rice and hulls are separated by aspiration and any paddy remaining with the rice is removed in a paddy separator. It is discovered that the main problem of Nigerian rice is the presence of stone in the rice grains. The reported survey shows that there has been locally produced destoner made in Kano, Nigeria, as shown in plate 2.2. The machine costs N65,000 and was fabricated using angle iron and sheet metals.
             Another improvement in rice processing in Nigeria reported by Propcon is the drying process. The traditional sun drying has been replaced by mechanical dryer or improved sun drying method.This type of dryer is found scattered all over the country. It can process about 3000 kg and remove 50%moisture of rice in 6hrs.
      Apart from this mechanical dryer which uses diesel or electricity, other dryers have been developed such as solar dryer for drying rice paddy. An example of this is as shown in plate 2.3 developed in National Centre Solar Energy Research, Sokoto, Nigeria. The development of this is a result of incessant power outage all over the country. This type of solar dryer is equipped with fan to enhance hot air distribution over the rice paddy.
              Because local rice is of low quality, the rice merchants use this opportunity to expand on rice importation. The solution lies in the provision of incentives, machineries, and government policies to confront these challenges faced by rice processors.
2.6     Methods of De-stoning Rice
             There are two methods of de-stoning which are: Local or Traditional method of de-stoning and the Modern method of de-stoning.
2.7The Local or Traditional Method of De-stoning Rice
The local method of de-stoning involve: handpicking, which is the sorting and separation of rice from stones. Another method of the local method is done by winnowing of the rice manually and manual sieving of rice combine with stones.