Rice, Oryza sativa, is the most recognized staple food for more than half of the world population. It is widely grown in areas like China, Burma, India, Indonesia, Thailand, Nigeria and other south and Eastern Asian countries. There are two varieties of rice namely;
- Oryza sativa, this is the Asian type that has been widely cultivated.
- Oryza longistaminata , this exists in the wild form and mostly cultivated in the flooded plains.
The major problem facing the commercialization of rice is its quality. Most of the rice locally produced are inferior and has low value in the international market.
Good and high quality milled rice consists of unbroken, clean, stone free, no colour spot, less number of impurities and with no bad odour.
Based on these qualities, It is important that a good milling measure is adopted. Rice with the above qualities can be produced following the below steps;
Rice is harvested when the grains is dry and hard. This is at 30-40 days after flowering; the best indication is when about 80% of the head have turned straw colour. The panicle is cut about 15cm above the ground with either a sickle or combine harvester.
Harvesting is normally done from August- September for upland rice and October – November for swamp rice. This should be carried out at the appropriate time to reduce breakage of grains.
This is carried out soon after harvesting by beating the rice against the drums, floor or stick over dry mat or tarpaulin spread on the floor. This operation removes the rice paddy from the rice plant.
The paddy so removed by the process of threshing is dried to moisture content 13-14%. They are sun dried 2-3 days to reduce breakage during milling. Mechanized dryers can be used where available.
This is done by dropping dried paddy from a low height. It blows off dirt, empty grains, shaft and other foreign material from the grain. A winnowing machine can be used where available.
Parboiling is done by suspending a jute bag full of rice over steaming water in a drum or tank to break up the bran covering the paddy. The paddy is soaked in hot water at a temperature of about 70oc for five hours. Empty grains are skimmed off. It is then boiled for 10-15 minutes.
Parboiling is stopped when bran begins to split open. White centre or chalky grains are signs of incomplete parboiling, such grains break during milling.
6. Drying and Tempering:
Dry in the sun to 16% moisture content then to 13-14 moisture content under shade and keep for 2 days before milling.
Rice is milled in two stages;
The first stage is DEBARNING or HULLING, this is when the bran covering the paddy is removed.
The second stage is when the rice is polished.
After all these operations are successfully carried out, the rice and now be packaged and stored for consumption.