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E12 Staple Foods - Rice
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Planting rice seedlings in Madagascar |
Rice is probably the world’s most important staple crop, providing food for more than 1.6 billion people. Over 600 million people derive more than half of their calories from rice. Its importance has been recognised for many centuries - in India it was once known as "dhanya" meaning "the sustainer of the human race".
The major rice crop is Oryza sativa. There are many different cultivars of which the two most important forms are "indica" and "japonica". The "indica" form produces long-grain rice and is grown in tropical areas such as South-East Asia and the Philippines whilst the short-grained "japonica" form is cultivated in temperate areas including Japan and northern China. Another species, Oryza glaberrima, is cultivated on a much smaller scale in Africa. Wild rice is produced from an entirely different species - Zizania aquatica - and is harvested from wild plants in North America.
Where did rice originate?
Although rice has been cultivated in Asia for several thousand years, it is not clear where it originated although some botanists consider India or South-East Asia to be the most likely areas. It arrived in South China very early and then spread south through the Malay archipelago to Indonesia and the Philippines. The crop was transferred from China to Japan about 100 BC and was probably taken to Madagascar by the Malays. The Portuguese probably introduced it to South America through Brazil.
The world’s largest producers of rice are China (172 million tonnes), India (102 million tonnes) and Indonesia (42 million tonnes) (figures for 1988). Brazil is the largest producer of rice outside Asia. Rice is also an important staple in parts of Africa including Madagascar, Senegal, Gambia and Tanzania. A small amount of rice is grown in Europe, principally in Italy, Spain and Portugal.
How is it cultivated?
Rice thrives over a wide range of climatic conditions between latitudes 45° north and south of the equator. Its most important characteristic is its ability to grow in water. Its specialised stem anatomy with large air spaces allows oxygen to reach the roots in waterlogged soil. This has permitted the cultivation of the extensive flood plains of Asian rivers such as the Ganges, the Irrawaddy and the Mekong.
Most of the crop is grown as wet rice (also known as swamp or paddy rice) on land inundated by flooding, either during the rainy season or by controlled irrigation, or on natural swamp. This form of rice cultivation allows the land to be used almost continuously, permitting the development of a dense human population. It relies on the supply and control of water during the growing period, which is achieved by means of bunds (raised mud barriers) around the boundaries of the paddy fields. An important feature of this method of cultivation is that it reduces soil erosion. Fish are raised in the flooded paddy fields to supplement the diet.
Much rice cultivation in the tropics depends on the monsoon, when there is ample rainfall and land preparation is easier. In India rice is planted during the South-West monsoon between the end of May and the middle of October. However, the arrival and duration of the monsoon rains are often unreliable, with catastrophic effects on the rice crop.
Rice plants are usually sown in a nursery field and then transplanted as seedlings to a well-soaked field with a small amount of standing water. The depth of water is increased as the crop grows and then reduced prior to harvest. Because the soil is flooded, there is little decomposition of organic matter to provide nutrients, but nitrogen is fixed by micro-organisms in the water, such as Azotobacter and cyanobacteria.
Upland rice, grown on 10 per cent of the total rice-crop area, is cultivated where rainfall is adequate. It is a staple crop for the Iban people of Sarawak who practise a form of shifting cultivation. Floating rice is cultivated in areas of deep flooding such as eastern Pakistan, Vietnam and Burma, where water levels rise to 5 m or more. The rice stems grow rapidly, keeping pace with the rising water.
Most cultivation is carried out by small-scale farmers and is a very labour intensive process, because many of the operations are carried out by hand.
Nutritional value
Like all cereals, rice supplies energy (both as carbohydrates and oils), proteins, minerals, vitamins and fibre in the diet. It is better nutritionally than other carbohydrate staples such as yams and cassava, although it lacks some essential amino acids. Its nutritional value depends very much on the processing it undergoes.
After harvesting, rice is threshed and winnowed to separate the grain from the husk. The resulting brown rice is milled and polished to remove the outer layers of the seed and produce white rice. This is just the central part of the grain and contains only starch. The outer layers of the seed contain proteins, oils, vitamins and fibre so brown rice is of higher nutritional value than white rice. The disease beri-beri was first detected in people who had introduced polished white rice into their diets in place of brown rice. It is caused by a lack of vitamin B1, which is lost during the removal of the outer seed layers, and results in loss of muscle tone due to nerve inflammation.
By parboiling the rice before it is milled, vitamins are driven into the centre of the grain thus increasing the vitamin content of white rice. Some forms of rice are fortified by spraying vitamins onto the polished rice.
Different types of rice
Different cuisines around the world prize different types of rice. Most savoury dishes are accompanied by long-grain hard rice, which has dry separate grains when cooked. Short-grain rice becomes creamy when cooked and is used in milk puddings and risottos. In Japan and Korea, glutinous rice is preferred because it is sticky when cooked and is easier to eat with chop-sticks. It is used for special savoury dishes and cakes. In India, the aromatic basmati rice is very popular; the word basmati means fragrant.
Parched rice, rice flakes and puffed rice are produced by heating the grains in different ways. For example, rice heated under pressure expands forming puffed rice which is popular as a breakfast cereal or in rice cakes. Ground rice made from broken grains is used in confectionery. Rice flour is used to make cakes and noodles. It is so soft that it can also be used as a base for face powders and eyeshadows. Beers, wines and spirits are made from fermented rice - in Japan the production of saki, a rice wine that is drunk hot, uses 5 per cent of the country’s total production.
Among the by-products of rice processing are the husks which are used as a fuel and as an aggregate for light-weight concrete. Rice straw is used to make strawboards, for thatching and braiding and as an animal fodder. It is also the substrate for the cultivation of the straw mushroom (Volvariella volvacea).
"Green Revolution"
In the 1960s, the so-called "Green Revolution" occurred, with the development of high-yielding rice cultivars capable of responding to higher inputs of fertiliser, irrigation, fungicides and machinery. However, it had numerous unforeseen social consequences. Much of the requisite technology proved too expensive for small-scale farmers and increased mechanisation resulted in a loss of jobs. In some areas, disease has devastated the new cultivars. The new cultivars replaced older diverse forms with their resistance to disease and tolerance of adverse conditions, leading to a loss of genetic resources for future rice-breeding programmes.
Further information
Grist, D. H., 1986. Rice, 6th ed., Longman
Rehm, S. and Espig, G., 1991. The Cultivated Plants of the Tropics and Subtropics, Verlag Josef Margraf
Purseglove, J. W., 1968. Tropical Crops: Monocotyledons, vol. 2, Longman
Max Paris, Breeding Rice. McGill University.