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Domesticated rice comprises two species in the Poaceae (“true grass”) family, Oryza sativa and Oryza glaberrima. These plants are native to tropical and subtropical southern Asia and southeastern Africa. Rice provides more than one fifth of the calories consumed worldwide by humans. (The term “wild rice” can refer to the wild species of Oryza, but conventionally refers to species of the related genus Zizania, both wild and domesticated.) Rice is a monocarpic annual plant, growing to 1–1.8 m tall, occasionally more depending on the variety and soil fertility. The grass has long, slender leaves 50–100 cm long and 2–2.5 cm broad. The small wind-pollinated flowers are produced in a branched arching to pendulous inflorescence 30–50 cm long. The seed is a grain (caryopsis) 5–12 mm long and 2–3 mm thick.
Rice is a staple for a large part of the world’s human population, especially in East, South and Southeast Asia, making it the most consumed cereal grain. Rice cultivation is well-suited to countries and regions with low labour costs and high rainfall, as it is very labour-intensive to cultivate and requires plenty of water for irrigation. Rice can be grown practically anywhere, even on steep hillsides. Although its species are native to South Asia and certain parts of Africa, centuries of trade and exportation have made it commonplace in many cultures.
The seeds of the rice plant are first milled using a rice huller to remove the chaff (the outer husks of the grain). At this point in the process the product is called brown rice. This process may be continued, removing the germ and the rest of the husk, called the bran at this point, creating white rice. The white rice may then be buffed with glucose or talc powder (often called polished rice, though this term may also refer to white rice in general), parboiled, or processed into flour. The white rice may also be enriched by adding nutrients, especially those lost during the milling process. While the cheapest method of enriching involves adding a powdered blend of nutrients that will easily wash off (in the United States, rice which has been so treated requires a label warning against rinsing), more sophisticated methods apply nutrients directly to the grain, coating the grain with a water insoluble substance which is resistant to washing.
Despite the hypothetical health risks of talc (such as stomach cancer), talc-coated rice remains the norm in some countries due to its attractive shiny appearance, but it has been banned in some and is no longer widely used in others such as the United States. Even where talc is not used, glucose, starch, or other coatings may be used to improve the appearance of the grains; for this reason, many rice lovers still recommend washing all rice in order to create a better-tasting rice with a better consistency, despite the recommendation of suppliers. Much of the rices produced today are water polished.
Rice bran, called nuka in Japan, is a valuable commodity in Asia and is used for many daily needs. It is a moist, oily inner layer which is heated to produce an oil. It is also used in making a kind of pickled vegetable.
The raw rice may be ground into flour for many uses, including making many kinds of beverages such as amazake, horchata, rice milk, and sake. Rice flour is generally safe for people on a gluten-free diet. Rice may also be made into various types of noodles. Raw wild or brown rice may also be consumed by raw foodist or fruitarians if soaked and sprouted (usually 1 week to 30 days).
The processed rice seeds are usually boiled or steamed to make them edible, after which they may be fried in oil or butter, or beaten in a tub to make mochi.
Rice, like other cereal grains, can be puffed (or popped). This process takes advantage of the grains’ water content and typically involves heating grain pellets in a special chamber. Further puffing is sometimes accomplished by processing pre-puffed pellets in a low-pressure chamber. The ideal gas law means that either lowering the local pressure or raising the water temperature results in an increase in volume prior to water evaporation, resulting in a puffy texture. Bulk raw rice density is about 0.9g/cm³. It decreases more than tenfold when puffed.