6th Grade - Social Studies

LESSON PROBLEM: Economics: How is rice prepared for milling and commercial processing?


The process of separating the rice grain and straw is called threshing. Threshing can be done by hand, or by machines. Rice farms in the United States use a combine to harvest and thresh the rice. These are large machines that go through the field cutting and separating the grain from the straw. That is why it is called a combine. Because it "combines" the two steps into one. it can efficiently harvest many acres quickly.

In small rice growing communities found in less developed countries rice is harvested or cut by hand with a knife-like tool and is then dried. After that, it is carried back to the village to separate the straw, consisting of the plant and stems, from the grain.

Hand Threshing
There are several methods used for hand threshing. Sometimes, the sheaves which are bundles of rice plants with the grain still attached are beaten against stones, a log, a special threshing ladder, or a simple wood board. The grains are shaken loose from the stems, which are called panicles and fall into a container. In some countries, as in India and Burma, sheaves are laid out on threshing floors, and trampled on by domestic animals. On the island of Bali, rice is threshed by beating it against slats of bamboo.

Simple Threshing Machines
Simple threshing machines are also used. They are powered by hand, foot, or gasoline engine. These machines make the job of threshing much easier and more effective. A pedal-driven machine can usually thresh 100 kg of paddy rice in one hour. While a small engine-powered threshe is even more effective.

The process of cleaning the rice is called winnowing. It is done after the grain is hulled or shelled. The paddy rice is collected after threshing to be cleaned. In the United States, the rice grain goes through a series of seives in the winnowing process.

In many countries, the simplest way of winnowing is to shake the rice back and forth on a flat bamboo tray. This separates the grain from the chaff and dust, which collect at the end of the tray. The tray is then tossed to remove this material. It is held high and gently tipped down, making the heavier grain fall on a mat, while the chaff is blown away by the wind. The straw-like hull blows away too.

Rice can also be winnowed by gently rocking it in a bamboo sieve. While the grain falls flat on the mat, the wind carries away the chaff. Some farmers also use hand-winnowing machines that have a fan driven by a handle. The paddy rice is fed into the moving hopper, which drops it in front of the draft created by the fan. The chaff is blown away by the draft, while the heavier grain falls close by.

Drying the Rice
After threshing and winnowing, the clean rice must be carefully dried before storing it. At the point of harvesting, rice has a moisture content of 18-25%. This moisture content must be reduced to 14% and below, otherwise the rice would rot. In the U.S., rice is dried and stored in clean, storage silos where temperature and humidity controlled air is blown through the rice. In other drying methods, hot air is blown through piled sacks of grain. This method is quick and protects the rice from being spoiled by a sudden rain. In less modern countries, the traditional method of drying rice is to spread the grain on mats, earth floors, or concrete floors in the sun. It is raked over to ensure that it dries evenly.

Storage of Rice In the United States
Once the combines have cut and separated the grain from the stalk, the grain is pumped into trucks which transport the grain to the drying and storage facilities. Here the rice is stored at precise moisture levels to keep the grain at peek quality until it is ready to mill.

Modern methods involve storing the rice in steel and concrete silos, which automatically control humidity and temperature. After storing the paddy rice, it is either milled or commercially processed before being sold.

In many countries rice is stored in a way to protect it from damp, heat, rodents, insects, birds, and fungi. It is often kept in large pots, or waterproof bags, and is stacked either in lofts or in barns built on stilts. In Sri Lanka, paddy rice is stored in a bissa. This is a container made from tough jungle creepers, plastered with clay and lime. In Pakistan, farmers use large earthen pots, which are 3-4 meters high. They are sealed with clay.


Visit a farm during the harvesting season and note your observations.


Study the process of threshing and winnowing other grains, particularly wheat and compare the process with that of rice.

  • rake
  • sheaf
  • silo
  • winnowing

Click here to play Rice Rampage!
American Rice:
More than 90% of the rice eaten in the United States is grown by U.S. farmers.
Click here to learn more about where Rice is grown in the United States.
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