Rice is a kind of grass species that has been cultivated to produce the most important food grain in the world. A fifth of the energy of the world's humans comes from eating rice.

Rice was first changed from a wild swamp grass to a cereal for eating about 10,000 years ago. This was somewhere in China. The cultivation of rice gradually spread west through Asia and Europe. It was taken to the Americas by European colonists.

There are two types of rice: wet, or paddy, rice and dry rice. Wet rice is grown from seed each year in nurseries, then planted out in paddy (waterlogged) fields, where it grows to about a metre in height. Dry rice seed is planted out in fields like wheat and other cereals.

Paddy farming takes a lot of time and effort. But paddy farming makes it more difficult for other plants (weeds) to grow, and it also keeps a lot of pests at bay.

The seeds of the rice plant are covered with a very hard 'skin', called a hull, husk or chaff. This has to be removed by rubbing it in a mill. This gives brown rice. If the milling is continued,the next layer – the bran – is also removed, together with the germ, and this gives white rice. White rice can be kept longer than brown rice, but when the bran is removed, so are important nutrients and so is a less useful food. White rice can be worked further, polishing it.

Rice can be eaten as boiled, or boiled then fried, grain, or it can be ground into flour. Most white rice is enriched with nutrients, rather like vitamin D is added to wheat flour.

Rice flour does not contain gluten, so it cannot be used to make bread in the way we would use wheat flour. It is usually made into various types of noodles.

Because rice does not contain all of the essential materials for good health, it cannot make up a diet on its own in the way that bread can, and must be eaten with nuts, seeds, beans, fish, or meat.

Rice can be puffed for use as a breakfast cereal, for example. This is done by putting the rice in a low pressure chamber and then raising the temperate for boiling. Puffing increases the size of the rice tenfold.