Tipos de arroz y estructuras

Section 2 Types and Structures of Rice

The history of rice cultivation can be traced back to 12000~16000BC in Hunan of China. After its widespread plantation in China, rice was gradually spread westward to India and then to Europe in Middle Age. Nowadays, except for Antarctic, rice is grown all over the world and feeding half of the world population, it has become the major food crop in the world.

1. Classification of rice and its characteristics

Based on the grain shape and quality, rice can be classified into the following three types.

• Indica rice

Indica rice is heat resistant and strong light proof. Its grain is normally slender or in long oval shape, with low strength and thus poor resistance to pressure. As it’s likely to produce broken rice during processing, its rice yield is low. When boiled or steamed, its viscosity is small but expansion rate is big.

• Japonica rice

Japonica rice is cold resistant and weak light proof. Its grain is generally in oval shape, with high strength and good resistance to pressure. Unlike indica rice, japonica rice is unlikely to produce broken rice during processing, and thus has higher rice yield. When boiled or steamed, its viscosity is big but expansion rate is small.

• Glutinous rice

Glutinous rice grain is normally milky white, opaque or semi-transparent. And like japonica rice, when boiled or steamed, its viscosity is big but expansion rate is small.

As per grain quality and harvesting season, rice can also be divided into early rice and late rice. As their names indicate, early rice has shorter growing period and is harvested early while late rice has relatively longer growing period and is harvested late. Besides, early rice and late rice have totally different qualities. Early rice is much loose and has poor resistance to pressure, thus it’s more likely to produce broken rice during processing and has low rice yield. While the opposite is true for late rice. And for the same type of rice, the quality of late rice is better than that of the early rice. When boiled or steamed, late rice also excels in edible quality. For different types of rice, let’s take early japonica rice and late indica rice for example, the latter is still superior to the former in terms of quality.

2. Structure of rice grain

Rice grain is composed of two parts, namely, glume and caryopsis.

• Glume

The glume of the rice grain is mainly for protecting the caryopsis. After the rice grains go through the rice husker, the glume will fall off and the fallen glume is called husk. Generally speaking, the mature and plump rice has thin and light glume. The japonica rice has thinner and lighter glume than the indica rice and is more easily husked. For the rice that has not reached maturity, its glume is more elastic and tenacious, thus hard to be removed.

• Caryopsis/husked rice

After the glume is removed, the caryopsis remains, also called husked rice. Husked rice consists of three parts: bran, endosperm and germ. Normally during rice milling, the bran shall be partially or fully removed. The rice bran takes up about 5.2% up to 7.5% of the whole rice grain in terms of mass.

• Endosperm

Endosperm is the major component and its mass occupies up to 70% of the total mass of the whole rice grain. Endosperm is tightly wrapped inside by the bran and composed of starch cells. If the starch granules are filled with protein and have no gap left, then the endosperm structure will be compact and hard. And the rice grain will be semi-transparent and its cross section will be smooth and flat. This type of endosperm is called cutin endosperm. On the other hand, if there are gaps among starch granules inside the cells, then the endosperm structure is incompact and the rice grain is opaque with coarse and lime-like sections. The endosperm in this case is called farinaceous endosperm.

• Germ

Germ is located in the lower abdomen of the husked rice and contains plenty of unsaturated fatty acid. Rice with germ is not suitable for long term storage as it’s easy to turn moldy and become bad. As germ is not tightly connected with endosperm, thus it can be removed easily during processing.