The grains of rice are called caryopsis in botany and are customarily called seeds. From the outside to the inside, they include the caryopsis, pericarp, seed coat, aleurone layer, endosperm and embryo. .

The outside of rice seeds is surrounded by glomes (rice husks). The glomes are divided into inner globules and outer glomes. The outer globules are larger and the inner glomes are smaller. The edges of the two are connected with each other, which is the protective structure of brown rice. Some varieties also have long or short awns on the outer globules. The presence, length and color of awns also vary from variety to variety and are one of the basis for identification of rice varieties.

Brown rice is obtained after peeling off the chaff from the grain. Brown rice can be divided into three parts: testa, endosperm and embryo. The surface of the testa is the pericarp, which is developed from the ovary wall. Inside is a very thin layer of seed coat developed from the ovary integument, and the interior is endosperm tissue.

The outer layer of the endosperm is the aleurone layer. 98% of the weight of brown rice is endosperm, which is rich in starch and a small amount of protein, fat, etc. It is the main part of human consumption and is also the source of nutrients for rice seed germination and seedling growth in the early stages.

The volume of the embryo accounts for about 3% of the grain. When the embryo is damaged, the rice seed cannot germinate. The embryo is mainly composed of four parts: scutellum, embryo, hypocotyl and radicle, and is the embryonic body that develops into seedlings. When a seed germinates, the radicle grows downward and develops into a seed root, and the embryo grows upward and develops into the above-ground part of the seedling.

The chaff, testa, aleurone layer and embryo will all be ground away when processing rice, especially when processing polished rice.