noun
rice polisher; rice polishing machine
A machine that polishes rice, removing the bran layer to produce white rice. Common in agricultural and food-processing contexts.
この工場では研米機を使って玄米を白米にしている。
In this factory, they use a rice polisher to turn brown rice into white rice.
Compound of 研 (polish, sharpen), 米 (rice), and 機 (machine). The exact historical derivation is uncertain, but the components transparently describe a rice-polishing machine.