The grade is defined by how well the rice is polished. For the sake fermentation, the starch, which is the main nutrient of rice, is necessary, however, other nutrients like proteins, fat, and vitamins are contained in rice.

Normally those nutrients are not directly necessary for fermentation, however, they can produce a variety of flavors and add thick layers of taste. Sake brewed with highly polished rice tends to have aromatic and smooth taste, and it is also more expensive and quantity is limited. Less polished rice makes for more complex and full-bodied sake.