Updated: Mar 13, 2021
The rice that is used to brew sake is normally polished in order to get rid of some unnecessary components in the outer and middle layers. It is the pure starch (Shinpaku) in the middle that is most wanted for sake brewing.
In general, the bigger the proportion of its original size being polished away, the better the grade/quality of sake. This leads to a finer and purer taste in the resulting sake. For example, sake with 60% polishing rate means that about 40% of the rice’s outer layer has been milled away.