noun
degree of milling; milling yield
Technical term used in rice processing to indicate the percentage of the original brown rice remaining after milling; higher values mean less bran removed.
このお米は精白率が90％で、胚芽が残っています。
This rice has a milling yield of 90%, so the germ remains.
精白率が低いほど、白米に近くなります。
The lower the degree of milling, the closer it is to white rice.
歩留まり is a broader term for yield or recovery rate in manufacturing, whereas 精白率 is specifically for rice milling.
Compound of 精白 (seihaku, 'polishing, milling') and 率 (ritsu, 'rate, proportion'). The exact historical derivation is uncertain, but the term is a straightforward technical compound.