白玉粉 Shiratama-ko
Shiratama-ko is the other widely used glutinous rice flour. Like mochiko, it's made from mochigome rice; however through the special processing its properties are significantly changed: mochi rice is washed, soaked in water and ground very finely in water (in a kind of special mill).The milk white liquid is then pressed, dried and crushed. The flour isn’t a fine powder but coarse granules.
Shiratama-ko was formerly known as 寒晒粉 kan-sarashi-ko. Soaking was always done in very cold water in winter, and without refrigerators this flour could be produced only in the cold season.