Why is the endosperm separated from bran and germ to make white flour?

In the production of white flour, the endosperm is separated from the bran and the germ primarily to achieve a specific texture, color, and shelf stability.1

The milling process aims to isolate the starchy endosperm—which constitutes about 85 percent of the kernel—from the outer bran layers and the oily germ. Removing these components results in a lighter-colored, softer grain compared to whole wheat flour, which utilizes the entire kernel.231

Beyond physical characteristics, the removal of the germ is significant for storage; because the germ contains oil, its exclusion helps the resulting white flour preserve longer. The final grade of the flour is determined by the residual amount of branny particles remaining after the gradual reduction process, with the purest "patent" flour being remarkably free from such impurities.4562