Most of the wheat grain and of white flour is made up of starch granules. Starch granules make up about 75% of grain or of white flour. In the processes used to make wheat starch, a small amount of the gluten protein (actually mostly the gliadin fraction, but not entirely), sticks to the surface of the starch granules. The amount depends on the washing method, how many times the granules are washed, and factors like that. Wheat starch can be made very low in surface protein and it is only the surface protein that is of concern (there are some internal granule proteins, but we are pretty sure that they are not gluten proteins).