Brown rice flour is nothing more than brown rice grains ground to a powder. The challenge is that rice is difficult to grind into a smooth flour. Even carefully ground rice can be gritty, like meal, rather than smooth, like flour. To grind rice to a smooth flour, you must have the right tools: either a powerful blender or a home grain mill. Coffee grinders and standard blenders can make rice meal, but they will not give you smooth flour.
Measure 1 cup of brown rice into a high-speed blender. Put the lid on the blender.
Turn the blender on to a "Medium-High" setting.
Scrape down the sides with a rubber spatula, if necessary.
Listen to the sound of the rice hitting the sides of the blender. The tinkling sound of bits of rice striking glass or metal will become quieter when the rice is reduced to a powder.
Place the rice in the hopper of your grain mill.
Set the grinder to "Medium" and grind the rice into a coarse meal.
Put the meal back into the hopper.
Set the grind to "Fine" and grind the meal into a flour.
By nature, rice flour gives baked goods a grainier texture. Substituting rice flour for wheat flour in baked goods produces products with a drier, finer crumb. Rice flour also does not create the structure that gluten strands create in baking. If your rice is not coming out as finely as you'd like, soak the rice in water overnight, drain it in a strainer and then spread it out on parchment paper to dry completely before grinding.