Even in a strong blender like a Vitamix (highly recommended) you need to blend it for a bit to get a smooth consistency. So it's not a case of blending it as long as it takes for the ingredients to combine, you need to keep blending until it's really smooth. So be patient, stop and scrape down the sides of the blender and then blend again. Then check the texture. When there is no graininess at all, then you know you're done.