They do not result from some predetermined pattern in the wind that is somehow impressed on the surface, but rather from the dynamics of individual grains in motion across the surface. (scientificamerican.com)
If using day - old rice, transfer to a medium bowl and break the rice up with your hands into individual grains before proceeding. (seriouseats.com)
They are little individual grains or pellets that vary in colour as you can see from the image. (makeandbakefromscratch.com)