My first approach to get grains smaller than 2mm from the mix coming out of a blender was to use a DIY sieve. The second one is a mixture of sieving and grinding:

The solution is made of 3mm steel with a 8.5mm hole drilled and a 8mm threaded rod.

The steel plate with a hopper is mounted on the base plate and the threaded rod is in the chuck of a drill press. By moving the drill up and down WITHOUT the drill rotating, the grains are forced down through the hole. Even at the highest point, the threaded rod is still in the hole of the steel plate, so that only grains of a certain size, fitting in the gap between threaded rod and hole can be squeezed through. Larger grains will get crushed by this process, so that this is a combination of sieving and grinding.

Of course, the raw material filled into the hopper must first be crushed into small pieces with a blender. The advantage is, that larger particles coming out of the blender can also be processed in one run. There is no need to put the large granules back into the blender.