Process : washing- grinding-remove egg membrane with washing (have to repeat this washing process many times )-dry-grinding-fine grinding-sterilization-packing
This method is punctuated with repeated washing process for many times. It is essential process so as to remove the egg membrane and any other protein in goods.
Grinding and washing method is peeling out egg membrane from egg shells by specific gravity in water. So using this method is needed much water and time. This method is not cheap.
Finally you have to dispose of this black water. It also needs much cost.
If you dispose the black water by a lawful way, it also cost you a lot.
If you do these processes sometimes there are still left some egg membrane or any other protein.
As a final drying process, in this method is needed to use sterilize with hot blast.
But some bacteria have tolerance for heat so that you cannot remove bacteria perfectly.
If you want perfectly remove the bacteria, it is needed high temperature. But in high temperature, egg-shell powder's color can be changed. In eggshell calcium rating, 'whiteness' is very important. It is dilemma.
If you dispose the black water illegally, grinding and washing method can be cheap and easy way to make the goods.
This is the reason why the most of the factory choose the grinding and washing method.