Cocoa powder is obtained from the dark and bitter cocoa paste or cocoa liquor after being pressed. The pressing of the cocoa removes about three-quarters of its oil or cocoa butter and what remains is called cocoa cake, about five centimeters thick. These cakes are crushed into fine cocoa powder.
What follows is a simplified example of the process
The raw cacao beans are fermented and dried after which the beans are roasted, winnowed and cracked giving us our "nibs." The nibs are ground to transform into a paste which is referred to as a chocolate mass or chocolate liqueur. The consistency of this chocolate liqueur is very thick and contains about half cocoa butter and half solids depending upon the specific bean. This chocolate liquor is not yet what we really think of as 'chocolate but it is the "essence" of chocolate in its the purest form.
This chocolate liqueur is then placed in clean cotton or other natural fabric which is placed inside of a mold with holes—now the chocolate liqueur is ready to be pressed. The fabric contains the cocoa mass leaving the cocoa butter to filter out as the weight of the press pushes down. The solid mass or cocoa cake that remains in the cloth will be crushed into fine cocoa powder.