Fat free cocoa solids is the nonfat component of chocolate. When sold as an end product, it may also be called cocoa powder, cocoa, and cacao. In contrast, the fatty component of chocolate is fatty cocoa solids (cocoa butter).
The separation of the two components may be accomplished by a press. The resulting powder, sold as natural cocoa powder, is more reddish than the traditional "chocolate" color, and relatively low in pH, causing a sour or acidic taste. Dutch process chocolate has been treated so as to neutralize the acidity and has a milder flavor; it is also the traditional chocolate brown in color. Recipes where there is a lot of fat and/or sugar, such as chocolate brownies, benefit from the more intense flavor of natural cocoa, but some prefer the milder taste of Dutch process cocoa in applications such as chocolate milk or hot chocolate.
Fat free cocoa solids are what lends a chocolate bar its characteristic flavor and color, while cocoa butter is what provides smoothness and a low melting point. Also, fat free cocoa solids are what contain most of the antioxidants associated with chocolate. Accordingly, health professionals recommend consuming chocolate in forms that are high in fat free cocoa solids while low in cocoa butter, such as hot cocoa.
Fat free cocoa solids also contain the greatest concentration of the psychoactive chemicals caffeine and theobromine, which are mostly absent in the other half of chocolate, cocoa butter.