Moisture migration will quickly ruin incompatible water-containing centers layered side by side in a candy bar. All of the moisture migration in an enrobed layered bar will be internal; that is, the movement of water will be from the center or inclusion with the higher free-water content into the center or inclusion with the lower free-water content. The unhappy result of moisture migration is the diminished quality of each center or inclusion: one is drier than it should be because it has lost moisture and the other wetter than it should be because it has picked up moisture. Further, moisture migration into noncrystalline sugar-based centers will induce those centers to crystallize, inexorably altering their texture. When a high-moisture center like ganache is layered with a center that is hygroscopic, like soft caramel, the caramel absorbs moisture from the ganache, unless steps are taken to prevent it. The same is true when inclusions that are likely to absorb moisture, such as cereals or baked cookie dough, are used with a high-moisture center like ganache. Combinations like these will last only hours or days before the inclusions soften and the quality becomes unacceptable. While the best practice is to simply avoid these combinations, moisture migration can be limited or prevented by placing a layer of fat between two incompatible parts of a bar. In the case of the caramel and ganache combination, brushing the caramel with a film of cocoa butter before pouring on the ganache will greatly prolong the life of the bar. In the case of the hygroscopic inclusions, coating them with a thin film of cocoa butter before incorporating them into the center will help to preserve their integrity. The method is helpful but imperfect as a moisture barrier; because most inclusions have a large surface area and are porous, they often do not receive the cocoa butter coating evenly or completely. For more information on moisture migration.