Moisture migration can be an intrinsic factor in mitigating the shelf life of confections, particularly when two or more types of centers are mixed within an enrobed confection. (Moisture migration can also affect unenrobed confections if they are not well protected by packaging. See Environmental Factors Affecting Shelf Life.) Under this circumstance, if the Aw of the centers is not equal, the free water can move from the higher-level center into the lower-level center, altering the texture of each. This scenario can lead to unwanted crystallization of amorphous centers; for example, caramel can crystallize if it absorbs moisture from an incompatible center. If, however, one of the centers is a fat system, like gianduja, it will not absorb moisture from the other center. Internal moisture migration may be prevented by creating a layer of fat, such as cocoa butter, between the two centers to act as a barrier to water movement.