Relationship between chocolate microstructure, oil migration, and fat bloom in filled chocolates

Fat bloom is one of the main quality problems in the chocolate industry. A bloomed chocolate product is characterized by the loss of its initial gloss and the formation of a gray‐whitish haze, which makes the product unappealing from a consumer point of view. In the industry, most of the fat bloom related problems arise in filled chocolate products, like pralines and chocolate‐coated biscuits. In these products, oil migration is considered the main cause of fat bloom development. It leads to the dissolution of solid cocoa butter crystals in the chocolate shell which may recrystallize with the formation of undesired crystals. These give rise, upon growth, to visual fat bloom. When looking at the available literature, most of the studies elucidate the possible mechanisms of oil migration and the subsequent fat bloom formation using model systems. These model systems are sometimes too distant from the real industrial applications and the important role of the microstructure of the products are often neglected, although it plays a crucial role in migration‐induced fat bloom development. The main objective of this review is to describe the relationships between chocolate microstructure, oil migration, and fat bloom. Practical applications: This review can be used as a base for the development of microstructural strategies to retard oil migration and fat bloom development in filled chocolates. An important strategy to retard oil migration and migration‐induced fat bloom is the creation of more dense structures. By creating denser structures, the overall mobility is reduced leading to a decrease in the rate and extent of oil migration. Also, more dense structures hinder recrystallization and Ostwald ripening, thereby delaying the migration‐induced fat bloom development. As fillings are less standardized and not bound by legislation, modification of the filling composition and microstructure offers more opportunities in delaying fat bloom. The main objective of the review is to describe the relationships between chocolate microstructure, oil migration, and fat bloom, as illustrated in this scheme. The numbers indicate the four parts that are discussed in this review.