Soon it will be Christmas Eve. And while the bells have never sounded sweeter, sweet temptations are rarely more enticing... Chocolate angels, domino pieces, and pralines accompany the countdown. Brain food for the pre-Christmas tension arc. Thank you, chocolate!
But oh, horror! What if the beautifully packaged, pleasure-promising praline suddenly doesn’t look so pretty once unwrapped, but is covered with a whitish-gray film? Is the praline spoiled? Has mold formed on its surface? Has its expiration date long passed?
Research Cooperation Helps Understanding
What is going on with the chocolate? As with so many questions that move us in life, an institute at TU Hamburg can explain. Although not specialized in chocolate, the Institute under the direction of Prof. Stefan Heinrich focuses on Solids Process Engineering and Particle Technology (SPE). The good news first: the institute’s senior engineer, Dr.-Ing. Swantje Pietsch-Braune, can give the all-clear and wishes you a good appetite. "Because such a coating neither changes the taste nor is harmful in any way. It is purely a visual phenomenon." A phenomenon, however, that causes the chocolate industry millions in damages year after year and is considered one of the great problems of the food industry. Reason enough for SPE to take a closer look at the subject: the answer is "fat bloom." Admittedly, not a very appetizing term. The English "fat blooming" sounds more elegant in the vocabulary of chocolatiers.
Oil Simply Migrates
But what does it actually mean? "It is fats that crystallize on the surface of the chocolate," explains Pietsch-Braune. "The fat usually comes from cocoa butter and migrates through the chocolate," she summarizes the central result of the investigations. This process is triggered by various effects, including the so-called capillary effect: small pores in the chocolate, caused for example by cocoa powder, allow the fat to migrate through the chocolate, which is referred to as capillary-driven fat migration. "In addition, there is a chemical dissolution or recrystallization of the fat. And these crystals can then be seen on the surface of the chocolate." In an earlier study, sunflower oil was applied to chocolate and it was possible to observe live how the oil was drawn into the chocolate within seconds to minutes, she reports.
Varieties, Temperature, and Storage Duration
The porous structure of the chocolate opens the way for the fat. "Whether this occurs or not also depends on the temperature, because chocolate can exist in different crystal forms. At higher temperatures, the liquid components increase, promoting the migration process," says the particle technologist. But also a liquid or particularly fat-rich core, such as nougat inside the chocolate, as well as longer storage times favor the process or at least increase its likelihood. By the way: dark chocolate, often touted as healthier due to its higher cocoa and thus fat content, is particularly prone to fat bloom.
Conclusion: The combination of storage duration at elevated temperatures favors—depending on the variety—fat blooming. Scientific recommendation: Don’t store chocolate for too long, but enjoy it soon!
