Science Why does chocolate ever know?

When chocolate forms a white veil on its surface, it causes confusion among many consumers. "The fat bloom is completely harmless, but leads by rejects and claims to millions of damages in the food industry," explains Svenja Reinke of the Technical University of Hamburg-Harburg (TUHH). She is the lead author of a joint study by scientists from the Technical University of Hamburg-Harburg (TUHH), the Research Center DESY (German Electron Synchrotron) and the Nestlé Research Center for Confectionery for the development of the white fat on chocolate. The researchers published their results in the journal "Applied Materials and Interfaces" of the American Chemical Society.

The current study, according to the researchers, "provides new insights into the formation of the unwanted fat bloom, which sometimes deposits as a white layer on the chocolate." Although this is completely harmless, "although the fat does not represent spoilage of the product in the true sense, The resulting visual impairment can lead to a large number of consumer complaints, "explains Professor Stefan Palzer of the food company Nestlé. Not infrequently, consumers consider this to be mildew or evaluate it as an indication of an expired shelf life. The fat bloom is therefore "still the most important quality defect in the confectionery industry," says Palzer. But until now, according to Svenja Reinke, relatively little was known about its origins.

Liquid fat migrates to the surface
The fat bloom occurs when liquid fat (such as cocoa butter) migrates from the interior of the chocolate to the surface where it crystallizes, explain the scientists. This could happen, for example, when liquid chocolate cools uncontrollably and forms unstable crystal forms, "but even at room temperature, a quarter of the chocolate fats are already liquid," says Reinke. Liquid fillings or parts such as nougat will additionally accelerate the formation of fat bloom. "The longer the chocolate is, the more time fat has to travel through the chocolate", which is why the white spots are often perceived as a sign of old chocolate, reports the TUHH.

Researchers X-ray chocolate
In their investigations, the researchers were able to use a special X-ray method to observe live the underlying processes in the formation of white fat on chocolate. Samples of individual chocolate components, for example, a mixture of sugar and cocoa butter or milk powder and cocoa butter or cocoa and cocoa butter, were ground to a fine powder and then transilluminated with the bright X-ray, according to the TUHH. "The examination technique shows us both the fat crystals and the pores down to a size of a few nanometers," reports study leader Professor Stefan Heinrich from the TUHH.

Changed structure of chocolate
To study the fat migration within the chocolate, the researchers each dripped some sunflower oil onto their samples and observed the consequences. According to Svenja Reinke, it was "within seconds for wetting" and the oil penetrated "very quickly in the smallest pores, probably by capillary forces." By adding the sunflower oil has also changed the internal structure of the chocolate, the liquid fat dissolved over a period of hours further fat crystals and thus the entire structure of the chocolate was softer. This in turn led to an increase in fat migration, reports Reinke.

Investigation of structural changes
According to the researchers, the exact sequence of these processes was not yet known and the current study complements earlier studies on the crystal structure in the fat bloom. For the first time, the dynamic mechanisms that lead to the formation of the fat bloom are directly comprehensible in detail. "The joint study provides us with valuable information, as we have structural changes in such common Investigate multicomponent systems, "explains Dr. Stephan Roth from the DESY Research Center.

Approaches to avoid the fat bloom
Based on the current findings, the researchers believe that concrete approaches for the reduction of the fat bloom can be derived for the food industry. "One consequence, for example, would be to limit the porosity of the chocolate during production so that the fat migrates more slowly," reports Svenja Reinke. Furthermore, the limitation of the liquid content by a cool, but not too cold storage, opportunities to minimize the formation of the fat bloom. "18 degrees Celsius are ideal," says Reinke. Overall, chocolate is very sensitive to temperature fluctuations. Here a few degrees would already make a big difference. "At five degrees, the entire cocoa butter is basically solid, but from about 36 degrees, everything is liquid," explains the researcher.

Crystal shape of the chocolate is also important
According to the scientists, the crystal form in chocolate also plays an important role in the formation of the fat ring. In this case, chocolate basically has six different crystal forms, which also exert an influence on the liquid content. This offers manufacturers another way of minimizing fat bloom. "The studies carried out allow us, as a manufacturer of quality chocolate, for the first time to draw conclusions about the causes of the migration of cocoa butter fractions into chocolate," concludes Professor Palzer. (Fp)