Science: Why does the chocolate turn white at some point?

Science: Why does the chocolate turn white at some point?

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Deciphered formation of white veil on chocolate

If chocolate forms a white veil on its surface, this creates uncertainty for many consumers. "The fat ripeness is completely harmless, but it leads to millions of damages in the food industry through rejects and complaints," explains Svenja Reinke from the Technical University of Hamburg-Harburg (TUHH). She is the lead author of a joint study by scientists from the Hamburg University of Technology (TUHH), the DESY research center (German Electron Synchrotron) and the Nestlé research and development center for confectionery on the development of white fat on chocolate. The researchers published their results in the American Chemical Society's Applied Materials and Interfaces magazine.

According to the researchers, the current study provides "new insights into the development of the unwanted fat ripening, which occasionally deposits on the chocolate as a white layer." Although this is completely harmless, "although the fat ripening does not actually spoil the product, the resulting visual impairment can lead to a large number of consumer complaints, ”explains Professor Stefan Palzer from the Nestlé food group. It is not uncommon for consumers to think that this is mold or that it is an indication of an expired durability. The fat ripening is "still the most important quality defect in the confectionery industry," said Palzer. But so far, according to Svenja Reinke, relatively little was known about the process of its creation.

Liquid fat moves to the surface
The fat matures when liquid fat (such as cocoa butter) migrates from the inside of the chocolate to the surface and crystallizes there, the scientists explain. This could happen, for example, when liquid chocolate cools down in an uncontrolled manner and unstable crystal forms form, "but a quarter of the chocolate fats are already liquid even at room temperature," says Reinke. Liquid fillings or portions such as nougat further accelerate the formation of ripe fat. "The longer the chocolate is lying, the more time the fat has to migrate 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 the underlying processes for the formation of white fat on chocolate for the first time. 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 into a fine powder and then illuminated with bright X-rays, 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 investigate the fat migration within chocolate, the researchers dripped some sunflower oil on their samples and observed the consequences. According to Svenja Reinke, it “wetted within seconds” and the oil “very quickly penetrated even the smallest pores, probably due to capillary forces.” The addition of sunflower oil also changed the internal structure of the chocolate, whereby that liquid fat dissolved more fat crystals over a period of hours and the entire structure of the chocolate became 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 supplements previous studies on the crystal structure in the fat ripe. For the first time, the dynamic mechanisms that lead to the formation of fat ripeness are directly understandable in detail. “The joint study provides us with valuable information on how we can make structural changes in such a way common To examine multicomponent systems, ”explains Dr. Stephan Roth from the DESY research center.

Approaches to avoid fat ripening
Based on the current findings, the researchers believe that specific approaches for the food industry to reduce fat maturity can be derived. "One consequence would be, for example, to limit the porosity of the chocolate during production so that the fat travels more slowly," reports Svenja Reinke. Furthermore, the limitation of the liquid content through cool, but not too cold storage, offers opportunities to minimize the formation of fatty deposits. "18 degrees Celsius is ideal," said Reinke. Overall, chocolate is very sensitive to temperature fluctuations. A few degrees would make a big difference here. “In principle, the entire cocoa butter is solid at five degrees, but everything is fluid from around 36 degrees,” explains the researcher.

The crystal form of chocolate is also important
According to the scientists, the crystal form in chocolate also plays an important role in the formation of fat ripeness. Chocolate basically has six different crystal shapes, which also have an influence on the liquid content. This offers the manufacturers another starting point for minimizing the formation of fat. "For the first time, the investigations carried out allow us as a manufacturer of quality chocolate to draw conclusions about the causes of the migration of cocoa butter fractions into chocolate," concluded Professor Palzer. (fp)

Proof: Espressolia /

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Video: Food Unwrapped: Why chocolate really turns white - News Techcology


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