Scientists X-Rayed Chocolate to Figure Out How it Gets That White Film

By Sarah Zhang on at

Fat blooms, the white stuff you sometimes get on chocolate, have long been the bane of chocolate makers and chocolate lovers. It’s harmless but decidedly unappetising. Now scientists at Nestle have X-rayed chocolate to figure out exactly what’s going on at a microscopic level.

For a ubiquitous sweet, chocolate actually involves some pretty finicky chemistry. The cocoa butter in chocolate forms a crystal structure—more accurately, it can form six different crystal shapes, only one of which gives chocolate the smooth, glossy finish we all like. You can only get that specific crystal shape by heating and cooling the chocolate a specific way, a process called tempering. Improper tempering is one reason behind fat blooms.

Basically, fat blooms happen when chocolate lacks or loses its specific crystal structure, and fat migrates to the surface of the chocolate. But how this process happens on a microscopic level has been more of a mystery.

That’s why researchers decided to train X-rays on a powdered mixture of cocoa, sugar, milk powder and cocoa butter aka the main ingredients of chocolate. (The powdered form sped up the process, allowing the team to observe it in real time.) Then, they added some liquid oil, which quickly spread through the mixture via capillary action and dissolved the solid cocoa butter. The now liquid cocoa butter lost its crystal structure, leading to blooming.

The researchers conclude that the more porous a chocolate bar is, the more prone it is to blooming. Keeping chocolate cool also helps it keep its crystal structure. Next time you bite into a chocolate bar, think about how much chemistry went into making it.

[ACS Appl. Mater. Interfaces]

Top image via European Synchrotron