The process responsible for the white discoloration that sometimes forms on old chocolate can now be prevented after researchers X-rayed tablets of cocoa.
The change in colour, known as fat bloom, is often related to the migration of fats to the surface followed by recrystallisation, but the actual process that takes place and how to prevent it, has never been determined.
German researchers used a micro focus small-angle X-ray to scatter and contact angle measurements to determine the migration pathway of oil into a cocoa butter matrix by using different dispersed particles.
They combined the main ingredients of chocolate – cocoa, sugar, milk powder and cocoa butter – and made them into a powder to speed up the process. Then the scientists used the x-rays to scan into the chocolate crystal structure, down to a scale of several nanometers.
The results showed that the chocolate powders get wet by the oil during the migration process and that the oil is migrating into the pores within seconds. Subsequently, cocoa butter is dissolved by the oil, and thus, its characteristic crystalline structure is lost.
The chemical process triggered by the dissolution is also reflected by microscopic changes of the surface morphology of chocolate model samples after several hours from the addition of oil to the sample.
The study indicated that reducing the porosity of chocolate when it’s being made could help stem the appearance of the off-putting bloom and improve the overall quality of chocolate.
Reducing the amount of liquid fat in chocolate by storing it in cool, but not too cold, conditions would also help, with 18C being the optimum condition.