Researchers from KU Leuven, Belgium, have developed a new and quicker way to check whether the cocoa butter – the fat in the chocolate – is crystallising correctly during the hardening process, which determines the quality of the chocolate.
Producing bars of chocolate that have a beautiful gloss, make that wonderful sound when you break them, melt in your mouth and maintain all these qualities throughout their shelf-life, is not easy, claimed the researchers.
‘The qualities we want’
“Cocoa butter crystallises as the liquid chocolate hardens,” said Professor Imogen Foubert from the KU Leuven Department of Microbial and Molecular Systems. “Five types of crystals can be formed during this process, but only one of these has the qualities we want.
“The number, size, shape, and the way in which the crystals stick together play an important role as well.”
It is therefore crucial to monitor the crystallisation of the cocoa butter closely during the chocolate production process to avoid inferior chocolate ending up on shop shelves, she added.
“We’ve discovered that we can detect differences in the crystallisation of cocoa butter with ultrasonic waves,” said Professor Koen Van Den Abeele from the KU Leuven Department of Physics and Astronomy.
The new technique involves sending transversal ultrasonic waves through the cocoa butter. The researchers then measure the reflection of these waves for information about the structure of the butter. The technique is similar to the ultrasound echography used to monitor the health and growth of foetuses in the womb.
“When the cocoa butter is liquid, the ultrasonic wave is reflected in its entirety,” added Van Den Abeele. “As soon as the butter crystallises, part of the sound wave penetrates the cocoa butter, so the amount of reflection we measure changes. This enables us to see how the different crystals stick together, which is important for the ultimate properties of the chocolate.”
Chocolate manufacturers currently check the quality of their chocolate ‘offline’. A sample is taken from the production line to be analysed in a lab. This method is very time-consuming, making it impossible to intervene quickly when something is wrong. As a result, a large amount of chocolate is wasted or re-processed, which is very costly.
Online scan is quicker
In contrast, the novel technique developed by the researchers can be used to check the chocolate while it’s still on the production line.
They have designed a lab prototype, which now needs to be turned into a prototype for use in real chocolate production lines.
The findings were the result of Annelien Rigolle’s interdisciplinary doctoral research, supervised by Foubert, who specialises in fat crystallisation, and Van Den Abeele, who is an expert in the use of ultrasound for non-destructive testing of materials such as composites, metals, and concrete.