Making chocolate that melts in your mouth

The smooth versus grainy texture of a piece of chocolate can be due to the amount of open space within the chocolate at the microscopic level, which could change how it melts on the tongue. Smooth creamy chocolate is achieved through a process called tempering, where the chocolate mixture is repeatedly heated and cooled. Improper tempering can result in a grainy mouthfeel, with the particles appearing different on examination. For food manufacturers tempering vast quantities of chocolate, it is vital to understand how that process can affect the taste of chocolate.

Scientists from the University of Guelph at the Advanced Photon Source (APS) located at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have used an X-ray machine to discover the properties of chocolate’s microstructure that provide a pleasing mouthfeel.

Researcher Fernanda Peyronel used a technique called ultra-small-angle X-ray scattering (USAXS) to investigate a property called fractal dimension, a feature of the geometric configuration of tiny particles of chocolate. Researchers were trying to determine whether these particles have a more open or closed structure, correlating that to the mouthfeel experienced by consumers.

The USAXS instrument provides a unique view into the characteristics of chocolate and other materials, as X-ray scattering allows researchers to study a larger volume of material simultaneously, instead of relying on detailed information about a few particles. The X-ray scattering process provides a statistically averaged picture of a much larger region.

“When you’re talking about a chocolate manufacturer that is tempering tons and tons of chocolate, knowing how that process is affecting how the chocolate tastes is very important,” Peyronel said.

Developing a better understanding of the tempering process could lead to major energy and cost savings, as the process requires a considerable amount of time and energy. Previous food science research using the USAXS technique focused on other edible fats, such as cocoa butter. By analysing chocolate as a multi-ingredient matrix containing cocoa butter, cocoa powder, sugar and an emulsifier such as lecithin, researchers hope to develop a greater insight into the relationship between chocolate microstructure and mouthfeel.

“Some chocolate makers want to replace some of the cocoa butter, because this edible fat is quite expensive. However, it’s unclear how the cocoa butter affects the microstructure,” Peyronel said.

While the atomic and molecular structures of chocolate are well known, they are not what consumers experience in their mouths. Instead, a key indicator that has been used to characterise a good chocolate is called a polymorph. The best polymorph, according to researchers, is called βV (beta-5), with a configuration in which the atoms are at their energetic minima.

Researchers are now trying to create a βV polymorph in chocolate that is stable, lending pleasant mouthfeel.

The research was funded by the Natural Sciences and Engineering Research Council of Canada.

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