Characterizing Rheological Properties and Particle Size of Chocolate for Predicting Mouthfeel

Image Credit: Shulevskyy Volodymyr/

Image Credits: Shulevskyy Volodymyr/

Chocolate is one of the world’s favorite snack foods and in 2015, more than $100 billion was spent on chocolate [1]. Chocolate’s appeal lies in its aroma, taste and texture, or mouthfeel. These qualities define the complex flavor of chocolate.

Since the natural ingredients of chocolate differ according to growing conditions, chocolate manufactures do whatever is necessary to ensure that the flavor of their chocolate products is consistent with their signature flavor. As with many food products, customers are strongly loyal to their favorite brands and oppose any changes to the flavor they expect [2]. The signature flavor replicated across batches requires correlation of analytical methods with expensive sensory testing, but it is not possible to taste test every batch that comes from a chocolate factory, however desirable the job might be.

There are various important factors that need to be considered for increasing the chocolate’s appeal. These include:

  • Snap, so there is a first “bite” [3]
  • Melting temperature of 37 °C, so that it melts in the mouth
  • Smooth texture, which gives a nice mouthfeel
  • Shine, so that it looks very appealing

The textural component is essential, because consumers prefer a smooth chocolate to a “gritty” one, and they tend to presume that a smooth chocolate is more luxurious. Extensive consumer testing carried out by chocolate manufacturers over many years has found that particles of cocoa solids, milk and sugar are detected as a gritty mouthfeel at sizes more than 30 µm. The particle grinding methods involved in the manufacturing of chocolate are energy intensive, lengthy and expensive, so large-scale manufacturers optimize their methods to obtain the necessary particle size as efficiently as possible. This optimization is supported by regular particle size measurements, which are carried out by laser diffraction instruments.

Although particles affect grittiness, the flow properties of the fat phase (cocoa butter, which could be mixed with other fats) control how the chocolate coats the inside of the mouth and affects the perception of flavor. The flow, or rheological, properties also have a major impact on the chocolate manufacturing process. Viscosity increases with the reduction of the particle size, and this potentially causes blockages as the liquid chocolate is supplied through the factory. The final product could be a bar, or tablet, of solid chocolate, or the chocolate could be used in an enrobing method to surround a filling centre. Chocolate for enrobing methods is often optimized to obtain good coverage, and it may have a different recipe compared to chocolate for tablets.

Chocolate is an affordable yet luxury treat with mature markets in North America ad Europe and also developing markets worldwide. The secret behind the universal appeal of chocolate is in the mouthfeel – the “snap” of the first bite, how the chocolate melts and how it coats the inner side of the mouth. In spite of being a consumer experience, mouthfeel is strongly linked to the materials science of chocolate as a composite material. The chocolate’s particle size and rheology are important factors in determining and predicting mouthfeel. This article reveals how rheology and laser diffraction can be employed to characterize the mouthfeel of chocolate.

The mouthfeel, or texture of chocolate is important for the consumer’s perception of the quality of product. The textural aspects of the signature flavor of chocolate brands can be finely controlled by comparing expensive sensory testing with analytical results. The mouthfeel can be characterized by the determination of particle size, flow, rheology and laser diffraction. Rheological techniques can also be used to simulate mastication and thus control or predict the structural changes in the chocolate while it is consumed.

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[4] Beckett, S. (2008) The science of chocolate (2nd edition) RSC Publishing

[5] Chan, F. and De Kee, D. (1994) Yield stress and small amplitude oscillatory flow in transient networks. Industrial & engineering chemistry research, 33(10), p2374-2376

[6] De Graef, V., Depypere, F., Minnaert, M., & Dewettinck, K. (2011). Chocolate yield stress as measured by oscillatory rheology. Food Research International, 44(9), 2660–2665.

[7] Chung, C. et al. (2012) Instrumental mastication assay for texture assessment of semi-solid foods: compile cyclic squeezing flow and shear viscometry. Food research international, 49, p161-169

This information has been sourced, reviewed and adapted from materials provided by Malvern Panalytical.

For more information on this source, please visit Malvern Panalytical.


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