A box of chocolates offers a full sensory experience. The look, the smell, the taste – all contribute to the appeal of the brand (and dictates how many you will eat in one sitting!).
But there is another factor involved in the total chocolate sensory experience; an important property for the success of a chocolate is mouth feeling. Stephen Campbell, author of “The Mouthfeel of Chocolate & The Cacao Tree,” explained in a Food Editorial.Co online food guide article that the chemical and physical interaction of a food and the mouth is called ‘mouthfeel,’ which is used to evaluate the perception of the palate from the first bite through chewing and swallowing.
In the article he explains how there are several things that are considered modifiers when testing the mouthfeel of chocolate: chewiness, graininess, heaviness, moisture absorption, smoothness, uniformity, and viscosity. He goes on to say that “Many of these modifiers are not desirable in tasting chocolate, as chocolate is supposed to be smooth and creamy to the palate,”… and that “poor quality chocolates are rough or grainy.”
To better understand how to achieve the desired mouth feeling and other physical properties, more detailed measurements on the basic materials, for example the fat contained in the chocolate, as well as on the final product are needed. Since the International Office of Cocoa, Chocolate and Sugar Confectionery (OICCC) introduced rheological tests to control the quality of chocolates, measuring the viscosity and the yield stress are a must in the quality assurance of the chocolate industry. Mouth feeling, however, cannot be predicted using viscosity or yield stress data, so we tested several fat and chocolate samples using rheology methods.
We used a highly flexible Modular Advanced Rheometer System (MARS), to look at the crystallation behavior of the fat. When talking about the recipes for chocolate, the fats used and their complex crystallization behavior are among the most important factors to look at for mouth feeling. However, the different crystalline phases and their individual crystallization points are often difficult to distinguish, so we used a high performance rheometer with a state of the art microscope. The rheometer facilitates measurements in the temperature range from – 5 up to 120°C (although other rheometers are available with a 300°C range if needed). Images with a frame rate up to 15 per seconds were taken with objectives of 5, 10, 20 and 50 times.
With an oscillating rheometer, different crystallization points were observed separately. Using an instrument that combines rheometry and microscopy (RheoScope) the melting or crystallization process was followed with rheological methods while at the same time the growth of the crystals and their individual shapes were observed. Structural changes like the formation of crystals were observed simultaneously while recording the rheological properties thus leading to a deeper understanding why the rheological properties change in the observed way.
In addition, the hardness of the chocolate and the force needed to break it also have to fulfill certain consumer expectations. With a specially designed bending tool, using the normal force sensor and lift drive of a standard rheometer, the compliance of the chocolate as well as the force needed to break the chocolate could be determined accurately.
To see the resulting charts and microscopic images of the homogenous molten fat before and after crystallization, as well as the spectra of measured data for a breaking test on dark and a milk chocolate, see the application note: “Rheology of chocolate from a different point of view.”