Chocolate can be described as a suspension consisting of non-fat particles (sugar and cocoa solids and, eventually, milk powder particles) dispersed in cocoa butter as a continuous phase. The textural component is critical for consumers that prefer a smooth chocolate to a “gritty” one and smooth chocolate being perceived as a more luxurious product. 
The mouthfeel depends on the composition of the fat phase and the size of the cocoa, milk and sugar particles suspended in the fat. Extensive consumer research by chocolate manufacturers has determined that once a significant number of particles are above 30μm, the mouthfeel begins to deteriorate with consumers rating the chocolate as being of a lower quality.
Particle size is thus a major factor in the texture and flavour of the final product. Typical particle size distribution of chocolate exhibits 2 modes: one mode at approx.5 microns and a second mode at approximatively 30 microns.
Dark chocolate is perceived by consumers as having a smoother and more luxurious texture than Milk and White chocolate because dark chocolate doesn’t have the 30 microns mode.
Chocolate manufacturers need to detect the presence of large particles for better chocolate texture as well as to reduce production cost by optimizing milling process. Particle size parameters such as Dv95, Dv98 or the percentage of particles above 30 μm are typical parameters to differentiate chocolate types and can easily be obtained from laser diffraction particle size analysis.
While solid particles characteristics affect grittiness, the flow properties of the fat phase (cocoa butter, which may be mixed with other fats) control how the chocolate coats the mouth and influences the perception of flavour.
The characteristics and proportions of both the fat and solid phases, together with the changes they undergo during processing, have a large impact on the flow characteristics of chocolate. A broader particle size distribution generally results in a less viscous fluid and consumers are less concerned with a smooth mouthfeel when they are focused on the centre of the chocolate.
A different composition of fats as well as larger solid particles are required for a tablet chocolate respect to a chocolate formulation optimised for the enrobing process. As shown in the graph here below, Dark (red curve ), Milk ( Blue curve ) and White ( Green curve ) exhibits different viscosity profiles.
Dark chocolate having the lowest viscosity and white chocolate highest viscosity.
On top of the viscosity profile rheology is also able to determine Yield stress which is the minimum force required to get the flowing. From below table, despite having different viscosity profiles, Dark and Milk chocolates are having similar yield stress while White chocolate is having a much higher Yield stress. Dark and Milk chocolate will be easier to pump and will fill the moulds more efficiently during manufacturing process than White chocolate that shows a much higher yield stress.
Chocolate is a fat based food product with crystalised cocoa butter from cacao beans as its main constituent: crystal polymorph of cocoa butter can thus be analysed to predict heat resistance, storage stability and texture. In the example below, milk chocolate, high cacao chocolate and creamy chocolate were analysed using Differential Scanning Calorimetry (DSC).
Creamy chocolate melts around room temperature (approx. 25°C), a lower temperature respect to milk and High Cacao chocolate (melting temperature around 33-34°C), explaining the soft structure of creamy chocolate. Milk and High Cacao chocolate will be perceived as harder in the mouth and will then gradually melt to become softer.
Alfatestlab can support you in the analysis of your chocolate products thanks to a complete technological platform dedicated to the food industry. Contact us for more information.
