Measuring the Particle Size Distribution of Chocolate

The particles size of chocolate and chocolate products strongly impacts the mouth feel of the chocolate itself. For instance, if the size of the particles is relatively small, the sensation in the mouth is smoother. Therefore, to achieve the desired level of quality the final product as well as the production process need to be carefully tested and monitored.

Analysis of Different Chocolate Types

The particle size distributions of different types of high-quality chocolate from the same producer were determined using a FRITSCH ANALYSETTE 22. Before the measurement, chocolate samples were pre-dispersed in an organic solvent. Figure 1 shows both the cumulative curve (upper portion of the graph) and the density distribution (lower portion of the graph) of the different chocolate samples.

Figure 1. Particle size distribution for three different types of chocolate.

The very fine distribution of the 99% cacao chocolate results in a very intensive taste and an almost “sticky” mouth sensation. Significant differences can be noticed:

• The chocolate with a large cacao fraction has a finer particle size distribution (PSD) than, for instance, milk chocolate. This results in a very smooth and even sticky sensation.
• Higher sugar content as in milk chocolate results in a PSD shifted towards larger particles.
• In the density distribution, a 20-µm peak is dominant, but still more than 95% of the particles have dimensions smaller than 30  µm. The larger upper limit of sugar crystals is less critical for the mouth sensation and the taste as they quickly dissolve in the mouth.

Analysis of Identical Samples

During measurement of the particle size distribution, reproducibility is of major interest. Figure 2 shows the sum curve of five consecutive measurements of a sample taken from the production process of milk chocolate to control the conching process. About 5 g of chocolate were added to a glass beaker and were pre-dispersed in an organic solvent with the help of an external ultrasonic bath. From this beaker, a small amount of the sample material was added to the small volume dispersion unit of the ANALYSETTE 22 for each measurement. After the analysis, the sample was discarded and the system was refilled with solvent for the next measurement.

Figure 2. Five consecutive measurements of chocolate samples from the same production batch, for each of the five measurements a new aliquot was used.

The tiny variation of the particle size distribution from measurement to measurement as seen in Figure 2 is mainly due to the sampling process. Taking a small amount of material from the beaker is expected to cause a slight difference in the actual size distribution. Averaging over several measurements helps eliminating this effect. It is very important that a suitable solvent is used to measure the chocolate samples, since the high content of fat in chocolate could quickly result in the contamination of the measurement cell windows.

This information has been sourced, reviewed and adapted from materials provided by FRITSCH GMBH - Milling and Sizing.

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