Determination of Particle Size Distribution of Chocolate

The size of particles present within chocolate products and chocolate itself have a major impact on the feel of the chocolate product within the consumer’s mouth. For example, a small particle size produces a very ‘smooth’ feeling.

In order to meet desired standards of quality and particularly smoothness, it is necessary to carefully test final products but, perhaps even more importantly, it is imperative to monitor the production process itself.

Analysis of Three Different Chocolate Types

Within the example presented here, particle size distributions of various types of high quality chocolate – all from the same manufacturer – were measured using a FRITSCH ANALYSETTE 22. Before measuring, the chocolate samples were pre-dispersed within an organic solvent.

The image below shows:

  • The cumulative curve distribution Q3(x) (top)
  • The histogram dQ3(x) (bottom)

As can be seen, the volume share per particle size interval is visible for all the different types of chocolate and in this case, the chocolate that has a cocoa share over 99% will result in an incredibly intense taste with a mouth feel that is almost ‘sticky’.

Visible Differences

Clear and significant differences can be seen: for example, the chocolate that has a higher proportion of cocoa has a finer particle size distribution than something like milk chocolate, leading to a smooth taste and even a sticky sensation that can lead to the taste being very intense.

Where chocolate has a higher sugar content – for example in milk chocolate – this will tend to favor a particle size distribution that is shifted towards bigger particles. In the density distribution here, there is a dominant peak at around 20 µm, but over 95% of the sample is still shown to have particles that are smaller than 30 µm.

The higher upper limit of particle sizes that is caused by the presence of sugar crystals is less important for the feel of the chocolate within the mouth, because these quickly dissolve as the chocolate is eaten.

Analysis of Identical Samples

Reproducibility is a key consideration when measuring particle size distributions. The image below illustrates the cumulative curve distributions Q3(x) of 5 consecutive measurements of a sample that was taken from the production process of milk chocolate as a means of controlling the conching process.

Here, around 5 g of chocolate was added to a beaker before being pre-dispersed in an organic solvent via an external ultrasonic bath. Once this was done, ten measurements were taken by adding a small amount of sample material to the ANALYSETTE 22’s small volume wet dispersion unit.

The dispersion unit was flushed, and the system refilled with solvent following each measurement.

Conclusion

The image above shows a tiny variation in particle size distribution between measurements, but this was primarily due to the sampling process.  Here, when taking a small amount of material from the beaker glass the actual distribution will vary slightly, though this can be eliminated by averaging over several measurements.

Most crucially, a suitable solvent must be used when measuring chocolate samples. If a suitable solvent is not used, the chocolate samples’ high fat content will quickly contaminate the measurement cell glass.

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

For more information on this source, please visit FRITSCH GMBH - Milling and Sizing.

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