Melting of Chocolate - METTLER TOLEDO

Melting of Chocolate

Sample

Milk chocolate, Lindt chocolate bar

 

Conditions

Measuring cell: DSC30

Pan: Aluminum standard 40 µl, hermetically sealed

Sample preparation: Sample was cut from a bar with a sharp knife and transferred to an aluminum pan without warming (heat from hands!). Sample weight 17.33 mg

1) Cooling from room temperature to -30 °C in approx. 5 min

2) Cooling from 15 °C to -30 °C in approx. 4 min

Interpretation

In this experiment, commercial milk chocolate is used without any further preparation to demonstrate how the crystal modifications vary as a function of the crystallization conditions. The curve labeled ‘original’ shows the melting behavior of a sample of commercial milk chocolate stored at 5 °C after purchase. Between 10 °C and 20 °C an exothermic transition peak can be clearly recognized (rearrangement to the stable form). Above 30 °C (oral temperature) the melting range of the `-modification begins. This modification was achieved technically by gentle annealing. Because of the high heating rate (which was selected to obtain larger peaks), the individual melt fractions are not further resolved.

After faster cooling of the same melt to -30 °C at 20 K/min, the curve labeled ‘after rapid crystallization’ shows new melting characteristics. Only the unstable form is present. The total heat of fusion of the same sample has decreased from 541 mJ (original milk chocolate) to 360 mJ. The rapidly crystallized chocolate no longer satisfies the sensory requirements.

The same sample was now cooled from the melt to 15 °C at a rate of 1 K/min, held isothermicly for 15 minutes and then cooled to -30°C. These annealing conditions are intended to simulate a ‘slow and careful’ crystallization. The melting behavior of this sample is shown by the curve labeled ‘after slow cooling’. The α-form already starts to melt at 5 °C. There is virtually no further rearrangement (as a result of the high heating rate). Only about half the original β-modification is now present and melts above 30 °C.

 

Evaluation

Peak integration gives the results needed to estimate the relative stability of the fat modification:

Conclusions

The raw material quality, the process parameters and the composition of the chocolate have an influence on the shape of the DSC melting curve.

 

Melting of Chocolate | Thermal Analysis Application No. HB 1014 | Application published in METTLER TOLEDO TA Application Handbook Food