Predicting chocolate stability

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                                                                      RHEOLASER Crystal

 

 rheolasercrystal


Application

Food


 Introduction

Crystallization is one of the most critical steps for chocolate makers.

Chocolate can crystallize in six forms but only two of them are stable during several months and only one of them brings the glossy aspect, the snap and delivers the sophisticated aromas of chocolate (β(V)). The other stable form (β(VI)) is almost impossible to obtain with melted chocolate.

The unstable forms evolve during the storage and initiate the fat bloom (chocolates that appears white on the surface). That is why, it is important for chocolate makers to insure a crystallization to the β(V) forms thanks to a controlled process.

It is now possible, thanks to the RHEOLASER Crystal, to control, easily and quickly, the major crystalline form of a chocolate directly at the end of the process. This control allows monitoring of the entire process (tempering and cooling) in order to avoid fat bloom.


 Objective

Analyse chocloate to determine the major crystalline form of a chocolate, at the end of the process.


Device

Rheolaser Crystal


 

Reminder on the technique

RHEOLASER Crystal uses the DWS principle.Lightgraph1 is scattered by the particles, creating an interference pattern (Speckle Image). The variation of this image is related to the motion of the particles. By a mathematical analysis of this variation, decorrelation functions can be calculated and then processed, to obtain a characteristic time τ as a function of time or temperature.
Values of 1/τ or Micro-Dynamics (Hz), are then plotted against time or temperature, resulting in characteristic peaks when the product shows a microstructural evolution, such as a phase transition or any other physical event. The signal can then be integrated for an easier visualisation, obtaining the so-called Micro-Dynamics Evolution (%).

 

 Method

In experiment 1, we present two types of chocolates, with the exact same composition:
- A correctly tempered chocolate, with a temperindex of 5.0 (*)
- An under-tempered chocolate, composed of unstable forms with a temperindex of 1.5(*)
Chocolates where analyzed after the same cooling protocol (10 minutes at 12°C + 1 hour at 18°C).

In experiment 2, we used two correctly tempered chocolates with the exact same composition, but different cooling conditions:
- A chocolate cooled at 12°C for 6 minutes, then 1h at 18°C.
- The other was cooled at 12°C for 15 minutes, then 1h at 18°C.
Analyses were performed with a RHEOLASER Crystal: samples were heated from 16°C to 35°C at a speed of 3°C per minute.

 * The temperindex is a tool used to control chocolate tempering. It’s based on increase of temperature during crystallization. A well-tempered chocolate has a temperindex of 5.0 (optimal crystal percentage), an under-tempered chocolate shows a temperindex below 4.0 (not many crystals after tempering).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Experimental results
1) Impact of tempering
The under-tempered chocolate shows a lower transition temperature
than the well-tempered chocolate.
Micro-Dynamics Evolution (μDE) shows a transition temperature of 26°C for under-tempered and 31°C for well-tempered chocolate
(figure 1).
These temperatures correspond to the melting temperature of form β’(IV) (an unstable form) and of form β(V) (the best form).
We can certify that the under-tempered chocolate is mainly
composed of cocoa butter under the β’(IV) form while the welltempered chocolate is mainly composed of β(V) form.
Under tempered chocolate will have a high probability to evolve in a stable form (generally, the β(VI) form) and to initiate blooming. After some weeks some weeks, the under-tempererd chocolate                    Figure 1 Micro-Dynamics Evolution as a function
presented visually a greyish aspect on the top( fat bloom)                                 of temperature for a tempered chocolate
while the other one was still shiny and good looking                              (green) and for an under-tempered chocolate (red).

    2) Impact of cooling 

Tempering is an important step in the process of chocolate, but a good tempering doesn't guarantee the stability of chocolate. In figure 2, both chocolates are well tempered (temper index of 5.0) but cooling conditions differ. The chocolate cooled during 6 minutes shows a lower transition temperature than chocolate cooled during 15 minutes. That means it was composed, in large part, of unstable crystals. In contrast the chocolate with 15 minutes of cooling had a part of unstable crystals (increase of signal before 30°C) but was principally composed of stable crystals (increase after 30°C).
After 3 months, chocolate with 6 minutes of cooling shows bloom formation, not the other one.
The temperindex doesn’t guarantee a quality of crystals in chocolate. RHEOLASER Crystal, can easily, discriminate a stable or instable chocolate at the end of the production line, depending on any parameters of the process.

 

 graph3

Figure 2 Micro-Dynamics Evolution in function of temperature for two tempered
chocolate. A chocolate was cooled during 6 minutes (red) and the other during 15
minutes (blue) at 12°C.

Rheolaser Crystal offers:

PREDICITIVE - anticipate long-term phenomena

ACCURATE - nano-scale sensitivity, large sample, direct sampling with no denaturation

EASY - 1-click set-up and data treatment

 

Summary
The RHEOLASER Crystal makes it posable to determine the major crystalline form of a chocolate, at the end of the process. 

Just like in DSC (Differential Scanning Calorimetry), the determination of crystals form is based on the difference of melting temperatures, but with the Rheolaser Crystal is easier to set up through an easy to use sampling system which limits the risk of modification of the crystalline form and enable us to work with multi-component systems.

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