Polymorphism of chocolate
S. Almeida and N. Allemann
Ecole d’Ingénieurs et d’Architectes de Fribourg
Bd de Pérolles 80 – CP 32
CH – 1705 Fribourg
[email protected], [email protected]
The purpose of this project was to study the different polymorphic forms of chocolate using
calorimetric methods. The main component of chocolate is cocoa butter. Cocoa butter is
composed of triglycerides which are in motion in the liquid state. When these triglycerides
solidify, they will form structures. If these structures are regular, we can speak of
crystallization. The characteristic of cocoa butter is that it can crystallize in different
structures: this is called polymorphism. There are six polymorphic forms of cocoa butter. The
desired form, calls form V, has a melting point between 32 and 34°C. This form has all the
benefits of a good chocolate: the chocolate is smooth, shiny, easy to break, crunchy.
Chocolate with the form V melt only in the mouth and has a pleasant taste and texture. Form
V is achieved by tempering chocolate. This is a key step in the preparation of chocolate.
Tempering allows to obtain the most stable crystalline form by following specific
temperatures sequences. To achieve the goal of this project, several products were analyzed;
cocoa butter, couverture chocolate (which must contain at least 32% cocoa butter) and
homemade chocolate to try to observe other polymorphic forms.
A DSC (Differential Scanning Calorimetry) was used to determine the cocoa butter melting
point. The DSC measure the heat transfer between a system and the environment during a
process like fusion. During this project, a DSC with a heat flow mode was used. The
apparatus have one oven which contains the reference and the sample. The difference of the
heat flow between oven / sample and oven / reference is measured.
An Easy-Max, developed by Mettler Toledo, was also used to determine the cocoa butter
melting point. The Easy-Max is a calorimetric reactor and it is very commonly used for a
scale-up development. It is possible to work in three modes: isoperhibolic, quasi-adiabatic or
with temperature ramp. In this project, the Easy-Max presents an advantage because it is
possible to work in a wide temperature range (-40 to 180°C).
The results obtained with the DSC are inconclusive. Cocoa butter and homemade chocolate
were analyzed. Our DSC does not have a cryostat to cool the device. Therefore, the
temperature of the DSC does not drop below 25°C and the melting temperatures found are not
correct. Cocoa butter and homemade chocolate are already soft when introduced into the DSC
because it has a relatively low melting point. The tests were then made with Easy-Max. The
results are not as expected. Chocolates made without tempering method (which should
therefore not be in the form V) and cocoa butter and couverture chocolate (which are in the
form V) give the same melting temperature when no temperature ramp is applied. When a
temperature gradient is applied, results are difficult to interpret because they present more
melting peaks (also for the cocoa butter for example). The Easy-Max is not a suitable
instrument for this kind of calorimetric analysis because on the interpretation. The analysis
could be performed properly if the DSC could be cooled.
Finally, organoleptic tests were performed on different homemade chocolates and show that it
is very important to temper chocolate for taste, texture and optimum brightness.
Polymorphism of chocolate
Sofia Almeida, Noémie Allemann, Pierre Brodard
University of Applied Sciences of Western Switzerland
CH‐1705 Fribourg, SWITZERLAND
DSC results
[email protected]
[email protected]
INTRODUCTION
The chocolate is a product which is appreciated and consumed by a lot of
people. The main component of chocolate is cocoa butter. The chocolate
must have a good taste, texture and an optimal shine. For this, it is
important to follow specific temperature ramps; it’s called tempering.
With tempering, the cocoa butter can cristallize in the form V which is the
most stable form.
In this project, two devices were used : DSC and Easy‐Max.
The DSC presents inconclusives results. In fact, it is impossible to cool the DSC
apparatus bellow 25°C, so the chocolate and the cocoa butter are already soft
before the analysis.
Goal of the project
Easy‐Max results
Chocolat 1/3 2/3 sans rampe de température
120
1
100
80
80
60
60
40
20
Tr
0
Tj
‐20
40
‐60
‐80
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
‐80
18.00
0.00
3
Source : 1
Advantages of the form V:
•
•
•
•
•
•
Smooth
Shiny
Easy to unmold
Crisp
Only melt in the mouth
Good texture in the mouth and good taste
Tempering curve
6.00
8.00
10.00
12.00
14.00
16.00
18.00
4
Beurre de cacao 0.5 K/min
50
40
60
40
20
Tr
0
Tj
‐20
Tr‐Tj
‐40
Température [°C]
17
23
25
27
34
36
4.00
Temps [min]
Copeaux sans recette sans rampe de température
Sub‐α
α
β'
β'
β
β'
2.00
Temps [min]
Température [°C]
I
II
III
IV
V
VI
Tj
‐60
80
Melting point [°C]
Tr
0
‐40
100
Forms
Tr‐Tj
20
‐20
Tr‐Tj
‐40
Polymorphics forms
2
Beurre de cacao (sans rampe de température)
120
100
Température [°C]
Implement a procedure to manufacture a chocolate with the form V
Analyse the pure cocoa butter and the chocolate by DSC
Make chocolate with different tempering methods
Make chocolate without tempering method to observe other cristalline forms
Analyse the pure cocoa butter and the chocolate by Easy‐Max
Do organoleptics tests
Température [°C]
• Characterize the different polymorphic forms of the cocoa butter by a calorimetric method
•
•
•
•
•
•
Pure cocoa butter
Mp: 31.4°C
Homemade chocolate
Mp : 31.1°C
30
Tr
20
Tj
10
Tr‐Tj
0
‐60
‐80
‐10
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
20.00
0.00
10.00
20.00
Temps [min]
1
Mp : 31.7°C
30.00
40.00
50.00
60.00
70.00
80.00
Temps [min]
2
Mp : 32.1°C
3
Mp : 32.6°C
4
31.1°C
The Easy‐Max presents inconclusives results. Chocolates made without
tempering method (which should therefore not be in the form V) and cocoa
butter and homemade chocolate (which are in the form V) give the same
melting temperature when fast temperature ramp is applied. When a
temperature gradient is applied, results are difficult to interpret because they
present more melting peaks.
Organoleptics tests
Chocolate without
tempering method
Chocolate with
tempering method
The pictures show that it is important to temper the chocolate to have all the advantages previously cited.
CONCLUSIONS
Source : 2
1. Debaste, F. La cristallisation du chocolat: entre science et savoir‐faire; Ecole Polytechnique de Bruxelles: Bruxelles, 2014; pp 1‐49
2. Vincent Boué, H. D., Didier Stéphan, Encyclopédie des desserts. Flammarion: 2012
• The DSC must have a cryostat for chocolate analysis
• Easy‐Max is not a suitable instrument for this kind of
calorimetric analysis
• Tempering is very important to have a good chocolate