on behalf of u cocoa butter crystallisation kevin w. smith & kees van malssen unilever r&d...
TRANSCRIPT
on behalf of
u
Cocoa Butter CrystallisationCocoa Butter CrystallisationKevin W. Smith
&
Kees van Malssen
Unilever R&D Colworth
October 2002 2
OutlineOutline
Introduction Cocoa Butter and Chocolate
Cocoa Butter Crystallisation Phase Transformations Phase Behaviour and Crystallites
Conclusion
October 2002 3
Cocoa Butter & ChocolateCocoa Butter & Chocolate
Crucial role in chocolate characteristics Gloss Snap Texture Cool melting in mouth Shelf-life
Important to crystallise cocoa butter correctly
1010mm
October 2002 4
Fat PolymorphismFat Polymorphism
Crystal Structure few triacylglycerols known main components of cocoa butter not known
• POP, POSt and StOSt
• many proposed structures natural fats are complex mixtures
• observed crystal structure is an average
• new polymorphs may occur
October 2002 5
Cocoa Butter PolymorphismCocoa Butter Polymorphism
Wille and Lutton (JAOCS, 1966)
StabilityMelting
Point (°C)Basic
PolymorphI least stable 17 /sub-
II meta-stable 23
III meta-stable 25 '2IV meta-stable 28 '1V stable 33
2
VI most stable 36 1
October 2002 6
Cocoa Butter PolymorphismCocoa Butter Polymorphism
Current understanding
StabilityMelting
Point (°C)Basic
Polymorphunstable 0 /sub-
unstable 17
meta-stable 21-28 '
stable 31.5 V
most stable 33.5 VI
October 2002 7
Static Isothermal CrystallisationStatic Isothermal Crystallisation
/sub-
liquid
-20
-10
0
10
20
30
40
Tc
(°C
)
1 0s 2 0s3 0s 2 m 3 m4 m 10 m 20 m30 m 2 h3 h 6 h 12 h 18 h 2 d3 d4 d 2 w3 w
1 min 1 hour 1 day 1 week
Time (logarithmic)
October 2002 8
' Phase Range Diffraction' Phase Range Diffraction
'25.0
'22.5
'20.0
'17.5
'15.0
'12.5
'10.0
'5.0
6.0 5.0 4.5 4.0 3.5d(Å)
14 16 18 20 22 24 26 282q(° )
Intensity
October 2002 9
' Melting Dependent on ' Melting Dependent on Crystallisation TemperatureCrystallisation Temperature
0
20
40
60
80
100
20 22 24 26 28 30
Temperature (°C)
Pea
k I
nte
nsi
ty (
% o
f m
ax)
20°C15°C10°C5°C
October 2002 10
Cocoa Butter Phase SchemeCocoa Butter Phase Scheme
Melt
VI
V
or sub-
'
Solvent
October 2002 11
Assignment of PolymorphsAssignment of PolymorphsApprox.
MPt. (°C)Wille &Lutton
TraditionalCurrent
Data0 / sub-
17 I sub-
23 II '*
25 III ' '*
28 IV ' '*
33 V
36 VI
* and many more
October 2002 12
Phase Behaviour and CrystallitesPhase Behaviour and Crystallites
B (%)
A BT
empe
ratu
re
100
LiquidL+S
Solid
0 20 40 60 80
23
4
6 5
1
October 2002 13
Crystallites CompositionCrystallites Composition
October 2002 14
Crystallites - Small CrystalsCrystallites - Small Crystals
October 2002 15
Crystallites - Different SizesCrystallites - Different Sizes
October 2002 16
Crystallites - Different CompositionCrystallites - Different Composition
October 2002 17
Complex Phase BehaviourComplex Phase Behaviour
B (%)
A BT
empe
ratu
re L
L+SB
L+SA
SBSA
SA + SB
1000 20 40 60 80
October 2002 18
Cocoa Butter CrystallisationCocoa Butter Crystallisation
Composition dependent Solidification in two stages
high melting fraction first• molten cocoa butter cooled to 30°C will develop a
cloudiness but will not crystallise over 12 weeks bulk second
Increasing first stage may not accelerate second stage
• trisaturated triacylglycerols are not good accelerators
October 2002 19
Memory Effect & Crystallisation Memory Effect & Crystallisation
Memory of crystal form remains in liquid cocoa butter up to 7°C above melting point
Subsequent crystallisation occurs into stable form a type of seeding can be used to 'temper' chocolate
Temperature for loss of memory effect is independent of cocoa butter composition
October 2002 20
SummarySummary
Assignment of polymorphs to melting points has been mistaken
Solidification temperature determines phase, more than cooling rate
Phases develop faster through phase transitions than through nucleation
phases do not crystallise from the melt (excluding seeding effects)
October 2002 21
AcknowledgementsAcknowledgements
Unilever R&D Colworth: Dr. Kees van Malssen Loders Croklaan University of Amsterdam: A van Langevelde, R
Peschar, H Schenk Netherlands Foundation for Chemical Research
(NWO/CW) and Dutch Technology foundation (STW)
October 2002 22
October 2002 23
AdditionalAdditional
Wille and Lutton
I sub mp 17
II mp 23 III ' mp 25 IV ' mp 28 V mp 33 VI mp 36
Van Malssen / sub mp 0 mp 17 ' x mp 23* ' y mp 25* ' z mp 28* mp
31 mp
33• * and many more possible!