1. The process of fat bloom formation in pralines and its main causes
Daniel Kalnin
YKI, Institute for Surface Chemistry
Life Sciences and Chemical Industries Section
Stockholm, Sweden
Claudia Delbaere
FTE, Lab of Food Technology and Engineering
Department of Food Safety and Food Quality
Ghent University, Belgium

2. Outline Introduction to fat bloom Chocolate surface structure
Fat bloom mechanisms
Polymorphic transitions
Oil migration
Conclusions

3. Fat bloom
Loss of initial gloss and a grey-whitish haze formed on the chocolate surface
due to the diffraction of light of the fat crystals that are formed on the chocolate surface
This is a significant problem that leads to sensory defects in chocolate

4. Fat bloom ≠ Sugar bloom Caused by condensation (colder  warmer)
Solubilization and recrystallization of sugar at the chocolate surface
Dissolves in water
Bryony J. James, Bronwen G. Smith , “Surface structure and composition of fresh and bloomed chocolate analysed using X-ray photoelectron spectroscopy, cryo-scanning electron microscopy and environmental scanning electron microscopy.” Food Science and Technology ,42 (2009), 929–937.

5. Fat bloom causes Origins of fat bloom → 3 main sources Composition
Incompatible fats
Filled chocolates: center rich in oil content
Processing
Tempering
Post tempering (Cooling)
Storage conditions
Storage temperature
Temperature fluctuations
Time
Lonchampt, P. & Hartel R.W (2004). “Fat bloom in chocolate and compound coatings.” European Journal of Lipid Science and Technology, 106 (4),

6. Fat bloom mechanisms Numerous theories to explain bloom formation
None have covered multiplicity of the bloom problem
The specific mechanisms still remain largely unknown ↓ Fat bloom is a very complex phenomenon
Main theories
Polymorphic transitions (bV – bVI)
Eutectic effects (Phase separation)
Migration of oil
Recrystallization

7. Fat bloom crystals - Scanning Electron Microscopy -
Fat bloom on well tempered chocolate
Fat bloom on untempered chocolate
5 μm
5 μm
Bryony J. James, Bronwen G. Smith , “Surface structure and composition of fresh and bloomed chocolate analysed using X-ray photoelectron spectroscopy, cryo-scanning electron microscopy and environmental scanning electron microscopy.” Food Science and Technology ,42 (2009), 929–937.

8. In order to understand what happens when fat bloom forms on chocolate
Identify and follow development at the very surface and understand what is going on before fat bloom occurs

9. Surface roughness - Profilometry -
Measure at the same spot as a function of time
Qualitatively and quantitatively

10. Chocolate surface structure - Scanning Electron Microscopy -
Fresh chocolate surface
Fat bloom crystals on the surface

11. Chocolate surface structure - Scanning Electron Microscopy -
Clusters of fat bloom crystals
Fat bloom crystals covering the surface

12. Chocolate surface structure - Scanning Electron Microscopy -
Pores
Protrusions

13. Chocolate surface structure - Atomic Force Microscopy (AFM) imaging of chocolate surface -
Sonwai, S. and D. Rousseau (2008). "Fat crystal growth and microstructural evolution in industrial milk chocolate."
Crystal Growth & Design 8(9):

14. Distribution of different components at the surface
- Confocal Raman Microscopy -
Fat Sugar Air

15. Pores in chocolate
Rousseau, D. and P. Smith (2008). "Microstructure of fat bloom development in plain and filled chocolate confections."
Soft Matter 4(8):

16. Fat bloom mechanisms Main theories Fat bloom
Polymorphic transitions (bV – bVI)
Eutectic effects (Phase separation )
Migration of oil
Recrystallization
Fat bloom
Plain chocolate: cocoa butter crystal polymorphism (bV – bVI)
Composed chocolate products: migration of ‘liquid’ foreign lipids (e.g. from the filling, nut, biscuit) into the chocolate

17. Polymorphic transitions
Liquid α βV
βVI γ ’
direct crystallization (during cooling)
melting
recrystallization
Bloomed chocolate
Well tempered chocolate
Van Malssen, K., Van Langevelde, A., Peschar, R. & Schenk, H. (1999). Phase behavior and extended phase scheme of static cocoa butter investigated with real-time x-ray powder diffraction. Journal of the American Oil Chemists Society, 76 (6),

18. Polymorphic transitions
Liquid α βV
βVI γ ’
Crystal problem
Fat bloom → bVI
Most stable crystals!
At the outside as well as inside
Van Malssen, K., Van Langevelde, A., Peschar, R. & Schenk, H. (1999). Phase behavior and extended phase scheme of static cocoa butter investigated with real-time x-ray powder diffraction. Journal of the American Oil Chemists Society, 76 (6),

19. Polymorphic transitions
Several causes
Composition
Plain chocolate: cocoa butter crystal polymorphism (bV → bVI)
Migration: foreign fat induces bV- bVI transition (See ‘Migration fat bloom’)
Processing
Incorrect tempering
Undertempering
Insufficient nuclei to ensure good crystallization upon cooling
Generation of unstable polymorphs (b’)
Recrystallization (b’→ bV or bVI) during early storage
Overtempering
Crystal concentration is too high
Poor crystallization in the mold, reduced contraction
Gray dull and no bright surface

20. Polymorphic transitions
Several causes
Processing
Cooling rate
Cooling too fast
Generation of unstable polymorphs (b’)
Recrystallization (b’→ bV or bVI) during early storage
Storage
Polymorphic transition (bV → bVI) is inevitable !

21. Eutectic effects
Phase separation between two physically incompatible fats
Eutectic mixture: melting point lower than the melting points of either of the two pure fats
Phase separation of the two incompatible fats
Recrystallization of the individual fats
Polymorphic transitions
Hartel, R. (1996). Applications of milk-fat fractions in confectionery products. Journal of the American Oil Chemists Society, 73,

22. Image: courtesy of FTE (Ghent University)
Migration fat bloom
Image: courtesy of FTE (Ghent University)

23. Image: courtesy of FTE (Ghent University)
Migration fat bloom
Image: courtesy of FTE (Ghent University)

24. Image: courtesy of FTE (Ghent University)
Migration fat bloom
Image: courtesy of FTE (Ghent University)

25. Migration fat bloom Plain dark chocolate Cocoa powder particles Sugar
Matrix of cocoa butter

26. Migration fat bloom Filled chocolate products Fat based fillings ↓
Chocolate surface
Fat based fillings ↓
Oil migration
Fat bloom
Chocolate shell
Interphase
Filling

27. Migration fat bloom
Liquid oil migrates into the shell and dissolves cocoa butter TAGs, which then are carried to the surface of the chocolate.
Image from: Galdamez, J. R., K. Szlachetka, et al. (2009). "Oil migration in chocolate: A case of non-Fickian diffusion." Journal of Food Engineering 92(3):

28. Migration fat bloom Filled chocolate products
Less research compared to plain chocolate bloom
In contrast with current higher industrial relevance !
Migration of ‘liquid’ foreign lipids (e.g. from the filling, nut, biscuit) into the chocolate
Driving force = difference in TAG concentration
Smith, K., Cain, F.& Talbot, G. (2007). Effect of nut oil migration on polymorphic transformation in a model system. Food Chemistry, 102 (6),

29. Migration fat bloom Filled chocolate products
Rate of migration is rapid at the start and slows down with time
Ziegleder, G., Moser, C. & GeierGrequska, J. (1996). Kinetics of fat migration within chocolate products .2. Influence of storage temperature, diffusion coefficient, solid fat content. Fett-Lipid, 98 (7-8),

30. Composition analysis of fat bloom in filled chocolate products have shown that it contains about 15% of Triolein, which is a proof for the diffusion of vegetable oils from the centre through the coating into the bloomed surface.
Ziegleder, G. (1997). "Fat migration and bloom." The manufacturing confectioner.

31. Migration fat bloom Fresh chocolate POP + POS + SOS
3 main triglycerides
POP + POS + SOS
POS
SOS
POP

32. Migration fat bloom Bloomed chocolate chocolate triglycerides
+ filling specific triglycerides, e.g., OOO
OOO
LOO

33. Migration fat bloom Filled chocolate products
The liquid fat from the filling will mix with the cocoa butter present in the chocolate
Decrease of solid fat content in chocolate shell due to
Dissolution of the cocoa butter crystals in the liquid fat
The formation of a eutectic phase
Leads to migration of liquid cocoa butter to the surface
Recrystallization at the surface
Formation of fat bloom
→ Migration: foreign fat induces bV- bVI transition
Importance of microstructure
Migration does not always lead to fat bloom
Structure density decisive for crystal development?

34. Migration fat bloom Diffusion
Molecular or Fickian diffusion is widely used as a general model for mass transfer
Simplified solutions to Fick’s second law of diffusion are used to model fat migration
Assumption: diffusion of oil through chocolate occurs only in the liquid fat phase
New predictive model takes not only the molecular diffusivity but also the internal microstructure of the chocolate into account
 = void fraction
 = tortuosity
Ziegler, G., Shetty, A. & Anantheswaran, R. (2004). Nut oil migration through chocolate. The Manufacturing Confectioner, September,
Galdámez, J., Szlachetka, K., Duda, J. & Ziegler, G. (2009). Oil migration in chocolate: A case of non-Fickian diffusion. Journal of Food Engineering, 92,

35. Migration fat bloom Capillary forces Diffusion or capillary flow?
Capillary flow in pores and channels
Related to the porosity of the chocolate
Diffusion or capillary flow?
Some authors support the hypothesis of diffusion, whereas others find evidence for the hypothesis of capillary flow

36. Migration fat bloom research
HPLC analysis Triglyceride composition
X-ray diffraction Polymorphic forms
DSC measurements Melting behavior
NMR measurements Solid fat content
Texture analyzer Hardness
Automated image analysis Fat bloom evaluation
Microscopy techniques
SEM Surface microstructure
CLSM Microstructure
Sensory research Visual fat bloom, hardness, melting behavior … C 10 F 1

37. Conclusions Origins of fat bloom → 3 main sources Composition
Incompatible fats
Filled chocolates: center rich in oil content
Processing
Tempering
Cooling
Storage conditions
Storage temperature
Temperature fluctuations
← Eutectic effects + re-crystallization
← Oil migration
+ dissolution re-crystallization polymorphic transition
← Polymorphic transition
← Oil migration polymorphic transition