Effects of shear on crystal forms and crystal growth rate in cocoa butter

Foo, Eric Suan Han (2004). Effects of shear on crystal forms and crystal growth rate in cocoa butter B.Sc Thesis, School of Engineering, The University of Queensland.

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Author Foo, Eric Suan Han
Thesis Title Effects of shear on crystal forms and crystal growth rate in cocoa butter
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2004
Thesis type B.Sc Thesis
Supervisor Professor Ted White
Professor Bill Whiten
Total pages 57
Language eng
Subjects 0904 Chemical Engineering
Formatted abstract

Cocoa butter is an edible vegetable fat extracted from cocoa beans. It is most commonly used to manufacture various types of chocolate confectionery, pharmaceutical ointments and toiletries. It is particularly useful in manufacturing chocolate because it remains brittle at room temperature and lower and melts at just below body temperature. However, this melting characteristic will only be achieved if the cocoa butter crystals are in the desired form of crystals (polymorphs).  

Polymorphism means that a substance can solidify into many different crystalline forms. Currently, it is believed that six forms of crystals exist in cocoa butter (I, II, III, IV, V, VI). Form V crystal is understood to be the most stable and is the desired crystals form as it has the melting characteristic stated above. It has been a major interest among chocolate manufacturers to derive a technology for good chocolate production by ensuring that only this stable form of cocoa butter crystals exist in the final product. However, due to the limited understanding of polymorphism in cocoa butter, full transformation to the desired stable crystal form is rarely achieved. Currently, tempering (temperature and shear programming) is the “best” method chocolate manufacturers have to produce good quality chocolate.  

Tempering requires careful temperature and time control and involves putting cocoa butter under shear. It is believed that shearing is a useful mechanism in nucleating form V crystals. It is also believed that shearing increases the growth rate of crystals. Currently, there is limited research and experiments done on the effect of shear on cocoa butter. In this thesis, cocoa butter samples are prepared under different shear speed and shear time to investigate the effect of shearing on the crystal forms and crystal growth in cocoa butter.  

The results conclude that shearing does produce form V crystals, but too much shear has a detrimental effect on crystal phase produced. It is also suspected that initial shearing will produce form V crystals but if cocoa butter is over-sheared, the highly stable form V crystals transform back into lower stability crystals. The results also show that shearing speed has little impact on crystal forms nucleated but shear time does has a major impact.

Keyword Cocoa butter
Crystal forms
Crystal growth
Shear effects
Additional Notes * Chemical Engineering undergraduate theses. 2004

Document type: Thesis
Collection: UQ Theses (non-RHD) - UQ staff and students only
Citation counts: Google Scholar Search Google Scholar
Created: Tue, 15 Oct 2013, 14:45:55 EST by Mr Yun Xiao on behalf of Scholarly Communication and Digitisation Service