Solidification, of chocolate

In the absence of a full kinetic description of the crystallization process, the assumption that the solidification of chocolate can be modeled using effective heat capacity data as a function of temperature and cooling rate is an acceptable engi-... 

As noted above solidification is critical in manufacture as it determines whether the chocolate will demould successfully. During solidification, the material changes shape. It is not possible to follow the shape of the surface of chocolate using conventional tribological techniques, which involve physical contact between the surface and a stylus of some sort. One technique which can be used to follow the surface morphology of chocolate is to use an infrared laser to measure the sample height. 

The processes of chocolate formation are complex, reflected in the thermal and physical changes in chocolate during processing and cooling. A range of modelling and experimental techniques have been used to study the problem of chocolate solidification. It is possible to model conventional processes using the ideas of... 

Pinschower, K. (2003). Measurement of the contraction of chocolate during solidification. Chemical Engineering. Birmigham, University of Birmingham. PhD. 

The process of tempering - by which the conditions are created for the correct crystal form to be produced - and solidification are thus cmcial to successful chocolate-making. The aim of this chapter is to review work in this area and describe current understanding of the processes and their kinetics. 

In the classical Stefan formulation of phase change problems, solidification occurs at a well defined front which moves though the material (Aziz 2003). This is appropriate for simple materials, but not for chocolate which is a multi-component mixture of triglycerides which displays a spread of melting points. A front is therefore difficult to define. Instead a mushy zone exists instead where solid and liquid co-exist the process is described as continuous solidification (Voiler, Swaminathan and Thomas 1990). 

The optimum horizontal tracking speed was found to be 40 mm/min acquiring 1100 data points, i.e. a horizontal spacing of 36 microns/data point. For measurement, a sample of liquid chocolate which has received a known temperature-time-shear profile is placed within a solidification rig that consists of a mould with known coefficient of expansion, contained in a temperature-controlled holder. 

The removal of unwanted air or gas is important in many food processes and it can be extremely difficult especially in very viscous liquids such as chocolate. Ultrasonically assisted degassing is particularly rapid in aqueous systems and can be used to remove any dissolved gas down to a very low level, thus is of great benefit in situations requiring the rapid and controlled removal of a gas or gases from a system. However ultrasound has also been employed to degas liquids as viscous as molten glass [73] and as dense as molten metals [74] during their solidification process. 

The fat (cocoa butter) of the cocoa beans is important for chocolate production, as it wDl give chocolate its characteristic texture and mouthfeel, depending on the hardness and melting and solidification (crystallization) behavior of the fat (Asep et al. 2008 Beckett 2009 Afoakwa 2010). Fat makes up slightly more than 50% of the mass of dry unfermented cocoa bean cotyledons Forastero beans possess a higher fat content than Criollo beans. The cocoa butter present in the cocoa beans is... 

---