Molten chocolate

While free fat remains a controversial concept in liquid dairy products, it undoubtedly has an important role in whole milk powder (WMP) for certain applications (e.g., chocolate manufacture) high-free fat WMP is favored. Keogh et al, (2003) reported that the particle size in chocolate mixes after refining and the viscosity of the molten chocolate decreases as the free fat content of the WMP increased such changes have significant implications for the mouthfeel and smoothness of chocolate. For more information on the role of fat in milk powder, see Chapter 13... 

Block chocolate in which molten chocolate is cast into moulds and solidified in... 

Enrobed sweets in which centres are covered in molten chocolate before cooling ... 

FIGURE 8.15 Relationship among shear stress, viscosity, and shear rate as flow behavior of molten chocolate for 1 the temperature is 35°C, and for 2 it is 45°C (arbitrary scale). 

Chocolate can be characterized by a yield stress and plastic viscosity, i.e., as the Bingham plot. Another curve was established by Casson and reported by Holdsworth (1971) in which chocolate is characterized by the yield value and plastic viscosity. The Bingham plot is mainly used for process design and its control in the production of plain chocolate. In the case of Casson plots, some molten chocolates, particularly those containing active surface agents, did not give straight-line relationships. To overcome this difficulty, another expression was developed (Elson, 1977) ... 

The flow behavior of molten chocolate can also be affected by changes in processing conditions. These may lead to different values, because of the effect of non-Newtonian flow at the walls of the processing equipment. The wall shear rate is often characterized by the Nusselt number equation, which contains the so-called <5 factor. The S factor is the ratio of the wall shear rate for a non-Newtonian fluid to that of a Newtonian fluid at the same flow rate. For power law fluids, this factor can be calculated ... 

This model has often been used for describing the steady shear stress-shear rate behaviom of blood, yoghurt, tomato pme6, molten chocolate, etc. The flow behaviom of some particulate suspensions also closely approximates to this type of behaviom. 

A molten chocolate (density = 1500kg/m ) flows through a concentric annulus of inner and outer radii 10 mm and 20 mm, respectively, at 30°C at the constant flow rate of 0.03 m /min. The steady-shear behaviour of the chocolate can be approximated by a Bingham plastic model with xf = 35Pa and /xg = 1 Pa-s. 

Two observations can be made here. The 25% reduction in the available pressure gradient has lowered the flow rate by 31%. Secondly, in this case the flow rate is only one tenth of that of a Newtonian fluid of the same viscosity as the plastic viscosity of the molten chocolate ... 

Synonyms Phosphatidic acid, ammonium salt Definition Ammonium salts of phosphatidic acids derived from edible fats and oils Properties Unctuous semisolid sol. in fats partly sol. in ethanol insol. in water Uses Emulsifier in foods, dairy-based beverages vise, control agent for molten chocolate, substitute for soya lecithin in cocoa, chocolate prods., confectionery Features Flavor-free Ammonium phosphite CAS 51503-61-8... 

Workers who handle molten chocolate favour the Casson model blood is also believed to conform to this model. 

Figure 1 Flow curve of molten chocolate measured in a vane geometry to eliminate slip.

Together with lecithin, PGPR is used in the production of chocolate. It completely eliminates the flow point of a molten chocolate mass, but hardly lowers the viscosity. 

This covers a wider range of fluids than that of the Bingham plastic and so there are numerous examples of these yield pseudoplastic materials quoted in texts, including mayonnaise, ketchup, some printing inks, molten chocolate, plastic explosives, blood, water-coal mixtures, foams, battery and rocket propellant pastes, and drilling muds. 

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