Factors Affecting the Flow properties of Chocolate
A major reason for being able to measure the viscosity of chocolate is to
be able to correct it, when production difficulties occur. Some may relate to
the yield value rather than the plastic viscosity and vice versa. It is therefore
important to know which factors affect the flow property concerned, in order
to correct it.
Fat content
It is useful to consider the micro-structure of chocolate in order to understand how it flows. This is illustrated schematically in Figure 10.13. It is the liquid fat (both cocoa butter and milk fat) that enables the chocolate to flow. In weight terms it constitutes about one third of the chocolate, but in volume terms (because fat has a lower density) it is almost half. As the fat content increases the distance between the solid particles increases so the viscosity
drops. Some of the fat is bound by and within the particles, so does not aid the flow. If a chocolate is too thick, the further grinding of the cocoa liquor or the use of an alternative milk powder source should be considered.
It is the free fat that enables the chocolate to flow and if the total fat content is low (e.g. about 25%), then the proportional increase in free fat content of an extra 1% of cocoa butter is going to be a lot greater than for one with 35% fat content. This means that the effect on viscosity of additional cocoa butter is much greater at lower fat contents and
becomes very small indeed above 35% (see Figure 10.14; (Chevalley,1999). The yield value arises mainly from the inter-particle reactions,which means that it is less affected than the yield value by the addition of fat. Where the yield value is incorrect other factors should be
investigated.
All the factors tend to be interrelated. In Figure 10.14 it can be seen that the magnitude of the effect of adding extra fat depends upon the particle size
Schematic representation of the solid particles and fat within a milk chocolate
