Controlling the Flow Properties of Liquid Chocolate

The flow properties of liquid chocolate are important to the consumer and the confectionery manufacturer. Although there are many very sophisticated instruments for measuring viscosity and texture, the human mouth is really far more sensitive than most of these. When someone eats chocolate, the teeth bite through the solid chocolate. This means that the hardness of the solid chocolate is very important. The temperature of the mouth, at about 37 1C, is above the melting point of the fat within the chocolate, so it rapidly melts, especially as it is subjected to the intense mixing and shearing of the teeth and tongue. Once it has melted there are two important factors. One is the maximum particle size. As was noted earlier, if there is a significant number of particles larger than 30 microns (0.03mm) the chocolate will feel gritty on the tongue. In addition, for sizes below 30 micron a difference of 2–3 microns in maximum particle size can be detected as different levels of smoothness. Chocolates with a maximum particle size of about 20 microns have been sold as having a silky texture. The second factor is the viscosity. This not only affects the way the chocolate runs around the mouth, i.e. the texture, but it also changes the taste. This is because the mouth contains three different flavour receptors in different places (see Figure 5.1). The time the solid particles in the chocolate take to reach the receptors depends on the viscosity. This means that two chocolates made from identical ingredients, but processed to give different viscosities, will taste very different. (See Project 15 in Chapter 12). Particle size affects viscosity as well as texture, and a milk chocolate which has been milled to say a maximum particle size of 20 microns will have a creamier taste and texture than one of 30 microns.
For the manufacturer, the weight control of the products is very important. Chocolate is a relatively expensive food in terms of both ingredients and processing. It is therefore economically important not to put too much chocolate on a confectionery centre. As will be shown in Chapter 7, the coating methods rely on the liquid chocolate having the correct viscosity. In addition, if the coating is not put on correctly, misshapes will be formed (see Figures 4.2 and 4.3), or the centre will be exposed reducing the shelf life of the product.

Reference: The Science of Chocolate