ABSTRACT
There are two main methods of making dispersions. One is supersaturation of the continuous phase with the component that is to become the disperse phase. This involves the processes of nucleation (Chapter 14) and growth (Chapter 15 for solids). The particles can be obtained in a wide range of sizes. The method is applied in food processing, for instance to obtain sugar crystals that are subsequently separated from the liquid, or to make a plastic fat-a dispersion of aggregated fat crystals in oil. The other method involves dividing a material into small particles that are then suspended in a liquid. Making suspensions of solid materials is done by dry or wet grinding, which tends to be a very difficult operation if small particles are desired. The theory involves fracture mechanics and shows that it is very difficult to break up small particles into still smaller ones, which is also observed in practice (see Section 17.1.2). An example of the process is the lengthy milling of the (liquid) cocoa mass in chocolate manufacture to obtain very small sugar particles (about 10 µm).
