Separation processes-an overview 5 complexity and diversity which provides the scope and potential for separating selected Table 1.3. Examples of physical properties of foods, and separation processes to which they relate Physical property Separation technique Size, size distribution, shape Screening, air classification Density Centrifugation Liquid extraction processes rheologica Surface properties Froth flotation Thermal properties Evaporation, Electrical Electrostatic sorting Membrane separations Solubility Solvent extraction Thermal denaturation Optical Reflectance(colour)sorting 1.2 SEPARATION TECHNIQ 1. 2.1 Introduction Separation of one or more components from a complex mixture is a requirement for many operations in the food and biotechnology industries. The components in question range from particulate materials down to small molecules, The separations usually aim to achieve removal of specific components, in order to increase the added value of the products, which may be the residue, the extracted components or both. All separations rely on exploiting differences in physical or chemical properties of the mixture of compo- nents. Some of the more common properties involved in separation processes are partick or molecular size and shape, density, solubility and electrostatic charge. These properties re discussed in more detail elsewhere(Mohsenin, 1980, 1984: Lewis, 1990). In some operations, more than one of these properties are involved. However, most of the processes involved are of a physical nature Separation from solids or liquids involves the transfer of selected components across the boundary of the food. In many processes another stream or phase is involved, for example in extraction processes. However, this is not always so, for example expression, centrifugation or filtration. In expression, fruit juice or oil is squeezed from the food by application of pressure. In centrifugation, fat can be separated from water due to thei density differences, by the application. of a centrifugal force, In filtration there is a physical barrier to the transfer of certain components and the liquid is forced through the barrier by pressure, whilst the solids are retained. The resistance to flow will change throughout the filtration process, due to solids build-up. It can be seen that main drivingSeparation processes - an overview 5 complexity and diversity which provides the scope and potential for separating selected components from foods. Table 1.3. Examples of physical properties of foods, and separation processes to which they relate Physical property Separation technique Size, size distribution, shape Screening, air classification Density Centrifugation Viscosity Liquid extraction processes Rheological Expression Surface properties Froth flotation Thermal properties Evaporation, drying Electrical Electrostatic sorting Diffusional Extraction Solubility Solvent extraction Optical Reflectance (colour) sorting Membrane separations Thermal denaturation 1.2 SEPARATION TECHNIQUES 1.2.1 Introduction Separation of one or more components from a complex mixture is a requirement for many operations in the food and biotechnology industries. The components in question range from particulate materials down to small molecules. The separations usually aim to achieve removal of specific components, in order to increase the added value of the products, which may be the residue, the extracted components or both. All separations rely on exploiting differences in physical or chemical properties of the mixture of compo￾nents. Some of the more common properties involved in separation processes are particle or molecular size and shape, density, solubility and electrostatic charge. These properties are discussed in more detail elsewhere (Mohsenin, 1980, 1984; Lewis, 1990). In some operations, more than one of these properties are involved. However, most of the processes involved are of a physical nature. Separation from solids or liquids involves the transfer of selected components across the boundary of the food. In many processes another stream or phase is involved, for example in extraction processes. However, this is not always so, for example expression, centrifugation or filtration. In expression, fruit juice or oil is squeezed from the food by application of pressure. In centrifugation, fat can be separated from water due to their density differences, by the application of a centrifugal force. In filtration there is a physical barrier to the transfer of certain components and the liquid is forced through the barrier by pressure, whilst the solids are retained. The resistance to flow will change throughout the filtration process, due to solids build-up. It can be seen that main driving