At the heart of transforming raw ingredients into food for human consumption is the mixing operation. It’s a main task which other food processing steps also share to establish consistency. Whether a food product requires small-scale mixing by hand or high volume blending of multiple ingredients, home cooks and food process engineers alike know the importance of proper mixing. Even with the right amount of ingredients and flavors, a great recipe will not transform into good food unless the components are well-mixed. Taste, texture, color, appearance – these are all crucial parameters intimately influenced by the mixing process. Consumers expect that the food products they patronize will be exactly the same as the one they had last. It is easy to understand that within the food industry a high level of consistency is required not just batch-to-batch but facility-to-facility. In this market, consistency is the backbone of consumer loyalty. 1.1
Mixing is the dispersing of components, one throughout the other. It occurs in innumerable instances in the food industry and is probably the most commonly encountered of all process operations. It can also be defined as the intermingling of two or more dissimilar portions of a material resulting in the attainment of a desired level of uniformity either physical or chemical in the final product (Lindley, 1991). Mixing is achieved by imparting forces to the mixture which creates motion. Very often, mixing occurs simultaneously with size reduction, as is the case in forming, homogenizing and emulsification. Mixing increases the homogeneity of a system by reducing non-uniformity or gradients in composition, properties or temperature. Besides the primary objective of homogeneity, secondary objectives of mixing include control of heat and mass transfer rates, reactions and structural changes (Harnby et al. 2001). Mixing ensures delivery of a product with constant properties. Mixing may lead to particle fracture or deformation which is an undesirable change. If mixing fails to achieve the required product yield, quality, organoleptic or functional attributes production costs may increase significantly. Mixing has no preservative effect and is intended solely as a processing aid or to alter the eating quality of foods. It has very wide applications in many food industries where it is used to combine ingredients to achieve different functional properties or sensory characteristics. Examples include texture development in dough’s and ice cream, control of sugar crystallization and aeration of batters and some chocolate products. 1.3
Problems or need for knowledge about mixing
The complex rheological challenges arising from non-Newtonian food materials and the inclusion of large particles have not been sufficiently investigated. The complex rheology of food products can influence the effectiveness of a given geometry to achieve the desired mixing outcomes. Food mixing can involve ingredients of different physical properties and quantities. Food materials mixed may range from nanoemulsions, to large particulate suspensions, to highly viscous pastes or dry powders. The wide variety of particulates with different sizes, shapes and strengths used in the food industry can result in major segregation issues. Producing particulates with similar sizes, agglomerating ingredients or reducing vibration during transport can all help reduce these segregation problems. Many unique design challenges apply to food mixing as food properties such as texture, flavour, shelf-life and safety must also be considered. The effectiveness of mixing can be assessed only in the context of the quality of the end product. Mixer design is slowly changing from a complete experimental process to a partially numerical and experimental one. There is a need to develop and evaluate new in-line mixers to meet the requirements of the food industry, where there is an increasing trend...
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