mechanical seperation in food

by chandresh

1. Mechanical separation in food By-Praveen Tiwari

2. Definition- Mechanical- operated by a machine or machinery. Separation- it is a method to achieve any phenomenon that converts a mixture of chemical substance into two or more distinct product mixtures, which may be referred to as mixture, at least one of which is enriched in one or more of the mixture's constituents. In some cases, a separation may fully divide the mixture into its pure constituents. 

3. Introduction- Mechanical separation in food processing include two main operations i.e. removal of substances or material and their classification. Mechanical separation equipment is used extensively in food manufacturing, preservation or preparatory operation. Mechanical separation are based on differences of density and size/shape of the food particles/pieces.

4. Separation table

5. Process involved Mechanical separations can be divided into four groups – sedimentation, centrifugal separation, filtration and sieving.

6. 1. sedimentation It is settling of matter to the bottom of a fluid so as to separate suspended solids from fluids. Sedimentation is very often used in the food industry for separating dirt and debris from incoming raw material, and dust or product particles from air streams.

7. 1.1 Sedimentation of Particles in a Gas An important application, in the food industry, of sedimentation of solid particles occurs in spray dryers. In a spray dryer, the material to be dried is broken up into small droplets of about 100 micro m diameter and these fall through heated air, drying as they do so. The necessary area so that the particles will settle can be calculated in the same way as for sedimentation.

8. 2. Centrifugal separation Centrifugal separation or centrifugation is a process in which two heterogeneous mixtures of phases are separated from each other by the application of centrifugal force. The phases may be solid, liquid or gas. The basic principle governing is the density difference.

9. 2.1 Solid-liquid separation The fruit fibres are suspended in juice. Sugar is crystallized from the solution and separated thereafter. The solid matter either floats or settles in the tank in due course of time because of the density difference between the two phases. To achieve quick settling centrifugal force is used, and the process is called centrifugal settling .

10. Centrifugal filtration allowing the slurry through a porous medium. The rate of separation depends on the particle size of the slurry, the pore size of the filter medium and the pressure differential at both side of the filter medium. the filters are attached concentrically to the cylindrical bowl and the flow of liquid is horizontal unlike normal filtration process. can be batch or continuous types.

11. 2.2 Liquid-liquid separation Because of density differences, the lighter liquid separates from the heavier liquid, if allowed to stand for some time. Milk is a good example of emulsion where fat is in the finely dispersed state where as the skim milk is in continuous phase.

12. 2.3 Solid-gas separation Solid particulates separation from a gas stream is very common phenomenon in food processing operations. The separation of milk powder from the drying air stream coming from the drying chamber of a spray dryer after drying is a good example of solid-gas separation. The peripheral attachment required for this operation to accomplish is called cyclone separator.

13. 3. Filtration Filtration is a unit operation where separation of insoluble solids from a solid-liquid suspension is done with the application of mechanical or gravity force through a porous membrane. The solids are retained in the porous medium and form a layer, called filter cake. The driving force for the separation of the two phases may be gravity force or mechanical force.

14. 3.1 principle of operation The driving force for filtration is most often the pressure difference. In the beginning of the filtration process, filtrate flows easily through the medium with least resistance. The rate of filtration which is the ratio of filtrate volume and time of filtration is high in the beginning. But, as the filtration progresses, the layer of cake deposition upstream gradually increases.

15. 4. Sieving During sieving the sample is subjected to horizontal or vertical movement in accordance with the chosen method. This causes a relative movement between the particles and the sieve; depending on their size the individual particles either pass through the sieve mesh or are retained on the sieve surface. Sieve shakers are used for mechanical sieving.

16. Why to use mechanical separation? To save time, Cost efficient method, Increases efficiency, Can used for wide range of application, etc.