Dry cleaning method in processing, Lecture notes of Food Science and Technology

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Raw Material

Cleaning

By Miss Kulsoom Ibrahim

 (^) To learn about the cleaning.  (^) Types of dry cleaning methods.

Learning Objectives

The main contaminants are:

• unwanted parts of the plant such as leaves, twigs, husks;
• soil, sand, stones, and metallic particles from the growing area;
• insects and their eggs;
• animal excreta, hairs, and so on;
• pesticides and fertilizers;
• mineral oil;
• microorganisms and their toxins.

Main contaminants

 (^) The main dry cleaning methods are based on screens, aspiration, or magnetic separations.  (^) Dry methods are generally less expensive than wet methods  (^) Less effective in terms of cleaning efficiency.  (^) A major problem is recontamination of the material with dust.  (^) Precautions may be necessary to avoid the risk of dust explosions.

Dry Cleaning Methods

Screening

 (^) This exploits the differences in aerodynamic properties of the food and the contaminants.  (^) It is widely used in the cleaning of cereals, but is also incorporated into equipment for cleaning peas and beans.  (^) The principle is to feed the raw material into a carefully controlled upward air stream.  (^) Denser material will fall, while lighter material will be blown away depending on the air velocity.  (^) By using different air velocities, it is possible to separate, wheat from lighter chaff or denser small stones.

2) Aspiration

 (^) Very accurate separations are possible, but large amounts of energy a required to generate the air streams.  (^) Obviously the system is limited by the size of raw material units, but is particularly suitable for cleaning legumes and cereals.

Continue..

 (^) This can be used in a limited number of cases where the surface charge on raw materials differs from contaminating particles.  (^) The principle can be used to distinguish grains from other seeds of similar geometry but different surface charge, and has also been described for cleaning tea.  (^) The feed is conveyed on a charged belt and charged particles are attracted to an oppositely charged electrode according to their surface charge.

4) Electrostatic cleaning

 (^) 1. Seaton, H.L. (1955) Scheduling plantings and predicting harvest maturities for processing vegetables. Food Technol., 9, 202–209.  (^) 2. Maestrelli, A. (2000) Fruit and vegetables: the quality of raw material in relation to freezing, in Managing Frozen Foods (ed. C.J. Kennedy), Woodhead Publishing, Cambridge, pp. 27–55.  (^) 3. Mohsenin, N.N. (1989) Physical Properties of Food and Agricultural Materials, Gordon and Breach Science Publishers, New York.  (^) 4. Kader, A.A. (2008) Perspective: flavour quality of fruits and vegetables. J. Sci. Food Agric., 88, 1863–1868.  (^) 5. Chung, O.K. and Pomeranz, Y. (2000) Cereal processing, in Food Proteins: Processing Applications (eds S. Nakai and H.W. Modler), Wiley-VCH Verlag GmbH, Weinheim, pp. 243–307.

Reference