Sorting and grading in food processing, Lecture notes of Food Science and Technology

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Sorting & Grading

Prepared By: Ms Kulsum Ibrahim

Learning Objectives

O To have better understanding of

sorting and grading.

O To have keen knowledge about

method of sorting and criteria of

grading.

O (^) There are a number of benefits, including the need for sorted units in weight-filling operations and the aesthetic and marketing advantages in providing;  (^) units of uniform size or colour.  (^) much easier to control processes such as sterilisation, dehydration or freezing in sorted food units  (^) and they are also better suited to mechanised operations such as size reduction, pitting or peeling.

Methods of Sorting O (^) Sorting is carried out on the basis of individual physical properties. No sorting system is absolutely precise and a balance is often struck between precision and flow rate. O (^) Following are the methods of sorting;  (^) Weight sorting  (^) Color sorting  (^) Size and shape sorting etc.

Size sorting O (^) The size and shape of food units are difficult to define precisely so It is less precise than weight sorting, but is considerably cheaper. O (^) Size categories could involve a number of physical parameters, including;  (^) diameter,  (^) Length  (^) or projected area. O (^) Diameter of spheroidal units such as tomatoes or citrus fruits is conventionally considered to be orthogonal to the fruit stem, while length is coaxial. Therefore rotating the units on a conveyor can make size sorting more precise.

Size sorting: O (^) Sorting into size categories requires some sort of screen with many designs. O (^) The main categories of screens are fixed aperture and variable aperture designs. O (^) Flatbed and rotary screens are the main geometries of the fixed bed screen and a number of screens may be used in series or in parallel to sort units into several size categories simultaneously. O (^) Fixed screens are often used with smaller particulate foods such as nuts or peas.

Color sorting O (^) Color/photometric properties are often a measure of maturity, presence of defects or the degree of processing. O (^) Manual colour sorting is carried out widely on conveyor belts or sorting tables, but is expensive. O (^) The process can be automated using highly accurate photocells which compare reflectance of food units to preset standards and can eject defective or wrongly coloured, e.g. blackened, units. O (^) This system is used for small particulate foods such as beans or maize kernels for canning, or nuts, rice and small fruit. O (^) Colour sorting can also be used to separate materials which are to be processed separately, such as red and green tomatoes. It is feasible to use transmittance as a basis for sorting although, as most foods are completely opaque.

Grading O (^) Grading is classification on the basis of quality, incorporating commercial value, end use and official standards and hence requires that some judgement on the acceptability of the food is made, based on simultaneous assessment of several properties, followed by separation into quality categories. O (^) Appropriate inspection belts or conveyors are designed to present the whole surface to the operator. O (^) Trained manual operators are frequently used to judge the quality, and may use comparison to charted standards. O (^) For example, a fruit grader could simultaneously judge shape, colour, evenness of colour and degree of russeting in apples. Egg candling involves inspection of eggs spun in front of a light so that many factors, including shell cracks, diseases, blood spots or fertilisation, can be detected.

Reference O (^) Seaton, H.L. 1955, Scheduling plantings and predicting harvest maturities for processing vegetables, Food Technology 9, 202–209. O (^) 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. O (^) Mohsenin, N.N. 1989, Physical Properties of Food and Agricultural Materials, Gordon and Breach Science Publishers, New York. O (^) Chung, O.K., Pomeranz, Y. 2000, Cereal Processing, in Food Proteins: Processing Applications, ed. S. Nakai, H.W. Modler, Wiley-VCH, Chichester, pp. 243–307. O (^) Nakai, S., Wing, P.L. 2000, Breadmaking, in Food Proteins: Processing Applications, ed. S. Nakai, H.W. Modler, WileyVCH, Chichester, pp. 209–242. O (^) Dobraszczyk, B.J. 2001, Wheat and Flour, in Cereals and Cereal Products: Chemistry and Technology, ed. D.A.V. Dendy, B.J. Dobraszczyk, Aspen, Gaithersburg, pp. 100–139.

Thank You