Sorting separates foods based on a single measurable property like size, weight, or color. Grading assesses overall quality using multiple attributes and properties. Both operations upgrade products. Common sorting methods include weight, size, shape, density, and color sorting using sensors, cameras and machines. Grading requires human or trained assessment of quality factors like appearance, defects, and standards. It assigns foods to quality categories while sorting separates based on a single criterion.

1. FOOD PROCESSING AND
PRESERVATION
PBS-FPP-311

2. SORTING AND GRADING
 Sorting and grading are terms which are frequently
used interchangeably in the food processing industry,
but strictly speaking they are distinct operations.
 Sorting is a separation based on a single measurable
property of raw material units, while grading is ‘‘the
assessment of the overall quality of a food using a
number of attributes’’.
 Grading of fresh produce may also be defined as
‘‘sorting according to quality,’’ as sorting usually
upgrades the product.

3. SORTING AND GRADING
 There are a number of benefits, including the need for
sorted units in weight filling operations, and the aesthetic
and marketing advantages in providing uniform-sized or
uniform-colored units.
 In addition, it is much easier to control processes such as
sterilization, dehydration, or freezing in sorted food units
 They are also better suited to mechanized operations such
as size reduction, pitting, or peeling.

4. SORTING
 Just like cleaning, sorting should be employed as early
as possible to ensure uniform product for subsequent
processing
 Sorting may therefore be used as part of grading but
not vice versa
 Sorting can be done manually or using automated
systems like conveyor belts with sensors, cameras, or
mechanical sorting machines.

5. SORTING
 The four main physical properties used to sort foods are
 Size – Ensures uniformity in products like fruits, vegetables, grains,
and nuts. using mechanical
 Shape -
 Weight -
 Color - Removes defective or discolored items, enhancing the overall
appearance of the product.
 Quality Sorting: Detects and removes damaged, rotten, or otherwise
unsuitable items from the production line
 Ripeness Sorting: Separates items based on their level of ripeness,
ensuring consistent quality in products like fruits and vegetables.

6. METHODS OF SORTING
1. Weight sorting
 This is usually the most precise method of sorting, as it is
not dependent on the geometry of the products.
 Eggs, fruit, or vegetables may be separated into weight
categories using spring-loaded, strain gauge, or electronic
weighing devices incorporated into conveying systems.
 Using a series of compressed air blowing mechanisms set to
trigger at progressively lesser weights, the heavier items are
removed first followed by the next weight category, and so
on.
 These systems are computer controlled and can additionally
provide data on quantities and size distributions from
different growers.
 A disadvantage of weight sorting is the relatively long time
required per unit

7. SORTING
2. Size sorting
 This is less precise than weight sorting, but is
considerably cheaper.
 The sizes and shapes of food units are difficult to define
precisely.
 Size categories could include a number of physical
parameters including diameter, length, or projected area.
 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

8. SORTING AND GRADING
3. Shape sorting
 This is useful in cases where the food units are
contaminated with particles of similar size and weight.
 This is particularly applicable to grain which may contain
other seeds.
 The principle is that disks or cylinders with accurately
shaped indentations will pick up seeds of the correct
shape when rotated through the stock, while other shapes
will remain in the feed

9. SORTING AND GRADING
4. Sorting according to density
 This can be a marker of suitability for certain processes.
 The density of peas correlates well with tenderness and
sweetness, while the solids content of potatoes, which
determines suitability for manufacture of crisps and dried
products, relates to density.
 Sorting on the basis of density can be achieved using
flotation in brine at different concentrations.

10. SORTING AND GRADING
5. Color sorting
 Photometric properties (color) may be used as a basis for
sorting.
 Color is often a measure of maturity, presence of defects, or the
degree of processing.
 Manual color sorting is carried out widely on conveyor belts or
sorting tables, but is expensive.
 The process can be automated using highly accurate photocells
which compare reflectance of food units to preset standards,
and can eject defective or wrongly colored units,
 This system is used for small particulate foods such as navy
beans or maize kernels for canning, or nuts, rice, and small
 Color sorting can also be used to separate materials which are
to be processed separately such as red and green tomatoes.

11. COLOR SORTER

12. EFFECTIVENESS OF SORTING PROCEDURE
Effectiveness=PXpR(1-Xr)
FXfF(1-Xf)
Where;
P(kgs-1
)=Productflowrate
F(kgs-1
)=Feedflowrate
R(kgs-1
)=Rejectedfoodflowrate
Xp=Massfractionofdesiredmaterialinproduct
Xf=Massfractionofthedesiredmaterialinthefeed
Xr=Massfractionofdesiredmaterialintherejectedfood

13. SORTER PERFORMANCE
 The performance of a sorter is described based on the
following 3 criteria
1. Defect removal efficiency - % of defective incoming
product that the system removes. It is a measure of
its ability to remove the product that does not meet
expectations
2. Recovery efficiency - % of acceptable incoming
product that leaves the system in the acceptable
stream. It shows false accept/false reject
performance
3. Throughput – maximum amount of material that
the system can sort without losing performance in
defect removal and recovery efficiencies

14. GRADING
▪ Grading is classification on the basis of quality
(incorporating commercial value, end-use, and official
standards), and hence requires that some judgment on the
acceptability of the food is made, based on simultaneous
assessment of several properties, followed by separation
into quality categories.
▪ This can be done by human graders who assess the quality
of random samples of foods (by also laboratory analysis)
▪ Appropriate inspection belts or conveyors designed to
present the whole surface to the operator, are frequently
used

15. GRADING
▪ Trained manual operators are frequently used to judge
the quality, and may use comparison to charted
standards, or even plastic models.
▪ For example, a fruit grader could simultaneously judge
shape, color, evenness of color, 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 fertilization, can
be detected.
▪ Apparently, experienced candlers can grade thousands
of eggs per hour.
▪ Machine grading is only feasible where quality of a food
is linked to a single physical property, and hence a
sorting operation leads to different grades of material.
▪ Size of peas, for example, is related to tenderness and
sweetness, therefore size sorting results in different
quality grades