Post Harvest Management of Horticultural Crops

Sorting sizing and grading

SORTING, SIZING AND GRADING

Sorting

Sorting is done by hand to remove the fruits and vegetables which are unsuitable to market or storage due to damage by mechanical injuries, insects, diseases, immature, over-mature, misshapen etc. This is usually carried out manually and done before washing. By removing damaged produce from the healthy ones, it reduces losses by preventing secondary contamination. Sorting is done either at farm level or in the pack-houses. In sorting, only sensory quality parameters are taken into consideration.

The following illustrations represent three types of conveyors used to aid sorting of produce.



Sizing

Before or after sorting, sizing is done either by hand or machine. Machine sizers work on two basic principles; weight and diameter. Sizing on the basis of fruit shape and size are most effective for spherical (oranges, tomato, certain apple cultivars) and elongated (Delicious apples and European pears are of non-uniform shape) commodities, respectively.



Mechanisms/Types of sizing

A. Diverging belts/rope grader - the different speed of belts makes produce rotate besides moving forward to a point where produce diameter equals belt/rope

separation. Eg. cucumbers, gherkins, pineapples and large root vegetables(fig.8).

B. Sizing rollers - with increased spaces between rollers (fig.9) Eg. Citrus
C. Hand held template-Sizing can be performed manually using rings of known diameter (fig.11).
D. Sizing by weight - sorting by weight is carried out in many crops with weight sensitive trays. These automatically move fruit into another belt aggregating all units of

the same mass. Individual trays deposit fruit on the corresponding conveyor belt (fig.10). Eg. Citrus, apples and pear and irregular fruits

E. Mesh screens - eg, potato, onion, anola etc.










Grading

The produce is separated into two or more grades on the basis of the surface colour, shape, size, weight, soundness, firmness, cleanliness, maturity & free from foreign matter /diseases insect damage /mechanical injury.

For eg.: Apple I. Extra Fancy II. Fancy III. Standard IV. Cull (for processing).

Grading may be done manually or mechanically. It consists of sorting product in grades or categories based on weight/size.


Systems of grading : Static and Dynamic.

A. Static systems - are common in tender and/or high value crops. Here the product is placed on an inspection table where sorters remove units which do not meet the requirements for the grade or quality category (fig.12).

B. The dynamic system - here product moves along a belt in front of the sorters who remove units with defects (fig.13). Main flow is the highest quality grade. Often second and third grade quality units are removed and placed onto other belts. It is much more efficient in terms of volume sorted per unit of time. However, personnel should be well trained. This is because every unit remains only a few seconds in the worker's area of vision. Eg. Onion grading

There are two types of common mistakes: removing good quality units from the main flow and more frequently, not removing produce of doubtful quality



New Innovation in grading systems

i. Computerized weight grader – operate on the basis of tipping buckets that drops to release the pre weighed item at a particular position. – Apples, citrus
ii. Video image capture &analysis–used for size, colour &external defect grading-coffee bean, apple
iii. NIR Spectrometers – to assess the TSS non – destructively in apple and stone fruits
iv. X-ray imaging and Computer aided tomography
v. MRI - Magnetic Resonances Imaging
vi. Spectroscopy
vii. Acoustic methods
viii. Volatile emission analysis