1. Cleaning, sorting and grading of Potato
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2. Introduction Cleaning
Cleaning refers to removal of undesirable material from the surface of potato tubers. In potato, cleaning mainly aims at removal of the adhering soil alongwith the microorganisms carried by the soil.
Sorting
Sorting in potato would refer to removal of rotten, diseased, infected and cut fruits.
Grading
Grading in potato would refer to categorization of fruits based on their size, shape etc.

3. Sequence of operation in potato
Harvesting
Drying
Curing
Storage and marketing
Grading
Sorting
Consumer

4. Care and precautions in potato
A) During drying:
(a) Always dry the harvested tuber quickly to remove excess moisture from the surface of tubers for improving their keeping quality.
(b) Always dry the harvested tuber in storage shed, expose to sun causes the greening of potatoes.
(c) Do not store the tubers immediately if they are exposed to rain after harvest.
B) During curing:
(a) Always follow the curing process at 25 degree centigrade with a 95 per cent relative humidity,
(b) For optimum suberization, curing is essential for healing the wounds of tubers resulted from cutting and bruising during harvesting.
C) During sorting:
All the damaged and diseased tubers should be removed during sorting.
(Source: AGMARK (2011)

5. Sorting
Source:
Source: AGMARK (2011)

6. Manual Sorting
Generally potato tubers are cleaned by drying and shedding off the soil adhering to the surface of tubers.
Sometimes washing in water may also be done.
Excess of moisture from the surface of potato tubers should be removed before storage by curing.
In India, workers sit close to piled potato heap and sort damaged, diseased and green potatoes by hand.

7. What type of tubers are to be separated during sorting?
Damaged tubers
Green potatoes
Diseased tubers
Cut potatoes

8. Mechanical Method
Cleaning, sorting and grading may be done manually as well as by using specific machines. During mechanical operation, potato tubers are conveyed through a belt conveyor. Workers stand on both sides of the belt, pick up the undesirable tubers and put it on another belt conveyor which separated the desirable from the undesirable tubers. Click here to see the visual.
Specific machines for washing potato are also available
Source:
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9. Are the three operations cleaning, sorting and cutting different ??
The three operations are different but in potato generally, these three operations or pre-treatments go on simultaneously.
How do we grade potatoes ???
Potatoes are generally graded according to their size. The common grades for potato are:
In 4 Grades (weight in g)
In 6 grades(weight in g) 1
< 10 2
10-25 3
25-60
25-50 4
> 60
50-75 5
75-100 6
>100

10. Benefits of Grading Potato
i) Grading helps the potato producer and seller to influence the determination of price.
ii) It reduces the cost of marketing and helps the consumers to get standard potato at fair price.
iii) It facilitates the scope for potato export.
iv) It has a direct influence on utilization point of view, as the small to medium sized tubers are prepared for ‘seed tubers’ and large sized tubers are preferred for processing purpose.
Source: AGMARK (2011)

11. Methods of Grading :
Grading of tubers is done both by hand as well as by graders. The different practices of grading of potato are as follows:
i) Grading with a set of rectangular sieves having round holes of varying diameters, where a pair of such sieves placed one above the other are shaken to and fro by two persons and the third person continuously feds the upper sieve.
ii) Grading through sieves hung on chains or ropes and move back and fore.
iii) Grading by mechanical grader, where sieves are mounted on oscillation of frame as operated mechanically by power. This grader can be operated with 1H.P. electric motor, engine or tractor.
iv) Grading with power operated potato grader with conveyer attachment gives better grading efficiency (90 per cent). The power requirement is 1.5 H.P. The rubber roller type of potato grader grades, six categories of grades. The system consist of mainframe, grading rollers, conveyor belt and power transmission system. The grader is operated by 2 H.P electric motor.
Source: AGMARK (2011)

14. Let us sum up
Potato is the main vegetable crop in India and a staple food in many of the European countries.
Drying, curing, sorting and grading are important operations in potato after harvesting
Cleaning of potato refers to removal of undesirable material i.e. adhering soil along with the microorganisms carried by the soil while, Sorting in potato would refer to removal of rotten, diseased, infected and cut fruits.
Grading in potato would refer to categorization of fruits based mostly on their size / weight into 4 to 6 categories through rectangular sieves.