Post Harvest Operations

Introduction Physio Chemical Changes in Potato during Storage Factors Governing Safe Storage of Potatoes Five basic requirements for safe storage of potatoes Storage Design Cooling Systems and Equipment Uses of Potatoes in Indian Kitchens


    Ten factors that govern storage life of Potatoes

    • Prevailing climatic conditions
    • Variety and maturity of tubers
    • Incidence of infection at the time of harvesting
    • Extent of damage to tubers prior to storage
    • Time interval between harvesting and storage
    • Storage temperature and humidity
    • Air circulation in storage chamber
    • Co2 concentration in chamber
    • Sanitary conditions in cold storage
    • Treatment of tubers before storage.


Physio-chemical changes in tubers during storage

Sprouting of Tubers

  • Sprouting is unwanted germination of tubers. It starts at temperatures more than 50 deg F in storage.
    • If more light falls on tubers at 40 deg F, it also starts growing in tubers. It reduces
    1. Storage life
    2. Level of vitamin C
    3. Quality of cooking, processing and germination
    4. It also changes chemical composition.

Greening of Tubers

  • Greening in potatoes is being induced when they are exposed to light continuously for sometime.
  • The colour becomes green and taste bitter. The growing occurs:
    1. Glycoalboloid
    2. Solenine
    3. Chaconine

It deteriorates the quality of cooking and changes chemical composition of Tubers also.

Sweetening of Tubers

  • When potatoes are stored at temperature below 35 deg F, the starch starts converting into sugar by which tubers become sweet.
  • The accumulation of sugar changes the peeled tubers to brown and chips become black. If respiration rate is low, sweetening will be high. This changes flavor and quality of potatoes.

Rotting of Tubers

    • The rotting of tubers is caused by micro-organisms entered in peeled, cut, bruised and contaminated tubers in presence of favorable conditions available for their survival. It results
      1. Odour becomes foul
      2. Eyes become black
      3. When they are pressed, leak water
  • Black heart is caused due to abnormal rate of respiration in poor ventilation and fungus causing blight grows in tubers which are stored at low temperature for 10-15 days. Any bruise on tubers may cause infection by leak fungus.


Factors Governing Safe Storage of Potatoes

Potato Conditions

Tuber Variety

  • The autumn crop can resist a wide range of temperature and withstand low humidity.
  • While crop is not capable of tolerating higher temperatures.
  • Kufri sheetman can tolerate frost and low temperatures, while Kufri Sandhuri higher temperatures.

Tuber Maturity

  • Mature tubers can be stored for long period under safe storage conditions while immature tubers are easily affected by fluctuations in environmental conditions and infected by micro-organisms.

Tuber Health

The potatoes free from mechanical injuries like cuts, bruises and scraping as well as from biological injuries like

  • Disease Infection
  • Insect Attack
  • Rotten Condition
  • Sprouting

Can be stored for longer periods as compared to unhealthy tubers

Handling Conditions

Careful Handling

  • During harvesting, grading, plucking and stacking, the potatoes should be handled carefully so that there may be no damage to outer peel through cutting, bruising and cracking etc.

Suitable Farm Practices

  • Before harvesting the potato crop should be undergone efficient and suitable farm practices like earthing, irrigation, fertilization and pesticide application so that the tubers may achieve proper health and strengths before harvesting.

Sanitary Conditions In Storage

  • The storage walls, ceiling, filling boxes and equipment should be free from insects and disease organisms. The air circulation and water distribution should be free from contamination.

Environmental Conditions


  • The best storage temperature for potatoes are reported to be 40-45 deg F.
  • The lower and higher temperature cause some changes in cooking, processing and germination qualities, increase storage losses and also reduce storage life of potatoes.

At lower temperature below 40 deg F

  • The tubers start converting starch into sugars and tubers become sweet.
  • The peeled tubers turn brown and colour of chips become black
  • Seed potatoes become less affective for germination as their dormancy breaking capacity decreases rapidly
  • There is rapid loss of vitamin C
  • It causes infection of blight, blank heart mahogany diseases
  • The wound healing and skin hardening capacity decrease rapidly.

At high temperature above 60 deg F

  • The respiration rate increases while reduces storage life.
  • There is moisture loss and cause shrinkage, writhing and sponginess in tubers.
  • Cause sprouting which reduces storage life and quality of germination.


  • The best relative humidity for storage of potatoes is 80-85 per cent at which there occurs minimum shrinkage and best physiological processes can be maintained.
  • If relative humidity is lowered below 70%, the loss of moisture by transportation becomes faster than the loss of solids by respiration, while results in decrease in specific gravity and tubers become light and spongy.
  • The specific gravity is the index of eating and cooking quality of tubers.
  • The temperature and ventilation are the controlling agencies of humidity.
  • The control of humidity in storage poses problems of condensation on walls and ceiling.
  • The condensed moisture dripping on the tubers may cause rotting and other excessive losses.
  • When moisture is added to the storage atmosphere, all water droplets should completely vaporize into air before coming in contact with tubers.


  • Ventilation affects the quality of potatoes in storage because of its relation to temperature and humidity of the storage atmosphere.
  • Ventilation usually may imply the introduction of outside air or merely the circulation of air within the storage.
  • The introduction of outside air is frequently a quick means to change temperature and humidity in the storage with motor operated thermostatically controlled ventilation.
  • Ventilation usually tends to lower the relative humidity surrounding the tubers unless the incoming air or recirculated air reaches to saturation condition.
  • Storage operations should be aware of the influence of ventilation on the humidity in air surrounding the tubers as well as in providing a more uniformity desirable temperature.
  • Hence Ventilation can have a considerable effect on the quality of potatoes.
  • The optimum air velocity for storage Ventilation is about 250-300 ft / min


  • Tuber exposed to light either natural or artificial gradually develops chlorophyll and Solanine formation in their tissues and become green in colour.
  • The green tuber have bitter taste and slowly develop undesirable quality due to green colour.
  • If the tubers are exposed to light a continuously long period, photosynthesis occurs frequently which brings some physio-chemical changes in the tubers. and hence affects the chemical composition of tubers.
  • The transportation losses of moisture also occur rapidly in presence of light.
  • Photeolytic enzymes become active during light and cause early ripening of tubers.
  • Further activity of these enzymes may cause rotting of tubers.


Five basic requirements for safe storage of potatoes

  • To provide satisfactory environmental conditions
  • To control disease causing organisms, enzymes and insects
  • To control sprouting in tubers during storage
  • To maintain potato firmness to prevent black spot
  • Gupta, R.R. 1978. Evaluation of storage characteristics of potatoes with evaporative cooling system.
  • Master of technology PAU Ludhiana thesis.
  • In Punjab, Seed tubers are stored in bags in cold stores at 4 deg-5 deg C and 90-95% relative humidity.
  • The seed material should be kept in cold store by 15 March as the delay affects the productivity of seed tubers.
  • High temperature leads to increased rate of respiration and water loss in tubers which affect their metabolic balance during storage.
  • Compared to ordinary store, the weight losses and rotting of tubers are negligible in cold stores.
  • Tubers moth, which is a serious problem before the advent of cold stores, has almost disappeared.
  • The only disadvantage of cold storage is that the leaf-roll virus is preserved with the seed tubers at low temperature.


Storage Design

  • Scientifically the most suitable shape is a sphere but the most practical shape is cube. The economical shape depends on the balance in cost between two opposing factors, viz., (a) narrower span reduces cost and (b) the shortest length of walls is provided by square shaped building.
  • Increase in height of building, as much as possible, reduces cost per unit material stored
  • Exterior surfaces should be protected against wind and rain. They must be water proof but not impermeable to the passage of water vapour from inside. Oil tempered hard wood is resistant to moisture and could be used as cladding material for both external and internal applications.
  • Solar radiation falling on internal surface may raise its temperature as much as 15.6 deg C above that of the atmosphere. Part of the heat is dissipated but part is transmitted through walls and roof. Heat gains through walls at 20 deg N latitude are lower on the south than on the east and west. South-East and South- West orientation occupies intermediate position. Heat gains through roofs are the lowest in the case of plaster ceiling with roof space alone, provided with tiles on board and felt.
  • Good insulation is important not only for refrigerated types of stores but also with the others where ventilation with the outside air is the only means of controlling store temperature. Extruded expanded polystyrene appears to be most suitable insulation material as it can be used without a vapour barrier which is essential with other materials such as insulation boards, glass fiber that absorbs moisture affecting their insulating property. Strawbale is considered expensive as it has the shorter life as compared with commercial insulants.
  • High relative humidity in stores reduces evaporation losses from potatoes but may lead to condensation on inside faces of walls and roofs. This can be avoided by a surface covering of straw to absorb condensation unless better insulation keeps up air temperature in the store roof space above or store air is recirculated whenever necessary.
  • Ventilation is necessary to dissipate the metabolic heat produced by potatoes through respiration. In an unventilated store, temperature may increase by 2 deg C / m storage depth.

The amount of ventilation and fan capacity can be calculated on the basis of 4 factors

  • Average outside temperature and its range.
  • Heat gains from potato respiration
  • Solar radiation and thermal transmittance of the building.
  • Heat gains from equipment.


Cooling Systems and Equipment

  • Duncan (1955) designed an evaporative cooling system using spray water as cooling agent.
  • A pump recirculates water at a rate greatly in excess of the evaporation.

The essential requirements for better operation of this system are as under

  • Uniform distribution of air across the spray chamber.
  • Suitable air velocity of about 300-700 fpm in washer chamber
  • An adequate amount of spray water broken into fine droplets
  • Good spray distribution across the air stream
  • Sufficient length of travel through the spray and wetted surfaces
  • Elimination of free moisture from the outgoing air.
  • Wilson (1971) designed a forced evaporative humidifier. He concluded that the rate of evaporation of water is limited by the following factors:
  • Water surface area exposed to air
  • Rate of air flow in the chamber
  • Mixing motion of air with water
  • Temperature of water in circulation.
  • Fergin (1974) studied various combinations of heat recovery and evaporative cooling.
  • In a simple evaporative cooling system, Outside air is cooled by water spray to the desired supply air conditions.
  • The second part consists of spray nozzles or cooling pads. Entering that side, air is cooled by water spray.
  • The cooled air then absorbs heat from a second outside air stream via heat recovery unit.
  • This second air stream is then further cooled by a second water spray and then introduced into the control chamber.
  • Subramanium (1970) studied about of thermal insulation for cold stores.
  • He used different insulation materials of different thickness for comparative performance.
  • He recommended paddy husk for walls and rock wool or thermocol for ceiling and other parts of the storage structure for better performance.


Uses of Potatoes in Indian Kitchens

  • Potato is used in Indian kitchens in one way or the other and no meal is considered perfect without potatoes.
  • It is mixed in large number of dishes and hoped that these dishes whether exclusively potatoes or not, will form either a part of the basic diet or shall be used for special occasions, etc.

  • Item
    Ingredients Remarks
    Potato-Cheese crispies Medium sized
    cooked potato,
    Butter, Mint,
    Craft cheese
    Grate boiled potatoes
    Beast in the butter when cold.
    Chopped craft cheese and a little mint coriander chutney
    Shape the mixture into small balls, toss them lightly and fresh breadcrumb and deep-fry them in ghee oil until golden brown.
    Potato Cheese Splits Medium
    or Craft
    sauce or Mango
    Bake the washed potatoes until they feel soft when pinched or forked. Split each potato into halves, place a cheese slice, little chutney and ½ teaspoonful (2-3 g) butter or as per taste.
    Banana Split Banana per
    cream to
    decorate the
    / Apricot or
    any Jam
    Peel bananas. Brush with a thick coating of the jam. Coat with potato crisps. Pipe cream on each banana in a simple line. Serve immediately.
    Potato Straws Large
    WaterOil or
    Ghee for frying
    Peel and cut potatoes into very thin long strips. Immerse them in a solution of ice water and salt for about ½ hour. Drain and dry them on a piece of cloth. Heat oil and deep-fry the potato straws until crisp and golden brown. Serve them sprinkled in the salt and pepper as per taste
    Potato Crisp Praline Potato
    Heat sugar in a small thick pan, unless melted continue to heat until goes golden brown on very low heat. Crush the wafers with Belan and quickly stir into the sugar and pour at once in a thin layer over a greased baking sheet or Thali. Leave to set. Crush it when dry. Store in airtight jar until required.
    Potato-Rice Hamburger Boiled
    Combine potato with salt & pepper
    Form a potato partly covered with mashed cooked rice to form flat balls
    Role in fine bread crumbs and fry.
    Potato Balls Boiled
    bread slicesSalt
    Anardana etc.
    Mesh potatoes
    Soften the bread (after removing their all 4 crusts) in water and press them within palms to drain off excess water
    Mix this bread with potatoes and the herbal powder
    Make into patties of heart, leaf or any other shape
    Deep fry in extra hot medium.
    Potato Soup Potatoes
    Cream Or
    Parsley Or
    And Pepper
    Peel and wash potato and other vegetables
    Cut potatoes and carrot into small pieces
    Boil in ½ liter water until soft
    Strain and put them into a pan
    Add other vegetables, 400 ml water and boil once
    In another frying pan, Saute onions in butter until brown
    Add the flour and saute again
    Mix cooked ingredients in a pan, Pepper to taste, mix curd, sprinkle with garam Masala and chopped parsley and serve hot.
    Potato or Crunchy Omelet Egg per
    person Course
    chopped potato
    Wafers or
    & SaltGhee
    Beat well the eggs
    Mix with pepper and salt
    Heat the oil in a 8-10" pan and cover the base with thin layer of crushed wafers or grated potatoes
    Pour over the egg mixture, stir very lightly cook until golden brown and serve.
    Baked Potatoes Large
    per person
    Salt, Pepper
    Wash and dry the potatoes
    Wrap in aluminum foil to be baked with hot coal or burnt cows dung or hot oven at 350 deg F.
    Pierce the fork while cooking to let the steam out
    Peel and serve with salt, butter, and sauce
    Use small potatoes for quicker cooking.
    Potato Salad Medium sized
    chillies chopped
    & vinegar
    lightly cover
    the salad
    Peel , slice and boil potatoes until just cooked
    Do not overcook otherwise they will break
    Drain and mix potatoes with remaining ingredients except mayonnaise and chillies
    Add mayonnaise just before serving
    Garnish it with shaved carrot, coriander leaves or cabbage or chopped tomato.
    For oil and vinegar dressing: mix 2 tablespoonful salad oil and 1 tablespoonful vinegar, 1 spoonful salt + 2 spoonfuls freshly ground pepper and shake well.
    Potato Pan Cakes Potato
    Sauce or
    Wash, peel and finely grate potatoes in salted water
    Slieve grated potatoes
    Mix grated potatoes with onion in a bowl
    Add beaten eggs and mix well.
    Make into thick cake and fry until brown on both sides.
    Serve hot with chutney
    Potato charchari Medium
    red chillies
    halved, Turmeric powder, Water,
    Lime juice
    Peel and cut potatoes after washing potatoes.
    Fry the poppy paste in same in the same oil after frying potatoes
    Add potatoes, salt, turmeric, chilli powder and fry 1-2 minutes.
    Add water, cover and simmer till potatoes are tender and water absorbed
    Add lime juice and serve hot.

Crispy Tips to Instantly Add the Potato Flavour

  • Replace French fries with the wafers. Crumble the wafers on scrambled eggs or panion bhurji or salads for better taste.
  • Enhance flavour of thick soups with a topping of broken potato crisps.
  • Finally crushed potatoes are a better substitute for bread crumbs for the pakoras / bondas, etc.
  • Add crunchiness of potato by layering broken potato wafers between butter and / or vegetables in the bread sandwiches.
  • Plain cakes taste and look better if a mixture of chopped wafers and sugar is put on the top of plain cake before baking.