Potatoes

Infobox on Potatoes
Example of Potatoes
Freshness facts
Optimum carrying temperature	4° C (seed potatoes) 7°C (table potatoes) 10°C (processing potatoes)
Highest freezing point	-0,8°C
Acceptable product temp. at loading into containers	Max. 2°C above carrying temperature
Optimum humidity	90% to 95%
Ventilation setting for containers	10 m3/hr
Storage life	2-6 months (seed potatoes) 2-12 months (table/processing potatoes)
Climacteric / non-climacteric	Non-climacteric
Ethylene production	Very low
Ethylene sensitivity	Medium
Modified / controlled atmosphere	-
Potential benefits	-
Availability
	On demand

Potatoes

Harvesting and handling

Potato is grown throughout the world in temperate zones, with planting in the Spring and harvest in the Fall. There are many skin colours (brown russet, white, red, pink, yellow) and flesh colours ( white, cream, yellow, blue/purple/red, and striated). Tuber shapes vary from round, oblate, oblong to long.

A high quality fresh-market potato tuber will be turgid, well shaped, uniform, brightly coloured (especially reds, whites and yellows), as well as free from adhering soil, mechanical damage, greening, sprouts, diseases, and physiological defects.

Cooling and storage

Long-term storage of potato tubers of up to 12 months requires that they be cured. Curing stimulates suberization, wound healing and reduces respiration. Optimal curing conditions are around 20°C with 80% to 100% RH and forced ventilation. Maintaining high RH is required at all times to minimize shrink and pressure bruising in storage.

Desired maintenance temperature depends on the desired end use of the tubers. Respiration rate of potato tubers is lowest at 2°C to 3°C. Storage at 0°C to 2°C increases the risk of freezing or chilling injury. Sprouting accelerates at temperatures >4°C to 5°C, so seed tubers are commonly stored at 4°C. Tubers for fresh consumption are stored at 7°C (to 10°C) to minimise conversion of non-reducing sugars such as starch to reducing sugars such as glucose, which darken during cooking.

Tubers for frying are stored at 10°C (to 15°C), depending on cultivar and it’s respective sugar conversion characteristics. Many chipping cultivars accumulate excessive sugar if stored <15°C. Thus, chipping cultivars are stored at 15°C to 20°C; new cultivars are being developed that will not accumulate sugar at temperatures as low as 5°C to 10°C.

Refrigerated carriage of potatoes has one potential hazard which is not always appreciated. If a cold cargo is discharged into a warm humid atmosphere, there is a grave risk of condensation followed by anaerobiosis, followed in due course by massive bacterial soft rot. It is therefore prudent (starting several days before arrival) to allow the cargo to warm to a temperature above the expected atmospheric dew-point. Even in the absence of condensation there remains a possibility of losses from bacterial soft rot if potatoes are held in warm, ill-ventilated conditions after discharge from the vessel.

Quality tubers can be stored for 2 to 12 months, depending on quality at harvest, quality of storage facilities, variety, and whether or not sprout inhibitors are used. Sprout inhibitor may be applied in the field before senescence begins, on the tubers as they are graded and packaged, or in the storage after curing is completed.

Freezing at -1°C, whether induced in the field or in storage, typically results in distinct demarkation between affected and unaffected tissue. Symptoms include a water-soaked appearance, glassiness, and tissue breakdown on thawing. Chilling injury can occur after a few weeks at 0°C and result in mahogany discolouration of internal tissue in some varieties. Much longer periods of storage are generally required for chilling injury to occur. Storage at 3°C to 4°C typically results in increased reducing sugar levels that are not reversible with re-conditioning.

See also: http://www.ukpandi.com/fileadmin/uploads/uk-pi/LP%20Documents/Carefully_to_Carry/Potatoes.pdf

Controlled atmosphere considerations

The usefulness of CA storage is minimal, and economic justification doubtful.

Storage disorders

Alternaria rot, Bacterial hard rot, Bacterial soft rot, Black heart, Black spot, Blight, Bruising, Chilling injury, Scab, Smut, Sprouting.

Additional information on potatoes

Additional information on overseas carriage of potatoes

In addition to the above information, the following aspects are of importance in the (long distance) carriage of potatoes:
Potatoes are commonly packed in bags made of Hussein, poly-mesh or kraft paper and also in crates, barrels and cartons.

Risks to be considered when planning stowage are:
Good ventilation is essential to avoid the build up of carbon dioxide which initially supports the sprouting process. Excess heat and moisture will cause sprouting and excess drying conditions causes evaporation and shrinkage. Over-exposure to strong sunlight may cause potatoes to become inedible.

DO NOT mix consumption/table potatoes with seed potatoes as this can contaminate the seed potatoes. (Seed potatoes should maintain a pedigree free of various crop infections and abnormalities).

Due regard should be given to not mixing different types/batches of table potatoes as it may cause cross infection.

Stowage can be provided as follows

Under active refrigeration

• In a 20 ft Open side
• In a 20 ft Fantainer
• In a 20 ft Ventilated Container
• In a 20 ft / 40 ft GP under special conditions
  
  

In Refrigerated 20 ft, 40 ft or 40 ft high cube integral reefers
Carriage temperature is approx. plus 7.5º C with air freshening of 30 m³/hr. The age of the crop will also dictate carriage as new potatoes tend to have a softer skin. Check with shipper on setting requirement. There may be a requirement to warm up the cargo prior to arrival by altering the set point.

In 20 ft Open sides
Must have their side curtains rolled up when in stow onboard ship in order to allow maximum ventilation. Must be stowed underdeck to prevent over-exposure to sunlight. Must be stowed in vessels which have mechanical underdeck ventilation providing a minimum of 14 air changes per hour. Open sides shall be arranged in underdeck stow to allow free air flow through the potato stow. Stowage next to deckhead girders which might obstruct air flow must be avoided and similarly anything that will hinder ventilation. If possible, avoid airflow across a series of container rows containing potatoes as this might transfer or cause cross infection The relevant ship's planner should be asked, in a Special Stowage Request, to stow underdeck for maximum ventilation. Opensides when stowed on the terminal must have their side curtains down during rain. Delivery at destination should be effected with the minimum of delay. Potatoes should spend minimum time in terminals from origin to destination.

In 20 ft Fantainers
Constant air circulation is provided by an extraction fan fitted on the left hand door of the container. Air is drawn through a vent on the front end of the container at floor level. Stow on deck protected from radiant heat. Ensure power supply is connected via control boards and tell tail ribbons attached to fan grills to indicate fan activity. Deliver cargo on arrival otherwise control boards to be landed and containers placed on power at the terminal.

In 20 ft Ventilated Containers (Sometimes referred to as Super Vents)
Ventilation is provided by convection through air ducts next to top and bottom side rails. Stow on deck protected from radiant heat and weather. Do not stow in the outrigger weather slots. Avoid long stays in terminals, particularly in freezing temperatures.

In 20 ft GPs
On very short transits (Rotterdam to Lisbon) certain crops can be carried without ventilation provided doors are cracked open on arrival at the destination terminal. Should be stowed on pallets to facilitate air circulation. A container fitted with passive vents should be selected to allow a degree of air circulation. May be carried at sea with a door lashed open (doors facing aft) for short transit voyages such as Port Said to Rotterdam. A pile weight restriction applies on top of a container with a door removed. May be carried with one door removed.

In 40 ft GPs
Similar to onions this has been done with a door removed and stowed in protected deck stow. It should be carefully weighed up before proceeding and is not the norm. The issues mentioned below should be borne in mind.

There is the danger of rain being driven into the container particularly in monsoon conditions. This could trigger mould and rotting. Air flow throughout a 40 ft container may be limited and this can be assisted by stowing on pallets. The condition and quality of the crop on loading is important.

Ensure the cargo is properly secured at the open doorway to prevent cargo falling out, particularly on road and rail transits. The latter will usually require special permission. Ensure road weight regulations are not breached.

General Note: Cargo temperature should stay as low as possible to the following limits. Seed potatoes : not lower than 4°-5°C; consumption potatoes : not lower than 7°C.

Table potatoes
Table potatoes are perishable and should be handled with care to avoid breaking and cracking. Should never be treated roughly and never loaded wet. Should not be stowed over eight tiers in height as to bottom tiers are liable to damage from over-stowing. This particularly applies to potatoes in bags or frail crates or cases.

Potatoes should be stowed in a cool, dry, well-ventilated hold at approx. 7°C. Potatoes are subject to damage by excess heat and moisture, which cause them to start sprouting, and excess drying conditions, which cause evaporation and shrinkage. It is, therefore, important that correct temperature and humidity are maintained by electrical ventilation, giving a minimum of 14 but preferably 16 changes per hour, to prevent the accumulation of carbon dioxide and to ensure a constant supply of fresh air. Sprouting can also be due to excess soil adhering to the potatoes but Phytosanitary Regulations of most importing countries put a very low limit on the amount of soil permitted in a bag and, consequently, this should not present a problem for properly dressed potatoes, which have been inspected prior to shipping.

A black, soft condition of the tubers may be evidence of poor ventilation in storage or stowage while a black discolouration just below the surface of the skin is probably evidence of freezing, in which case the tubers may show surface moisture. A green discolouration of the surface is indicative of over-exposure to strong sunlight after lifting or in storage or in transit. This causes potatoes to become inedible. As mentioned previously, potatoes are imported by most countries under strict Phytosanitary Regulations and it is important that they be maintained in the best condition possible so that the inspection authorities at the port of entry do not have to reject them due to mishandling in transit.

Seed Potatoes
The same rules apply to seed potatoes as to table potatoes and every care should be taken in handling them. Freezing or excess drying prevents the potatoes from sprouting and excess moisture causes the potatoes to grow long weak sprouts which are broken off in subsequent handling. Humid conditions encourage any bacterial and fungal diseases present to spread more rapidly through a sack, with subsequent damage to surrounding sacks. However, care must be exercised in differentiating between loss due to inherent vice and that caused by normal mishandling of sacks. This is of course, a matter for expert advice so as to avoid any subsequent controversy. The Plant Health Authorities in most countries can provide this service and they can, if necessary, call at short notice on experts in this field.

When shipping seed potatoes there are often a number of different varieties included in a cargo and it is important that any burst bags be refilled with care and that potatoes that have been spilt be rebagged quite separately. In both cases the bags should be marked accordingly, as it is very important that a farmer does not receive mixed varieties as each variety has its own characteristics, e.g., earliness, shape, colour, use, etc., which makes the subsequent crop if mixed, unacceptable to the consumer.