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.

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.