Potatoes [German version]

Table of contents

General:
Product information
Packaging
Transport
  Container transport
  Cargo securing


Risk factors and loss prevention:
Temperature Odor
Humidity/Moisture Contamination
Ventilation Mechanical influences
Biotic activity Toxicity / Hazards to health
Gases Shrinkage/Shortage
Self-heating / Spontaneous combustion Insect infestation / Diseases




Product information

Product name

German Kartoffeln
English Potatoes
French Pommes de terre
Spanish Patatas
Scientific Solanum tuberosum
CN/HS number * 0701 ff.


(* EU Combined Nomenclature/Harmonized System)



Product description

The potato belongs to the nightshade family (Solanaceae). It is originally a native of South America (Peruvian-Bolivian Andes and coastal areas) and was known there by AD 200, arriving in Europe in the 16th century. Because of their similarity in appearance to truffles, the Italians named them tartufoli, from which their German name "Kartoffeln" is derived.

Potatoes are the starch-rich tubers of the underground stems (stolons) of Solanum tuberosum, serving to store nutrients for the parent plant.

The following criteria are used in dividing potatoes into their various varieties:

type of use: table, processing and seed potatoes
time of harvest: very early varieties (for immediate consumption), early varieties (suitable for potato salads, since not very mealy), medium early varieties (for cellar storage), medium late and very late varieties (of which some are good table potatoes for cellar storage and some are fodder and processing potatoes, since they are often very mealy)
tuber shape: round, oval, long, long oval or kidney-shaped
color of flesh: yellow or white
color of skin: light yellow, ochre-colored to red
skin texture: rough-skinned, smooth-skinned


Early potatoes are loose-skinned, i.e. they have a thin skin which flakes off easily, causing them to spoil easily.

Mid and late varieties are firm-skinned and therefore more resistant.

Peeled potatoes are composed as follows:

16 - 18% starch
75 - 78% water
2% protein
1% minerals
1% cellulose


Quality / Duration of storage

On loading, potatoes must be

fully mature (sprout dormancy stage) and firm-skinned,
undamaged, sound and of a single variety,
not green, wet or smeared,
free from soil (rot pathogen), organic constituents and stones (otherwise there is insufficient space for airing between the tubers).


It is also necessary to establish that the potatoes have been stored for a specific period postharvest (drying and wound healing period) and are not being loaded while still moist from the soil.

Postharvest, a distinction is drawn between three periods:

drying period (1 - 2 days postharvest):

The tubers must be dried immediately postharvest, to deprive rot pathogens of suitable living conditions and to provide favorable conditions for the subsequent wound healing period. If drying is delayed by just 24 hours, a question mark must be put over its effectiveness. Drying (in the case of storage in heaps) must be performed using the largest possible quantity of air (50 - 100 m3/h) at temperatures 2 - 3°C below stack temperature, although the temperature of the potatoes must not fall below 8°C. If the tubers are covered in a film of water, oxygen depletion occurs, resulting in the risk of rapid rotting. If freshly-harvested potatoes are put into storage straight from the field, they must initially be ventilated continuously for 36 hours, to dry them.

wound healing period (10 - 14 days postharvest):

Injured areas are protected from the penetration of rot-inducing microorganisms by suberization, for which purpose temperatures of 12 - 16°C and relative humidities of 85 - 95% must be ensured. In the event of oxygen depletion and a CO2 content > 0.5%, respiration and thus wound healing are suppressed and the onset of rot is encouraged.

Given the tried and tested method of drying with cooler air than that present in the potato stack and so as to prevent premature sprouting, it is more advisable to allow the wound healing period to proceed at temperatures of 8 - 14°C.

If temperatures are too cool (< 8°C) and the air is too dry, immature, loose-skinned tubers will transpire excessively due to the high permeability of their skin. In the first month after harvest, weight loss (=water loss through transpiration) may amount to 4 - 6%; the tubers become soft and have a greater tendency to blue spots and Fusarium dry rot.

Mature, firm-skinned tubers exhibit only 1 - 3% weight loss due to transpiration.

If potatoes are loaded during the wound healing period, the climatic conditions typical of this period must be taken into account.

Cooling/chilling period:

Where the temperature is low, the potatoes may heat up by approx. ¼°C per day due to the respiration process. To keep respiration and transpiration losses as low as possible, temperatures of 4 - 6°C and relative humidities of 90 - 95% are deemed best for this period. The reduction in temperature down to the travel temperature must proceed gradually and by no more than 0.5 - 1.0°C/d.


The above-mentioned stages must be taken into account when selecting the travel temperature.

Maximum duration of storage is as follows:

Temperature Rel. humidity Max. duration of storage Source
4 - 6°C 90% 10 months [5]


The storage and transport duration of potatoes cannot be notably affected by using controlled atmosphere transport.


Intended use

Potatoes are a staple food (table potatoes), but may be processed, for example into French fries.

High-starch, mealy potatoes are best suited to stews, while firm, low-starch varieties are suitable for making home fries and potato salads, for example.

Processing potatoes are used, among other things, to produce starch, alcohol and protein.


Figures

(Click on the individual Figures to enlarge them.)

Drawing, potato

Figure 1


Figure 2



Countries of origin

This Table shows only a selection of the most important countries of origin and should not be thought of as exhaustive.

Europe Germany, France, Greece, Great Britain, Israel, Italy, Netherlands, Poland, Portugal, Romania, Russia, Spain, Turkey, Cyprus
Africa Egypt, Morocco
Asia China
America USA, Cuba
Australia  


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Packaging

Potatoes are mainly transported in wide-meshed bags, but are sometimes also transported in perforated plastic bags, crates, cartons and baskets.


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Transport

Symbols

Symbol, general cargo

General cargo
Symbol, temperature-controlled

Temperature-controlled



Means of transport

Ship, truck, railroad, aircraft


Container transport

Actively ventilated containers, open-sided containers, flatracks (for loading below deck)


Cargo handling

In damp weather (rain, snow), the cargo must be protected from moisture, as there is otherwise a risk of premature spoilage.

Their high water content also makes them particularly sensitive to bruising and they must therefore be handled with care.

The required refrigeration temperature should be maintained, even during cargo handling.


Stowage factor

1.95 - 2.03 m3/t (jute fabric bags, 25 kg) [1]
1.53 - 1.81 m3/t (bags) [11]
1.62 - 1.90 m3/t (cartons) [11]
1.70 - 2.25 m3/t (bags) [14]
1.98 - 2.25 m3/t (cartons) [14]
1.62 - 1.90 m3/t (corrugated board cartons) [14]
1.53 - 1.67 m3/t (bulk cargo) [14]


Stowage space requirements

Cool, dry, good ventilation, as dark as possible


Segregation

Matting, jute coverings, fiber rope, thin fiber nets


Cargo securing

In the case of potatoes loaded in bags, stack heights of up to eight bags are desirable where possible (maximum stack height: 12 - 13 bags), to ensure adequate airing of the cargo block. For this reason, "ventilation trenches" should also be provided, which must be protected from possible blockage by slipping bags.

If the potatoes are loaded in boxes or cartons, these must be arranged in such a way that spaces between packages or pallets are filled, to prevent slippage or tipping. By selecting the correct packaging size or cargo unit (area module or area module multiple), holds can be tightly loaded (without spaces).


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Risk factors and loss prevention

RF Temperature

Potatoes require particular temperature, humidity/moisture and ventilation conditions (SC VII) (storage climate conditions).

A written cooling order must be obtained from the consignor before loading is begun. This order must always be complied with during the entire transport chain.

The following Table merely constitutes a rough estimate of appropriate temperature ranges. Temperatures may deviate from these values, depending on the particular transport conditions.

Designation Temperature range Source
Travel temperature 4 - 12°C [1]
4 - 6°C [2]
4 - 12°C [4]
4 - 6°C [5]


Transport temperatures must be such that, on the one hand, respiration losses and thus in particular weight losses due to evaporation are kept as low as possible and, on the other hand, the tubers do not become sweet.

The respiration intensity of potatoes is at a minimum between 3 - 5°C, and from 12 - 18°C increases two- to three-fold for every 10°C, subsiding at 40 - 50°C with increasing damage to the tuber. The critical temperatures are between 21 and 29°C.

As sprout dormancy subsides, the potatoes may start to sprout if temperatures are > 6 - 7°C. Therefore, before the cargo is accepted, it is important to find out whether the potatoes underwent intermediate storage at the charterer's or consignor's premises and under what the storage conditions, since this question is of importance in relation to the duration of sprout dormancy. If the storage temperature was over 6 - 7°C, the onset of sprouting must be expected.

At temperatures < 3°C, potatoes start to become sweet and to lose their flavor (chilling damage). At -2 to -3°C they freeze. Short-term chilling during cargo handling at temperatures even as low as -2°C may be tolerated; however, frost-damaged potatoes must be rejected.

Elevated heat and moisture levels, on the other hand, encourage rotting and sprouting. Thus, temperatures > 12°C result in an increase in respiration intensity and at temperatures of around 40°C the tuber is damaged.


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RF Humidity/Moisture

Potatoes require particular temperature, humidity/moisture and ventilation conditions (SC VII) (storage climate conditions).

Designation Humidity/water content Source
Relative humidity 85% [1]
85 - 90% [2]
Water content 75 - 78% [1]
Maximum equilibrium moisture content 80% [1]


When the potatoes are delivered for loading, it must be ensured that no damp bags or boxes are accepted. Any wetting damage or areas of rot must be removed at source, to prevent them from spreading. In damp weather (rain, snow), the cargo must be protected from moisture, since moisture may lead to mold growth and premature spoilage.

Droplet formation on the ceiling of the hold and layers of condensation in the upper part of the potato stack provide the best possible living conditions for potential rot pathogens. Excessively damp, warm storage causes roots to form at the bottoms of the sprouts. These grow together and become matted, so making it difficult subsequently to separate the tubers. Large-scale weight and nutrient losses then occur.

Potatoes must not come into contact with salts, since these absorb water vapor as a result of their hygroscopicity.


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RF Ventilation

Potatoes require particular temperature, humidity/moisture and ventilation conditions (SC VII) (storage climate conditions).

Recommended ventilation conditions: 60 - 80 air circulations/hour (air exchange with continuous supply of fresh air).

Potatoes are best transported at an oxygen content of 16 - 18% and a carbon dioxide content of 2 - 3%. Oxygen supply must be ensured by active ventilation, since a shortage of oxygen (O2 content of hold air < 6 vol.%) leads to the onset of anaerobic respiration and fermentation.

Since potatoes make heavy demands of the ventilation system, it is recommended, in the case of conventional loading, to keep stack heights to eight bags where possible (maximum stack height: 12 - 13 bags), so as to be able to ensure adequate airing of the cargo block. For this reason, "ventilation trenches" should also be provided, which must be protected from possible blockage by slipping bags.


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RF Biotic activity

Potatoes display 2nd order biotic activity.

They are living organs in which respiration processes predominate, because their supply of new nutrients has been cut off by separation from the parent plant.

Care of the cargo during the voyage must be aimed at controlling respiration processes (release of CO2, water vapor, ethylene and heat) in such a way that the cargo is at the desired stage of ripeness on reaching its destination. Inadequate ventilation may result in fermentation and rotting of the cargo as a result of increased CO2 levels and inadequate supply of atmospheric oxygen (see Ventilation).

Potatoes must also be protected from light (daylight, sunlight and even artificial light in the hold), since light on the one hand causes the activation of growth-promoting enzymes (=> sprouting), resulting in nutrient loss and thus quality degradation (consistency, flavor), and on the other hand causes the tubers to turn green, which may give the potatoes an unpleasant, bitter taste due to an increase in solanine (see RF Toxicity/Hazards to health), present in particular at the stolon end of the tuber.


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RF Gases

CO2 evolution during sprout dormancy of the potatoes (relative in each case to 100g fresh weight):

at 5 - 10°C: 0.8 - 1.4 mg/h

at 20°C: 2.0 - 4.0 mg/h
Upper limit of permissible CO2 content 0.5 vol.%.
Ethylene evolution  
Active behavior The rate of ethylene production is very low, being below 0.1 µl/kg*h [16].
Passive behavior Potatoes are moderately sensitive to ethylene [16]. The effect of ethylene is to cause the premature onset of the sprouting process. Thus, products which release large quantities of ethylene (e.g. apples) cause potatoes to sprout prematurely (allelopathy). For this reason, potatoes should not be stowed together with products which produce large amounts of ethylene, e.g. citrus or pomaceous fruit, since the entire cargo may be lost.


If ventilation has been inadequate (frost) or has failed owing to a defect, life-threatening CO2 concentrations or O2 shortages may arise. Therefore, before anybody enters the hold, it must be ventilated and a gas measurement carried out.


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RF Self-heating / Spontaneous combustion

No risk.


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RF Odor

Active behavior Potatoes emit a characteristic, strong, slightly unpleasant odor.
Passive behavior Potatoes are highly odor-sensitive and readily absorb foreign odors, e.g. gasoline, kerosene, chemicals and foodstuffs with a strong odor.



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RF Contamination

Active behavior Potatoes produce dust.
Passive behavior Potatoes are sensitive to dirt, fats and oils.



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RF Mechanical influences

Potatoes are sensitive to mechanical stresses. Care should be taken to ensure that the potatoes have been held in storage for at least the so-called wound healing period (10 - 14 days postharvest) prior to transport, so that any injuries caused to the tubers during harvest may have healed and no rot phenomena will occur during transport.


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RF Toxicity / Hazards to health

If ventilation has been inadequate (frost) or has failed owing to a defect, life-threatening CO2 concentrations or O2 shortages may arise. Therefore, before anybody enters the hold, it must be ventilated and a gas measurement carried out. The TLV for CO2 concentration is 0.49 vol.%.

Potatoes exposed to sunlight or artificial light turn green, particularly in eye areas, due to the toxic alkaloid solanine. In cultivated varieties, the green discoloration does not cause any real harm to health; however, green areas taste bitter and must be cut out.


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RF Shrinkage/Shortage

Over relatively long transport periods, potatoes may lose up to 10 - 15% in weight due to respiration processes and water vapor release. This loss is accompanied by a reduction in nutrient and vitamin content as well as impaired consistency and a reduction in the proportion of aroma substances in the tuber.


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RF Insect infestation / Diseases

Because of their high water content in particular, potatoes have a tendency towards large losses caused by various factors:

Mechanical damage includes torn, chopped, squashed or cut tubers, which are classified as mechanically damaged if the damage extends to more than 5 mm below the surface. Very loose-skinned potatoes also fall into this category, if over 25% of their skin is missing or loose.
Animal damage is caused when potatoes are eaten by worms, snails and mice. On board an ocean-going vessel, there is a particular risk of the introduction of rats and mice. For this reason, increased attention should be paid to nibbled tubers and to rat and mouse droppings.
Freezing injury: the tuber skin can be easily detached and the damaged tissue parts become watery and soft. After a relatively long period of chilling, the tuber flesh displays a dark marbled effect when cut open.
Damage due to chemicals: if potatoes come into contact with fertilizing salts or other corrosive chemicals, the skin and tuber flesh are destroyed by the corrosive action of these chemicals.


The best known potato rots, caused by temperatures > 20°C, high humidity and inadequate air circulation, are:

tuber rot or late blight: this is a fungal disease caused by the fungus Phytophthora infestans and may be recognized from the lead-gray, sunken spots of indeterminate shape which cover the tuber surface and extend into the tuber flesh as brown to red areas which are unclearly defined relative to the healthy tissue. Late blight may spread very extensively in only a few days. It is often not clearly detectable at the time of sampling, but may assume considerable dimensions during maritime transport. Additional bacteria frequently penetrate through the affected tissue, causing so-called wet rot, which has no common origin with late blight.
Wet rot: wet rot is caused by bacteria (Pectobacterium carotovorum), which penetrate the flesh of damp or damaged potatoes, often through small cracks, and turn it mushy. Often, some of a tuber suffering from wet rot is still firm, while the rest is brown and soft. The disease may spread through an entire cargo within just a few weeks. The bacteria either attach themselves to a damaged tuber or have already attacked the tuber previously during growth through black-leg stems. This tuber wet rot may have devastating consequences. The disease is suppressed by cool, dry stowage and regular ventilation. Potatoes suffering from wet rot crush easily in the hand: all that is required is finger pressure on the affected point, the mushy mess which is discharged being the characteristic feature of wet rot. Diseased tubers are often squashed by the pressure of potatoes lying on top, allowing the bacteria to go on to infect healthy potatoes. This makes wet rot difficult to suppress, and it frequently leads to loss of the entire cargo.
dry rot: discernible from sunken points and staining.
white mold: discernible from a white, fluffy mealy deposit on the tuber surface.
heart rot: determinable from the cavities inside the tuber.


Quarantinable diseases are:

potato wart: determinable from the cauliflower-like outgrowths.
ring rot, fungal ring rot, bacterial ring rot: characterized by discoloration of the vascular ring.
powdery scab: rough corky unevennesses on the skin surface.
potato moth


The following conclusions can be drawn from the appearance of the potatoes during the unloading process or from changes in the atmospheric environment:

soft, black potatoes are caused by inadequate ventilation.
chilling is recognized by black coloration beneath the potato skin.
a rapid increase in temperature is caused by the more intense respiration of diseased tubers and indicates the presence of seats of rot which must be removed immediately.
if the temperature of the cargo increases excessively, only forced ventilation can save the cargo from overheating and thus rapid decay.
greening of the tubers indicates that they have been exposed to strong sunlight or artificial light during storage ashore or on board (particularly on ro-ro ships).


The quarantine regulations of the country of destination must be complied with and a phytosanitary certificate and fumigation certificate may have to be enclosed with the shipping documents. Information may be obtained from the phytosanitary authorities of the countries concerned.


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