Walnuts [German version]

Table of contents

Product information
  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 Walnüsse
English Walnuts
French Noix
Spanish Nuéz
Scientific Juglans regia
CN/HS number * 0802 30 ff.

(* EU Combined Nomenclature/Harmonized System)

Product description

Walnuts are the rounded, single-seeded stone fruits of the walnut tree native to southern Europe, which is a member of Juglandaceae family. The walnut is enclosed in a green, leathery, fleshy husk which is inedible. Removal of the husk reveals the wrinkly walnut shell, which is in two halves, and encloses the kernel, which is likewise in two halves separated by a partition (see Figures 2 and 3). The seed kernels are enclosed in a brown seed coat which contains antioxidants. The antioxidants protect the oil-rich seed from atmospheric oxygen so preventing rancidity (oxidative rancidity).

Walnuts are shell fruit (nut types). Because of their similar characteristics with regard to transport, particularly their high oil content, their requirements regarding care during storage and transport are the same as those of oil-bearing seeds/fruits.

Due to their high fat content, walnuts have a significant nutritional value. They are of the following composition [2]:

water: 5%
protein: 15%
fat: 63%
carbohydrates: 13%
fiber: 2%
minerals: 2%

Oil content:

50 – 65% [1]
40 – 65% [3]

Quality / Duration of storage

Characteristic indicators of good quality are: large seeds (nuts), thin shell, pleasant flavor (not rancid) and a light shell color. On acceptance, particular attention must be paid to inspecting the cargo for insect infestation.

The nut shells may also become unattractive due to tannin which makes black stains on the outer shell in particular. For this reason, walnuts are sulfur-treated and, now, are bleached only with sodium hypochlorite.

According to [3], walnuts must be neither rancid nor moldy and at most 10 – 15% may be empty (10% of empty walnuts is considered normal).

It is very important for the surveyor to ascertain the year of harvest: it must be taken into consideration that the nuts may be mixed with nuts from the previous year’s harvest. This possibility must not be disregarded when determining whether or not loss has occurred in transit. Nuts from the previous year’s harvest have a tendency to beetle infestation and rancidity.

According to [5], dried walnuts may be kept for up to 12 months at temperatures of -3 – 0°C, while fresh walnuts may only be kept for a very short time.

Intended use

Walnuts are primarily eaten raw and are also used in trail mixes. Walnuts are also processed into walnut paste for the confectionery and bakery industries. Walnut oil is obtained by pressing fully ripened walnuts; this oil is ideal for salad dressings.


(Click on the individual Figures to enlarge them.)

Drawing, walnuts

Figure 1
Photo, walnuts

Figure 2
Photo, walnuts

Figure 3
Photo, walnut

Figure 4
Photo, walnuts

Figure 5

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 Italy, France, former Yugoslavia, Turkey, Romania, Bulgaria
Asia China, India
America Chile, USA (California)

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Walnuts are packaged in, among other things, net bags (1.5 – 2.5 kg), polysacks (5 and 10 kg), cartons (10 kg) and flat jute fabric bags (55 kg).

Shelled nuts are packaged in, among other things, boxes lined with parchment paper, each containing 12.5 kg (net).

Walnut kernels are ideally stored at a water content of 2 – 3% in packaging which is impermeable to water vapor. Vacuum packaging excludes atmospheric oxygen, which promotes rancidity.

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Symbol, general cargo

General cargo


Means of transport

Ship, railroad, truck, aircraft

Container transport

Ventilated containers (coffee containers), if the lower limits set for the water content of goods, packaging and flooring and the oil content of the goods are complied with and if protection against solar radiation is ensured (risk of self-heating).

Cargo handling

In damp weather (rain, snow), the cargo must be protected from moisture, since it may lead to mold, spoilage and self-heating as a result of increased respiratory activity.

No hooks should be used with bagged cargo, so as to prevent damage to the bags and loss of volume.

Stowage factor

2.10 m3/t (flat jute fabric bags, 55 kg) [1]

Stowage space requirements

Cool, dry, good ventilation


Fiber rope, thin fiber nets

Cargo securing

In order to ensure safe transport, the bags/cartons must be stowed and secured in the means of transport in such a manner that they cannot slip or shift during transport. Attention must also be paid to stowage patterns which may be required as a result of special considerations, such as ventilation measures.

In the event of loading as general cargo, dunnage should be used to protect against damage:

Floor dunnage: criss-cross dunnage and packing paper
Side dunnage: lining with wooden dunnage and mats or jute coverings: protection from metal parts of the ship, since traces of metal promote cargo rancidity due to autoxidation.
Top dunnage: important for voyages to cold regions (winter), since sweat may drip onto the cargo.

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Risk factors and loss prevention

RF Temperature

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

For this reason, precise details should always be obtained from the consignor as to the travel temperature to be maintained.

Designation Temperature range Source
Favorable travel temperature range 5 – 25°C [1]
-3 – 0°C [5]

The stated temperature range of -3 – 0°C is the ideal temperature for achieving the longest possible storage life, but travel temperatures of 5 – 25°C are feasible, depending upon the duration of the voyage, so this product need not necessarily be carried as chilled goods. It must, however, be borne in mind that the storage life of the product is correspondingly reduced at temperatures higher than the above ideal temperature.

Temperatures > 30°C must not prevail for a long period, as respiration of the cargo is otherwise promoted.

Walnuts should not be stowed near heat sources (engine room bulkhead, heated tanks).

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RF Humidity/Moisture

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

Designation Humidity/water content Source
Relative humidity 70% [1]
Water content 2 – 8% [1]
5% [2]
5 – 7% [3]
4 – 5% [5]
Maximum equilibrium moisture content 65% [1]

Precise details should be obtained from the consignor as to the relative humidity to be maintained during the voyage.

Moisture damage to both unshelled and shelled walnuts occurs under particularly unfavorable conditions, such as direct contact with rain or by dripping cargo sweat, if the product has not been protected by wooden dunnage, mats or jute coverings. Such protection is also important in order to minimize the risk of rancidity due to contact between the nuts and metal parts of the ship’s hull or of the container.

Nuts which have been wettened by rain may only be accepted once fully dried.

Walnuts have the best color and flavor when their water content is 2 – 8%. A higher water content reduces storage life and increases the risk of rancidity.

As is evident from the sorption isotherm for walnuts, these water contents are at equilibrium with comparatively low relative humidities of up to 73%, i.e. below the mold growth threshold of 75%. However, the sorption isotherm then rises sharply at higher values, e.g. at 75% relative humidity, the water content of the walnuts has risen to 14%.

Sorption isotherm

Figure 6

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RF Ventilation

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

Recommended ventilation conditions: air exchange rate: at least 10 changes/hour (airing)

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RF Biotic activity

Walnuts 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 keeping decomposition processes at the lowest possible level, so as to keep within limits any losses in quality caused by the emission of CO2, heat and water vapor.

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RF Gases

In walnuts (particularly when fresh), metabolic processes continue even after harvesting. They absorb oxygen and excrete carbon dioxide (CO2).

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.%.

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RF Self-heating / Spontaneous combustion

Oil content:

50 – 65% [1]
40 – 65% [3]

Because of their tendency to self-heating, walnuts may behave like substances from Class 4.2 of the IMDG Code.

Heating damage occurs in particular in shipments from India, Chile and other tropical regions due to incorrect stacking before and during the voyage and results in rancidity of the nuts, which will subsequently at best be suitable for industrial processing.

Walnuts should not be stowed together with fibers/fibrous materials as oil-soaked fibers may promote self-heating/spontaneous combustion of the cargo.

Fat decomposition in walnuts leads to the risk of self-heating and, ultimately, to a cargo fire.

Fat decomposition may proceed as follows:

by hydrolytic/enzymatic fat cleavage or
by oxidative fat cleavage

Hydrolytic/enzymatic fat cleavage:

If the critical water content of the walnuts is exceeded, this promotes hydrolytic/enzymatic fat cleavage. Fat-cleaving enzymes are activated by the elevated water content. The additional action of light and heat may accelerate this process. Free fatty acids sometimes have an unpleasant odor and taste. In the event of extended storage or improper cargo care, these cause the cargo to become rancid.

The free fatty acids formed are consumed by respiration processes in the walnuts to form carbon dioxide and water, a process which is associated with considerable evolution of heat.

Self-heating of walnuts is an extremely vigorous process, as the consumption of fatty acids by respiration processes is associated with a considerably greater evolution of heat than is the case with the respiration equation for carbohydrates. Here too, as with cereals, the spoilage process proceeds in a type of chain reaction, because heat and water are formed by the fatty acids consumed by respiration, which in turn contribute to an intensification of the process.

The self-heating of walnuts requires only a small seat of moisture, so that within just a few hours heating may occur at moist points for which weeks or months would be required in goods dry on shipment.

Fresh walnuts with a high water content tend in particular towards rapid self-heating and may also ignite. Self-heating of walnuts leads not only to a reduction in the utility value of this product (rancid odor and taste) but also has a qualitative and quantitative effect on oil yield. The color and bleachability of the oils are also negatively affected. The oil obtained complicates refining of the crude oils in subsequent processing, because a higher free fatty acid content makes decolorization substantially more difficult.

Hydrolytic/enzymatic fat cleavage and respiration may be limited by low temperatures; however, this may only be affected to a limited degree during transport. It is therefore important to ensure storage stability by complying with the limit values for the water content of the goods.

Oxidative fat cleavage:

Food components frequently react with atmospheric oxygen in spoilage processes. Atmospheric oxygen may enter into an addition reaction with unsaturated fatty acids through the simultaneous assistance of light, heat and certain fat companion substances, and possibly also traces of heavy metals. Rancidity caused by oxidative fat cleavage is particularly noticeable in the case of shelled walnuts, because the shelling process results to a certain degree in exposure to atmospheric oxygen or to the steel parts of the ship or the container walls, if not carefully covered. It is therefore absolutely essential to store walnuts in the dark and to protect them from oxygen and metal parts, since otherwise they become brown-colored and develop a rancid odor and taste.

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RF Odor

Active behavior Walnuts have a very slight, pleasant odor.
Passive behavior Walnuts are sensitive to unpleasant and/or pungent odors. They should be stored and transported in clean air away from foodstuffs with an intense odor.

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RF Contamination

Active behavior Risk of contamination of other goods by fats and oils.
Passive behavior Walnuts are sensitive to dust, dirt, fats and oils.

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RF Mechanical influences

Walnuts are impact- and pressure-sensitive.

If stack pressure is too high, the walnuts are crushed, so promoting self-heating. In addition, if the nuts are transported in jute bags, the oils accumulate in the fabric and accelerate the process.

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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.%.

Danger: walnuts may contain aflatoxin. The molds Aspergillus flavus and Aspergillus parasiticus produce the toxin aflatoxin, which may be present in the cargo as a result of an attack by the above-mentioned mold types (see risk factors Humidity/Moisture and Ventilation). In general, this is „country damage“, i.e. the toxin is already present in the walnuts at the time of harvesting. As a rule, aflatoxin is only found in individual walnuts. If batches intended as a human foodstuff are affected by this toxin, the product can no longer be approved for human consumption. Walnuts affected by aflatoxin cannot readily be distinguished from the other nuts in a batch. The toxin may be detected using UV light.

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RF Shrinkage/Shortage

Weight loss of up to 2% due to moisture loss is tolerated.

Loss of volume may be caused by tears in bags and by theft. The risk is increased by repeated cargo handling and extended storage.

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RF Insect infestation / Diseases

On acceptance, attention must be paid to inspecting the cargo for insect infestation. The time of infestation may be determined with some certainty by the stage of development of the pests, with infestation generally occurring in the country of origin.

The proportion of empty, bad or pest-infested walnuts should not exceed 15%.

Mites, cockroaches, sawtoothed grain beetles, flour beetles, meal moths, dried fruit moths and rats and mice may attack walnuts. Walnuts from the previous year’s harvest have a particular tendency to beetle infestation.

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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