Wheat [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 Weizen
English Wheat
French Froment
Spanish Trigo
Scientific Triticum aestivum
CN/HS number * 1001 10 00

(* EU Combined Nomenclature/Harmonized System)

Product description

Wheat is a type of cereal belonging to the grass family (Gramineae), the term „cereals“ covering the grain fruits of cultivated grasses (spikes or ears in the case of wheat, rye, barley and corn; panicles in the case of oats and rice.

Today, wheat is the most important type of grain, with winter wheat being predominant.

The structure and chemical composition of the grain vary little between the different types of cereal. The cereal grain is a single-seeded indehiscent fruit, the husk of which is formed by the fusion of the fruit and seed walls. It consists of three components:

Its cracked husk, which gives the grain a greatly increased surface area relative to its mass. This allows the cereal grain to enter into an active exchange of materials with its environment.
the endosperm, which constitutes the main component of the grain.
the embryo.

After harvesting, wheat usually undergoes further post-ripening, which consists of the high molecular weight substances congregating further with water being expelled (syneresis). As the surface of the cereal then becomes damp because of the elevated water content, this is described as „sweating. In this state, the cereal is highly susceptible to mold and must not as yet be shipped. However, if the water content of the cereal is relatively low (approx. 13 – 14%), proper storage allows the sweat moisture to be absorbed by the air without the risk of mold growth. This sweating process proceeds for a period of approximately 1 – 2 months.

Grain size: diameter 2 mm, length 5 mm

Oil content: 1.9 – 2%

Quality / Duration of storage

Dull-looking batches of wheat indicate self-heating or excessive drying.

Checks should be carried out by an independent inspector and a certificate provided in relation to loading moisture content, the absence of odor and contamination and the absence of pests.

Wheat which is „dry for shipment“ (water content below 14%) may be kept for up to 12 months or longer provided that the appropriate temperature, humidity/moisture and ventilation conditions are complied with.

Intended use

Wheat is an ideal breadmaking cereal as it has a high gluten content. Wheat flour is also used to produce pasta products, while wheat is also used to make starch, Weizenbier (German wheat beer) and grain schnapps.


(Click on the individual Figures to enlarge them.)

Drawing, wheat

Figure 1
Drawing, wheat

Figure 2
Photo, wheat

Figure 3
Photo, wheat

Figure 4

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, Russia
Asia China, India
America USA, Canada, Argentina
Australia Australia

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Predominantly transported as bulk cargo, rarely in bags (seed in security sealed bags).

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Symbol, temperature-controlled

Bulk cargo
Symbol, general cargo

General cargo

Means of transport

Ship, railroad, truck

Container transport

Mainly in bulk containers, but also as bagged cargo (e.g. seed) in standard containers. Compliance with limits for the water content of the cargo and container floor must be ensured.

Cargo handling

In damp weather (rain, snow), the cargo must be protected from moisture, since wetting and extremely high relative humidities may lead to mold growth, spoilage and self-heating due to increased respiratory activity.

Suction and blowing devices may cause not inconsiderable damage to the grains.

Stowage factor

1.31 – 1.36 m3/t (bulk cargo) [1]
1.18 – 1.34 m3/t (bulk cargo) [11]
1.34 – 1.50 m3/t (bags) [11]
1.23 – 1.70 m3/t (bulk cargo) [14]
1.42 – 1.53 m3/t (bags) [14]

Angle of repose

Lower limit: 23°
Upper limit: 29°
Average value: 25°

Grain size

Diameter 2 mm, length 5 mm

Stowage space requirements

Cool, dry, good ventilation


Matting, jute coverings. Different types of cereal must be carefully segregated from one another, as mixing gives rise to serious claims.

Cargo securing

In the case of maritime transport, the IMO (International Maritime Organization) „Code for Safe Carriage of Grain in Bulk“ must be complied with.

When loading an ocean-going vessel with several types of cereal, heavy cereals (wheat, rye, barley, corn) must be stowed in the lower part of the hold and lighter cereals (oats, millet) in the upper part of the hold, for reasons of stability.

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Risk factors and loss prevention

RF Temperature

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

Favorable travel temperature range: no lower limit – 20°C

Molds reach optimum activity at temperatures of between 20 and 30°C. In addition, at temperatures > 25°C, metabolic processes increase, leading to increased CO2 production and self-heating of the wheat.

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RF Humidity/Moisture

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

Designation Humidity/water content Source
Relative humidity 70% [1]
Water content 12.8 – 14.0% (Atlantic ports, USA-CAN) [1]
12.6 – 14.0% (Pacific ports, USA-CAN) [1]
Maximum equilibrium moisture content 65% [1]

Classification by water content:

Water content Designation
up to 15% dry
15 – 16% medium dry
16 – 17% moist
17 – 18% wet

Wheat is among those goods which are characterized by their hygroscopicity.

Sorption isotherm, wheat

Figure 5

Moisture, including an excessive water content (> 15%), causes mold, mustiness and fermentation, agglomeration, self-heating and a risk of germination (premature sprouting). The product is then no longer suitable for milling into flour, but instead only for producing spirits.

Problems of moisture may be prevented by suitable pre-drying of the wheat. This is the easiest way of reducing the activity (respiration) of the grain and removing the nutrient medium for mold development and spoilage processes. The necessary level of dryness is approx. 14% water content, which is at equilibrium with relative humidity of 70% at 20°C. The mold growth threshold is reached at a water content of as little as 15% (75% relative humidity).

At 16 – 17% water content, the sorption isotherm climbs sharply, so meaning that equilibrium moisture contents of > 80% very rapidly produce an excessively damp atmosphere.

Individual clusters of damp product may cause considerable damage to the cargo. The wheat in such clusters has a tendency to self-heating. Damp (sweating) wheat then appears in the boundary layers, so allowing the process to develop further. Such clusters may form, for example, in too freshly harvested product (not yet post-ripened) or where damp goods have been loaded.

At water contents of > 17% swelling occurs in addition to fermentation, mold, rot and self-heating. Seawater damage may result in structural damage to the ship due to swelling in the hold. Flour made from seawater-damaged cereal may have a bitter flavor. Where such damage is suspected, a seawater test should be carried out using the silver nitrate method

Odor and flavor changes arising from mustiness due to moisture are not lost in the course of the milling and baking process.

For north Atlantic voyages, a water content of 13% is the optimum value at which the grain is dry for shipment; due to lower temperatures over the winter months, water contents of up to 15% are possible at that time.

At a low water content, the intensity of respiration is low at all temperatures. Even at temperatures of 25°C, respiration intensity is low at a water content of up to 13%. Cereal having a water content of < 13% is thus deemed to be dry for shipment. Harvests from previous years will always be dry for shipment and have a water content of lower than 13%. In this case there need be no reservations about suspending ventilation. When cereal is dry for shipment, the risk of self-heating is slight because the dry grains of cereal absorb the water content from the moister grains.

However, from a water content of 14%, the intensity of respiration begins to rise. Nevertheless, since this intensity still remains low at temperatures of between 0°C and 10°C, the respiration of cereal may largely be inhibited by low transport temperatures. This is also the reason why, in the winter months, a water content of up to 15% is admissible in the north Atlantic region, including the North Sea and the Baltic.

If the water content rises above 15% and elevated temperatures also occur, respiration becomes more intense. This course of events is caused by the enzyme reactions associated with respiration, which are in particular promoted by a relatively high water content and relatively high temperatures, so accelerating respiration.

Water absorption is highly disadvantageous in dry products such as cereals because even small quantities of water may lift the water content of the cereal above the critical point at which a rapid increase in respiration occurs. This also means that, under normal conditions, a reduction in moisture from 16% to 13% has a greater effect than a reduction in temperature from 18°C to 10°C. Compliance with the specified water contents is thus of prime importance if cereal is to be transported without loss.

Prior to loading, the loading moisture content should be checked by an independent inspector and a certificate provided. These certificates should state not only that appropriate measures have been carried out but also how and with what they were carried out and with what level of success.

When cereals are shipped as bulk cargo, lumber used for the grain bulkheads must be air dry, i.e. the water content of the lumber must not be more than 15%. The water vapor released by the lumber may otherwise lead to heating of the cereals and to lump formation along the lumber walls. Spoiled cereals then stay stuck to the bulkheads.

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RF Ventilation

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

Recommended ventilation conditions: surface ventilation.

Ventilation of cereals depends on water content: goods with a water content of < 14% and equilibrium moisture contents of < 70% do not need to be ventilated.

Up to a water content of 15%, surface ventilation is recommended, in order to dissipate CO2, heat and moisture. At the same time, care should be taken to ensure that the surfaces are not cooled too much, to avoid the formation of damp boundary layers beneath the cargo surface.

Wheat releases water vapor constantly, which needs to be dissipated by ventilation. However, caution is advisable on voyages from hot to cold regions (e.g. Argentina to Europe):

Wheat which is not dry for shipment has a particular tendency to self-heating and the flow of heat from the cargo counteracts external cooling, so resulting in the formation of steep temperature gradients in the superficial layers of the cargo. At the same time, water vapor flows from the inside of the cargo to the surface. In the case of simultaneous cooling of the surface by ventilation, the relative humidity increases in the superficial layers of the cargo. If dry fresh air is used for ventilation, a dry surface layer several centimeters thick is obtained, which creates the impression that the cargo is free of all defects. Beneath this is then a damp intermediate layer of lower grade cereal which is starting to decompose, being stuck together and swollen. Such damp intermediate layers are observed relatively frequently.

In order to avoid cargo damage caused by such moist intermediate layers, the fresh air supply must be restricted when there is an excessive temperature differential between the cargo and the external temperature.

Damage to only a proportion of a cargo of wheat is as a rule indicative of the damaged proportion having been stored in a dead air zone, where it was inadequately ventilated.

Damage may also be caused by the ships‘ lying in the roads at the port of destination for an extended period at low external temperatures. The cargo within the stack is, however, still at a higher temperature, resulting in water vapor transport towards the colder parts of the cargo close to the ship’s side, where moisture damage may then occur. Such damage is often associated with the fact that ventilation is stopped when the ship is lying in the roads. Ventilation is, however, essential until the cargo has been unloaded from the ship.

It is essential to be aware of the fact that it is impossible to ensure proper airing throughout a bulk cargo of cereals. Even when ventilation is carried out, the relative humidity of the immobile air between the individual cereal grains is determined by the product’s water content. For this reason, as mentioned above, drying-out caused by ventilation is generally only superficial.

As a result, cereal loaded in an excessively moist state cannot be dried and protected from spoilage by a ship’s ventilation installation.

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RF Biotic activity

Wheat displays 2nd order biotic activity.

It is a living organ in which respiration processes predominate, because its supply of new nutrients has been cut off by separation from the parent plant.

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RF Gases

In wheat, metabolic processes continue even after harvesting. The cereal grains absorb oxygen and excrete carbon dioxide (CO2).

This excretion of carbon dioxide is important from various standpoints:

If relatively large quantities of CO2 accumulate in the hold, the respiratory activity of the cereal will drop. In the case of cereal which is dry for shipment, hold air with an increased CO2 content does not have a negative impact on the quality of the cargo, indeed mold growth is inhibited.

However, if wheat is shipped in closed holds/containers at relatively high water contents, the cereal must be expected to change over from aerobic to anaerobic respiration due to the build-up of CO2, which means, among other things, that lactic acid bacteria, which are able to tolerate an anaerobic environment, can also develop. Due to their toxicity, the resultant fermentation products CO2, lactic acid and alcohol have an impact on the grain germ, especially on seed cereal, which loses its ability to germinate if stored in an oxygen-depleted environment.

Respiration may cause life-threatening CO2 concentrations (TLV: 0.49 vol.%) or O2 shortages in the hold/container. 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

Oil content: 1.9 – 2.0%

Wheat tends towards self-heating due to moisture, inadequate ventilation and elevated stack pressures.

The increase in respiration of the cereal thus results not only in the formation of CO2 and moisture but also in increased evolution of heat. Moisture and heat together in turn promote the activity of the respiratory enzymes, which bring about more rapid respiration, as a result of which this increase in cereal respiration may result in self-heating.

Especially in freshly harvested cereal with average moisture contents of 14%, there is a risk of self-heating because, given the differing stages of ripeness of the individual grains, a proportion of them have higher water contents. Such grains are the starting points for moist spots which expand continuously and finally encompass the entire cargo of cereal with a major rise in temperature.

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RF Odor

Active behavior Wheat has a slight, pleasant odor.
Passive behavior Wheat is highly sensitive to the absorption of foreign odors.

The reason for this is the rough surface and the multilayer husk and seed coat which have cracks and so communicate with the external air. The resultant large overall surface area explains the elevated odor sensitivity of cereal grains.

Gases and aroma substances, such as sulfur dioxide (SO2), phenol and kerosene, are readily absorbed by the cereal. For this reason, holds must be completely odor-free and deodorization must not be carried out only immediately before loading.

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RF Contamination

Active behavior Wheat produces dust during cargo handling and storage.
Passive behavior Especially after the carriage of contaminating (coal, ores, cement), odor-tainting or pest-infested cargoes, fitness for loading must be carefully reestablished by cleaning, disinfection, deodorization and ventilation. An inspection certificate confirming fitness for loading should be provided.

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RF Mechanical influences

Suction and blowing devices may cause damage to the grains during cargo handling.

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RF Toxicity / Hazards to health

Respiration may cause life-threatening CO2 concentrations (TLV: 0.49 vol.%) or O2 shortages in the hold/container. Therefore, before anybody enters the hold, it must be ventilated and a gas measurement carried out.

Contamination of the cereal grains with the ergot fungus (Claviceps purpurea) must not exceed 0.5% of the weight of all admissible contaminants.

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RF Shrinkage/Shortage

Evaporation of the intrinsic moisture content may result in a weight loss of up to 1% (US Gulf approx. 0.5 – 0.7%, North America and east coast approx. 0.3%).

Further losses may arise due to adhesion to the hold walls and dust formation during cargo handling.

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RF Insect infestation / Diseases

Wheat may be infested by the following cereal pests during storage and transport:

by the granary weevil (Sitophilus granarius)
by the cadelle beetle (Tenebroides mauretanicus)
by the rust-red grain beetle (Cryptolestes ferrugineus)
by the sawtoothed grain beetle (Oryzaephilus surinamensis)
by the European grain moth (Nemapogon granellus)
by the Angoumois cereal moth (Sitotroga cerealella)

The chewing damage caused by the cereal pests brings about increased respiration in the cereal (hot spots) and this, associated with the metabolic activity of the pests themselves, promotes evolution of heat and moisture, which in turn provide favorable living conditions for molds and subsequently, at very high moisture levels, for bacterial growth.

Insect infestation (granary weevil, weevils etc.) may result in self-heating which ultimately gives rise to depreciation and finally total loss.

Inadequately cleaned warehouses and holds/containers are generally the root cause of insect infestation.

Cereal is also at risk from rats and mice, which can act as disease vectors and contaminate the cereal.

Before loading, holds/containers should be examined by an independent inspector for infestation by pests of any kind and an appropriate certificate obtained.

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