Lemons [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 Zitronen
English Lemons
French Citrons
Spanish Limónes
Scientific Citrus limon, Citrus medica
CN/HS number * 0805 30 ff.

(* EU Combined Nomenclature/Harmonized System)

Product description

Lemons belong to the rue family (Rutaceae) and come originally from Asia.

In addition to lemons, the group of citrus fruits, which are mainly cultivated in subtropical regions, also includes oranges, grapefruits, mandarins, limes and easypeelers.

Lemons are berry fruit consisting of three layers:

the outer yellow peel (exocarp, flavedo), the glands of which exude the essential oil of lemon, which produces the typical citrus odor
the whitish mesocarp (albedo)
the endocarp consisting of 8 - 10 segments filled with juice sacs (vesicles)

Lemons are usually of an elongated shape with a peel of variable thickness and pointed tip. The juicy pulp of a medium-sized lemon contains 30 - 35 g of lemon juice, which has a high vitamin C content (60 - 100 mg per 100 g of fruit). Lemons are divided into winter and summer fruits.

The degree of ripeness of citrus fruit is determined on the basis of three criteria:

by the ripeness index: this is determined by the Brix value, which is a measure of the sugar/acid ratio of the fruit. According to [7], citrus fruit with a Brix value of between 10 and 16 have good flavor.
by cutting at purchase: freshness is determined by cutting the fruit in half from the stem-end to the opposite end. If the fruit is withered at the stem-end, it must not be shipped.
by peel color: the color of the peel is not necessarily a reliable indicator of ripeness, but its surface gloss is. Glossy lemons are ripe, even if they are still green or have green spots.

Fungicides are diphenyl, orthophenylphenol (OPP) and thiabendazole (TBZ). Diphenyl can be recognized from its naphthalene-like odor. The fungicides primarily prevent blue and green molds, but they do impair flavor and indication of their use is mandatory.

Quality / Duration of storage

The fruits should have thin peel, be nearly seedless and very juicy, i.e. have a minimum juice content of 20 - 25%, be undamaged and unmarked (dry and hard peel and spots indicate over-aging and off-flavors) and have a firm, glossy peel.

Experience has shown that it is the care taken with preparation of the fruit for shipping which very largely determines whether individual batches withstand the rigors of transport. Such preparation for shipping is carried out in packing houses. These include:

Post-ripening of green or unsatisfactorily colored fruit to achieve a salable peel color in ripening rooms.
Removal of dirt, sooty mold, spraying residues and scale insects in washers.
Coating with a layer of wax and treatment with preservatives and marking accordingly.
Grading of the fruits by size (gaging), color and other external features.
Counting, weighing and packing. Marking each package with details of number of fruit, quality class, variety and origin.
Storage until shipment in cold stores.

Waxing to prevent loss of aroma and weight is required because the washing process removes the natural wax layer. The film of wax sprayed onto the peel only partially seals the pores so that the fruits are still able to respire.

Maximum duration of storage and transport is as follows:

Designation Temperature Rel. humidity Max. duration of storage Source
  10 - 11°C 80 - 90% 12 weeks [1]
  12 - 14°C 85 - 90% 16 - 24 weeks [5]
Green lemons 12 - 14°C 85 - 90% 4 - 20 weeks [39]
Yellow lemons 10 - 11°C 85 - 90% 4 - 6 weeks [39]

Where controlled atmosphere transport is used, transport and storage duration may be extended. The following parameters apply in such a case [16]:

Temperature Rel. humidity O2 CO2 Suitability for controlled atmosphere
10.0 - 12.8°C 85 - 90% 5% 5 - 10% good

Intended use

Since lemons are citrus fruit having a juicy/aromatic flesh with a high acid content, they are primarily used for their juice and for seasoning. The flesh and juice are used to make lemonade, soft drinks, jams and the like, while the highly fragrant lemon oil is extracted from the peel in the countries of cultivation.


(Click on the Figure to enlarge it.)

Photo, lemons

Figure 1

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 Spain, Italy, Turkey, Cyprus
Africa South Africa, North Africa, Egypt
Asia Israel, India
America Chile, Uruguay, Argentina, USA, Brazil, Mexico

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Lemons are transported in boxes and cartons.

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Symbol, general cargo

General cargo


Means of transport

Ship, aircraft, truck, railroad

Container transport

Refrigerated container with fresh air supply or controlled atmosphere.

Cargo handling

Because of its impact- and pressure-sensitivity, the fruit has to be handled with appropriate care.

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

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

Stowage factor

1.71 m3/t (cartons on disposable pallet) [1]
2.55 - 2.80 m3/t (boxes and cartons) [14]

Stowage space requirements

Cool, dry, good ventilation


Fiber rope, thin fiber nets, wooden dunnage

Cargo securing

Because of its considerable impact- and pressure-sensitivity, packages of this cargo must be secured in such a way that they are prevented from damaging each other. Spaces between packages or pallets must be 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

Lemons 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 Tables merely constitute an estimate of appropriate temperature ranges. Temperatures may deviate from these values, depending on the particular transport conditions.

Designation Temperature range Source
Travel temperature 10 - 11°C [1]
10 - 13°C [2]
12 - 14°C [5]
10 - 12°C [6]

The cargo and holds/containers should be precooled prior to loading.

Depending upon the species and variety, all citrus fruits are highly cold-sensitive. Grapefruit, lemons and limes are more susceptible to chilling damage than are oranges and mandarins, and late-ripening varieties are more temperature-sensitive than early varieties. While oranges can withstand temperatures of 5°C, more temperature-sensitive types should never be shipped below 10°C. Green citrus fruits require higher transport temperatures than do yellow; the higher is the acid content of the fruit, the greater is its cold-sensitivity.

Chilling damage is manifested in citrus fruits in particular by spots on the peel (brown dots on the peel), accompanied by a bitter taste and unpleasant odor, rot and cell wall collapse. The glossiness of the peel is lost and the albedo layer (inner layer of the peel), which is normally white, turns a dark color. When the fruit is divided up, the segments, which have a low juice content, break up and the whole fruit is glassy and soft. The severity of the chilling damage is determined not only by the extent to which the temperature has fallen beneath the limit, but also by the length of exposure to this temperature. Chilling damage does not generally occur in cold stores, but instead prior to cooling or after leaving the cold stores.

Excessively rapid warming of refrigerated fruit results in condensation and spoilage.

During loading, pulp temperature measurements must be performed continually. The pulp temperature must never be < 4°C or > 25 - 30°C as storage life and appearance are impaired outside this range. Fruits punctured for pulp temperature measurement must be discarded as they would rapidly spoil and infect the other fruit. The measurements must be recorded.

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RF Humidity/Moisture

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

Designation Humidity/water content Source
Relative humidity 80 - 90% [1]
85 - 90% [2]
85 - 90% [5]
85 - 90% [39]
Water content approx. 90% [1]
Maximum equilibrium moisture content 85% [1]

It is essential to protect lemons from moisture (seawater, rain, condensation, snow) as moisture in particular promotes green and blue mold and black rot.

In general, due to the high water content of lemons of approx. 90%, a relative humidity of 85 - 90% is required. Only lemons, oranges and mandarins with a dark green peel color are able to withstand a relative humidity of 82 - 85%.

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RF Ventilation

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

Recommended ventilation conditions: circulating air, 40 - 60 circulations/hour with continuous supply of fresh air

The addition of fresh air is extremely important as citrus fruit can start to ferment within a few hours due to anaerobic respiration (resulting in total loss of the fruit). If ventilation is inadequate, storage damage may occur, taking the form of a bitter flavor and peel scab.

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RF Biotic activity

Lemons 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).

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RF Gases

CO2 evolution at 10°C: 12.5 mg/kg*h [1]
Upper limit of permissible CO2 content 0.1 vol.% [1]

< 0.5 vol.% [39]
Ethylene evolution  
Active behavior The rate of ethylene production is very low, being below 0.1 µl/kg*h [16].
Passive behavior Lemons are moderately sensitive to ethylene [16] and should thus not be stored with goods having an elevated ethylene production rate (allelopathy).

In fresh fruit, metabolic processes continue even after harvesting. The fruit absorbs oxygen (O2) and excretes varying amounts of carbon dioxide (CO2) and ethylene (C2H4) as well as aromatic compounds during the conversion of starch into sugar (ripening process).

Levels of respiratory gases which promote ripening, such as ethylene as well as carbon dioxide, should be kept as low as possible. If ventilation is inadequate, storage damage, such as a bitter flavor and peel scab, may occur. The supply of fresh air must thus be constant in order to dissipate these gases.

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RF Self-heating / Spontaneous combustion

No risk.

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RF Odor

Active behavior Lemons have a strong, pleasant odor. Due to their high content of highly volatile essential oils (formic acid, acetic acid, ethanal, ethylene and the odor substance limonene), citrus fruits are in general a highly odor-contaminating cargo and must thus not be stowed or stored together with fruit, vegetables and other odor-sensitive foodstuffs.
Passive behavior Lemons are highly odor-sensitive.

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RF Contamination

Active behavior Lemons do not cause contamination
Passive behavior Lemons are sensitive to contamination by dust, dirt, fats and oils. The holds or containers must accordingly be clean and in a thoroughly hygienic condition before loading.

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RF Mechanical influences

Lemons are highly impact- and pressure-sensitive. Spoilage due to mold and rot occurs in particular when the peel of the fruit is injured. Injury to peel occurs in the event of careless harvesting and due to incorrect handling of packages. Such injury may also be a sign of excessively low temperatures or incorrect use of postharvest phytosanitary agents.

Attention must be paid to the level of filling of cartons in order to avoid damage: they should be filled no higher than the top as overfilling will inevitably result in pressure damage, and thus premature spoilage, when the cartons are stacked. Bruises become soft and the squashed peel looks like "goose-pimples". The aroma of the fruit is also lost and the flavor becomes bitter and unpleasant.

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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.%.

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RF Shrinkage/Shortage

The normal weight loss due to a reduction in the moisture content of the product is approx. 1 - 2% [1].

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RF Insect infestation / Diseases

Blue mold rot or storage rot is the most feared storage disease of citrus fruits and is caused by two species of mold: green mold (Penicillium digitatum), which is of an olive-green color, and blue mold (Penicillium italicum), which is of a blue-green color. Lemons are primarily attacked by green mold. The fungal spores mainly penetrate through small injuries and initially form white, circular spots of fungal growth, which are subsequently covered from the center outwards with a green or blue-green sporulating layer. The peel becomes spongy, the pulp soft - a typical instance of wet rot. Development is optimal at 20 - 27°C; growth still flourishes at 10°C and comes to a standstill only at 4°C. Blue mold is transferred from fruit to fruit by contact.

Seawater, rain and condensation water promote green and blue mold growth.

Photo, green mold

Figure 2
Photo, green mold

Figure 3
Photo, green mold

Figure 4

Black rot (beginning at flower end) and stem-end rot (beginning at stem-end) are forms of dry rot which may occur as early as during harvest. Moisture promotes blue mold rot and black rot.

The Mediterranean fruit fly (Ceratitis capitata), a quarantine pest, in particular attacks thin-peeled citrus varieties, especially oranges and mandarins. The 8 mm long maggots of this boring fly in particular attack ripening and ripe fruit, causing rotting. Complete destruction of affected fruit and the use of contact insecticides during the flight time are the most effective methods of control. Countries apply strict quarantine measures to prevent introduction of this pest. Import of affected fruit is prohibited. Since these pests have many different food sources, they can find food throughout the year in the Mediterranean region; in January mandarins are attacked, from February to May early to late oranges, in the summer peaches, apricots and pomaceous fruit and, at the beginning of winter, back to mandarins. Externally visible signs of attack are sunken, soft, black puncture marks and, subsequently, brownish discoloration of the peel.

The quarantine regulations of the country of destination must be complied with and a phytosanitary 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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