Transporting freshly cut flowers can be a real challenge and managing the cool chain well should bring large commercial benefits. The following article looks at some of the issues involved.

We are going to talk about the global export market for cut flowersand in particular roses from the second largest exporting country of Columbia.

Columbia satisfies many requirements from producers:

1. Good climate
2. Closeness to market, in this case Miami, Florida
3.Cheap labour.

The two key indicators for quality exporting are
2.Vase life.

These terms are used by the industry to discuss the main ways quality can be lost

1. Flower senescence. Basically ageing. Some flowers such as daisies or orchids have
a long life. Others like tulips are very short lived.

2.Wilting.Lack of water.

3.Leaf yellowing and senescene.

4.Shattering, loss of leaves, buds or petals.Often caused by the presence of ethylene in the air.

Factors which impact post harvest maturity include

1. Flower maturity.Is the harvesting before or after the buds have opened.

2. Respiration. Flowers grow and age and a key element of this process is respiration. The faster the respiration the faster a plant will age. For instance at 30 degrees C it will respire up to 45 timesquicker than at a room temperature of 2 degrees C. The impact of temperature is so strong thatground transport in a continuously cold temperature can be better for the flowers than air transport in non cooled environment.You can slow the rate of ageing by storing the flowers with water provided for the stems , as opposed todry storage, but even this won’t completely eliminate the faster ageing in a non temperature controlled room.

The optimum storage temperature is usually around 0 degrees C but some more exotic plants shouldn’t be cooled below 10 degrees C otherwise more damage can occur.

Sugar pulsing. Basically the stems are given a sugar boost by standing in a solution for up to 24 hours.

Light. Light or darkness is not usually a problem but there are a few cases where darkness can harm the flowers.However some flowers, such as a chrysanthenum, could yellow if stored in a warm temperature in the dark.

Humidity and water supply. Cut flowers have a large surface area and to avoid excess water loss the humidityshould be above 95%.You can rehydrate flowers but it is usually better to maintain their water content
as much as possible.

Air embolism. Basically air bubbles in the lower part of the stem and these bubbles will slow or preventwater being drawn up the stem. There are quite a few ways to remove them.

Bacterial plugging. The cut stems release cells, proteins and so on into the vase where basteria can breed on them.The slime can then hinder the uptake of water into the stems.

Hard water. Hard water contains minerals and this can produce an alkaline solution. A high PH can really reduce the uptake of weater.

Water quality. Chemicals such as sodium and fluoride commonly found in tap water can be harmful to many plants.

Ethylene.When present this gas can be really dangerous for many cut flowers. Ethylene can come from the natural ageing process but also from the combustion of organic materials such as wood, gasoline and so on.A low temperature can dramatically reduce teh natural production and uptake.

Growth tropisms or movement in response to environmental stimuli. Typically geotropism where the stems bend away from gravity or phototropism where the stems bend towards light. A low temperature greatly reduces geotropism.

Mechanical damage. Damaged plants produce more ethylene and have a higher espiration rate.

Disease.Transfer from cold storage to warmer handling areas can cause water to condenseon the leaves.Grey mold growth is then encouraged by the moisture.

Let us now look at the role of cooling within the process.

We have already seen how the cut flowers are largely best suited to a 0 degrees C temperature.Ideally they would be packed in the cold room to avoid temperature gradients and the formation of moisture.
However this isn’t always popular with packers and can be more expensive.

Packed flowers are difficult to cool. Forced air cooling pushes cold airthrough the packaging.Fans play a large role in this process and most flowers can be force cooled in under 45 minutes.

The time required to reach the optimum temperature is usually represented by a cooling curve.In the flower industry they talk of a 7/8ths cooling time which is, not unexpectedly, the time needed to to 7/8ths of the way to the ideal cool temperature.Typically this might be just half an hour, but to get all the way to zero degrees C that might require 2 hours.

Care must be taken to ensure the cooled air can flow through the packed boxes.
Fans. Forced air coolers use either centrifugal or squirrel cage or alternatively propeller or axial flow fans. Fans are selected on two criteria, the airflow and the air pressure generated.

Tropical flowers have their own challenges.Typically they are stored in the centre of a load
and away from direct cooling fans. They are better suited for fast air transport as well.

Cooling for aquapacks. Modern trends often favour shipment with water. Pre cooling of these boxes can be a real challenge.

Vacuum cooling. Lower air pressure means a lower boiling point and so on down the temperature ladder. Basically it is quicker and easier to cool the boxes. However capital costs are very high.

Irradiation. Often used to ensure sterility before border crossings. Impact on cooling and vase life is unpredictable.

Looking at the supply chain as a whole.

Probably the weakest point in the supply chain is the loading of the flowers at the airport. The ideal time slot for flower shipmentsis during the cool of the night and this also ties in with economic savings for the airlines with the planes needing less fuel for night time take offs in the cooler air.

However the flowers might well arrived stressed, the pallet handling might not be ideal and they can often wait in uncooled bays for up to 4 hours. The planes themselves are rarely refrigerated and overall these issues will significantly reduce the vase lifeof the flowers.

Temperature management before loading onto the plane.
Some suggestions include
1. Consolidation onto pallets to reduce surface area exposed.
2.Keep in a shaded location.
3.Close pre cooling vents and keep the pallets covered with light white sheets.As an indication of the temperature dangers :

“Flowers cooled to 0°C and packed in a large pallet will gain about 1°C per hour due to the heat generated by the process of respiration. As the temperature rises, respiration rises, and the heat gain increases too, so that by the time the flowers are at 10°C they may gain 3°C per hour, and once they are at 20°C, the heat gain can be as much as 10°C per hour. Flower boxes unloaded from aircraft pallets have been probed at temperatures as high as 55°C, indicating the runaway danger of inadequate temperature management and delays in transport. ”

One final problem is that flower boxes come in many different sizes. This makes it really important to try and square off the pallets. Ensure that they have square corners and will fit together well.


PDF report on the cool supply chain issues

And of course the blog which inspired this post