Western and Central Africa
Eastern and Southern Africa
Eastern Europe and Central Asia
Condensation occurs because moisture is always present in the
air and hygroscopic (water-attracting) materials such as coffee
normally contain a certain amount of moisture as well. Coffee with
a moisture content in excess of 12.5% (ISO 6673) should never be
shipped, whether in containers or bagged, as beyond this point the
risk of condensation and therefore fungi growth occurring becomes
unacceptably high. The only exceptions could be specialty coffees
that traditionally have a high moisture content, such as Indian
This is not to suggest that a moisture content of 12.5% is
commercially acceptable for all coffee - for certain coffees,
certain origins and certain buyers it is definitely not *. The
figure of 12.5% simply represents a known technical point at which
the risk of damage from condensation and growth of mould during
storage and transport becomes unacceptably high. Shippers who
normally ship their coffee at moisture percentages below 12.5%
should definitely continue to do so.
An increasing number of buyers now include a maximum permissible
arrival moisture content in purchasing contracts. Increasing
preoccupations with food health and hygiene in consuming countries
suggest strongly that exporters will be well advised therefore to
acquaint themselves with their buyers' requirements in this
Coffee is often loaded in tropical or otherwise warm areas for
discharge at places where the temperatures are very much lower.
Warm air holds more water vapour than cold air; when warm, moist
air cools down to dew point, then condensation occurs. Dew point is
the temperature at which a sample of saturated air will
Put differently: coffee travelling from producing countries during
the Northern Hemisphere summer experiences much less temperature
change than when travelling during the Northern Hemisphere winter.
Vessels may then arrive when snow and ice conditions are prevalent,
particularly in Northern Europe and Scandinavia.** Of course such
conditions are entirely beyond anyone's control, including the
shipping company. On other routes cargo may experience multiple
climate zones during transit. For example from the Pacific Ocean
ports of Guayaquil (Ecuador) and Buenaventura (on Colombia's
West Coast) to the US East Coast (Atlantic Ocean). When passing
Cape Hatteras in the State of North Carolina on the US East Coast
vessels may in winter sometimes experience a drop in outside
temperature of up to 20 degrees Celsius, in just four
The only answer to all such weather-related events is to
exercise the utmost care when lining and stuffing containers, and
to ensure correct stowage on board ship.
For more on this and containerization generally go to www.tis-gdv.de = Transport
Information Service of the German Insurance Association.
Alternatively, contact your local shipping company representative
for information on container stuffing and related issues.
However, to explain briefly...
During transit the temperature outside the container gradually
cools down and the steel container allows the chill to conduct from
the outside of the panels through to the inside. On arrival the
container has cool roof and side panels, and moist warm air in the
space above the cargo and within the stow. Most of the moisture
will have been given up by the coffee beans themselves.
When the temperature of the panels falls below the dew point of
the air inside the container, condensation starts and will continue
until the dew point of the interior air falls to that of the air
Apart from making sure that the coffee has an acceptable
moisture content, condensation cannot really be avoided and all one
can do is try to prevent the condensation falling onto the coffee
as droplets. If temperature changes are gradual and enough time
passes then the coffee beans will absorb the excess moisture from
the air within the container and the container will again be 'dry'.
But temperature differences of 8 to 10 or more degrees over short
periods of time almost inevitably will result in condensation
taking place. In severe cases water droplets, mostly consisting of
dislocated moisture from the coffee itself, form on the interior
roof and side panels, and then drip on to the cargo causing water
damage and mould.
In summary, differences in temperature plus the time factor and
the speed of events combine to release moisture from the coffee.
Given enough time the coffee surface will reabsorb the moisture. If
events unfold too fast or there is too much moisture, then the
coffee cannot reabsorb what it gave up and condensation will
continue as long as the temperature difference between the steel of
the container and the air inside it is greater than 8 degrees. A
simple demonstration: a glass of cold beer 'sweats' because its
temperature is below the dew point of the surrounding air. The
moisture on the outside of the glass comes from the surrounding
air, not from the beer or the glass itself. When the glass warms
up, its temperature eventually reaches that dew point, which causes
the moisture on the outside to dry again: it evaporates back into
the surrounding air.
In producing countries condensation occurs when containers are
stuffed at high altitude locations with high temperatures during
the day that fall rapidly at night, leading to the same scenario.
The risk is increased if full containers are left outside in the
radiant heat of the sun, so containers should not be stuffed too
far ahead of the actual time of shipment.* In certain areas there are shippers who habitually ship at
higher moisture contents but the Coffee Guide is not in
a position to express an opinion on this.
** Container vessel in Finland during winter, covered in
Photograph courtesy Maersk Line Cargo