Rokia Delmas: Experimentation on cocoa beans
Experiment 1: Buoyancy
tests and observation of the behaviour of cocoa beans
Three hundred containers of coca beans measuring 20 feet and filled
80% full (CMA-CGM information) were onboard the vessel. Upon request
from the Préfecture Maritime, Cedre set up an experiment
which aimed at finding out about the behaviour of cocoa beans in
case the containers fell into the water in the weeks following the
incident. A sample of cocoa beans was sent to Cedre in order to
study their behaviour in seawater and to be able to answer questions
on their floating capacity and the potential risks for the environment.
On
31 October, a sample of beans was placed in a crystallising dish
filled with seawater. Nearly all the beans in the sample floated.
Only a few beans immediately sank. After soaking in seawater for
40 hours, nearly all the beans were still floating, but were slightly
immersed.
By
the third day of immersion of the beans, a great abundance of matter
in suspension in the water was observed, and the water had become
very turbid. The cocoa beans were sticky to touch, but remained
firm. This behaviour could be explained by their high fat content
(cocoa butter). On the fourth day, a deposit of matter on the bottom
of the beaker was observed. Over time, an increasing proportion
of beans sank and a white oily film on the surface indicated the
release of lipids. At this stage, there was still no noticeable
release of gas, nor any odour of rotting.
Experiment 1: Appearance of the cocoa bean after rinsing,
after 14 days of immersion in seawater (Source: Cedre)
After 14 days, some beans were removed and rinsed. Observation showed that only the protective cuticle around the bean had started to disintegrate; the bean itself still appeared intact.
Experiment 2: Monitoring of gaseous release in an anaerobic
environment
In a second experiment, a sample of beans was placed in seawater
in anaerobic conditions. A system was set up to recover any gas
released.
At the beginning of the experiment, the cocoa beans were all at the surface. As the days went by, the beans began to sink to the bottom of the flask. By the seventh day, many cocoa beans had settled to the bottom, but they could not however be quantified due to the cloudiness of the water, which inhibited visibility.
A release of gas was observed soon after the
experiment began. Four days later, the gas was measured using a
Draeger tube and the presence of hydrogen sulphide was not detected.
The quantity of water in the flask gradually
decreased and the volume of gas released increased. After 14 days,
a foul odour of decay could be detected. From this date the volume
of gas released began to decrease.
After the experiment had run for two and a half
months, the presence of hydrogen sulphide was measured again, this
time giving a positive indication for the presence of hydrogen sulphide,
this gas being generated by the fermentation of the cocoa beans, which
had been left in seawater in an anaerobic environment.
Experiment 1: Dry cocoa beans immersed in seawater (Source: Cedre)
Experiment 1: Beans immersed in seawater after 40 hours (Source: Cedre)
Experiment 1: Third day of immersion in seawater (Source: Cedre)
Experiment 2 set up to recover the gas released by the beans (Source: Cedre)
Last update: 15/01/08