| dc.description.abstract | This research was conducted at the University of Nairobi with the broad
objective being to determine the influence of the parchment hull on the thinlayer
drying of parchment coffee.
Parchment coffee consists of a soft tissue bean enclosed in a woody husk
(the parchment hull). Drying of parchment coffee is very important in
maintaining the intrinsic high cup quality. The convectional drying process is
sun drying, a process that consumes large ground space, is labour intensive,
takes long and is vulnerable to bad weather. However, research has shown
that the parchment coffee can be partly dried using mechanical dryers without
significant loss of quality. In the development of mechanical dryers, the role
of the thin-layer equation for accurate prediction of the drying process is
pivotal, yet none existed for parchment coffee.
A laboratory dryer with air conditioning system was designed and fabricated
for thin-layer drying studies. The dryer was tested and found to provide
constant drying air conditions for temperature ranges between 31 and 66°C
Data were collected for five thin-layer drying conditions for the parchment and
the green coffee beans respectively. The drying conditions were composed of
five dry bulb temperatures viz. 31°C, 38°C, 46°C, 50°C and 66°C and one dew
point temperature viz. 14°C.
A mathematical model based on the Fick's second law of diffusion was
developed to describe thin-layer drying of parchment coffee. Further two
mathematical models were selected from literature. The models selected were
the diffusion model and the Page equation. The proposed model and those
selected from literature were evaluated to fit the data.
The results of the drying experiments indicated that the time taken to achieve
any given moisture ratio was shorter for the green coffee beans than for the
parchment coffee beans, hence the parchment hull retards the drying rate of
parchment coffee beans.
The Page equation was found most suitable for describing thin-layer drying of
parchment coffee beans for the drying air temperature range of 31 to 66°C,
relative humidity of 3 to 31% and air velocity of 0.6 m/s.
UoN· | en |
