3. Results and discussion
3.1. Drying kinetics and modeling
The drying kinetics of the cocoa beans dried artificially inside
the oven are as shown inFigs. 2 and 3. The initial moisture content
before drying was about 52% ± 0.928 w.b. (mean ± std. deviation).
As expected, the drying temperature had a significant effect on
the drying kinetics of the samples. The moisture content decreased
continuously with time and an increase in temperature resulted in
reduced drying time. The longest and shortest drying time were recorded at 52 h (60C) and 30 h (80C), respectively. Two separate
tempering periods (TP1 and TP2) were present in the 60C treatment while only one was present (TP1) in the 70 and 80C treatments. The drying rate curves showed falling trend beyond
moisture content of 45%, 42% and 52.7% at drying temperatures
of 60, 70 and 80C, respectively. A short initial warming up period
was observed in the early stage of the 60 and 70C treatments but
the length of this period was unable to be determined due to the
short time interval used (2 h).Bravo and Mc Gaw (1974)have reported occurrence of this period in cocoa drying at the initial
0.3 h of the drying process and followed by a constant rate period
thereafter that last for not more than 2 h (drying temperatures
range 55–86C). This is quite similar to those observed in the 60
and 70C treatments.
The 80C treatment showed the highest drying rates curve as
compared to the other two treatments (Fig. 3). The highest drying
rate achieved in 80C was 0.0797 (g water/g wet solid h) while at
70C and 60C were 0.047 (g water/g wet solid h) and 0.0389 (g
water/g wet solid h), respectively. It can be seen that at higher
moisture content the increase in temperature has more considerable effect on the drying rates as compared to lower temperature