Rheological behavior of mucilage obtained from two varieties of coffee
grown in Colombia (Caturra and Colombia) was studied as a function of
ripe cherry content (RCC) and postharvest time (PHT). A Brookfield HB
DV-III viscometer was used in concentric cylinder geometry over a she
ar rate range of 4.8 to 120 s(-1). The power-law model was used to des
cribe the shear stress versus shear rate data, and the consistency ind
ex (K) and flow behavior index (n) were determined. The mucilage is a
highly viscous and pseudoplastic (n < 0.3) fluid. The K increased and
n decreased as the RCC and PHT increased. The mucilage of the Caturra
variety was more viscous and shear thinning than that of the Colombia
variety. Microstructural examination of the mucilage revealed that cer
tain weak structures as phloem vessels found in the mucilage may be de
stroyed upon application of shear stress and may contribute to the pse
udoplastic nature of the mucilage. Diffusion of tannin from the pulp t
o mucilage with delay in postharvest processing may be responsible for
increased apparent viscosity with increased PHT.