Abstract
Changes in the projected area (PA) of particles of an instant coffee powder were followed in real time by videomicroscopy and image analysis. Particles were placed inside a transparent acrylic chamber (7 × 7 × 3 cm) where the relative humidity RH (43%, 52%, 67% and 74%) and temperature T (20, 25 and 30 °C) were controlled and measured in the head space. A “caking index”, ϕ, was defined as the change in PA at any time t with respect to the initial PA. At any temperature, there was an increasing effect in ϕ as RH increased and the shape of ϕ versus time curves closely followed that of caking, measured by sieving techniques. The exponential kinetic model adequately fitted the data. The PA method could be used as a first approximation to predict the tendency to caking of amorphous particles.
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