Effect of spray-drying conditions on moisture content and particle size of coffee extract in a prototype dryer

In this study the effect of spray drying conditions on moisture content and particle size of coffee extract was researched. The factors investigated were the inlet temperature (150 to 220 °C), air flow (537 to 691 kg·h), and the frequency of the rotary atomizer (60 to 90 Hz). Analysis of variance revealed that the independent variables had significant effects (p < 0.10) on the response variables. An increase in frequency of the rotary atomizer from 60 Hz to 90 Hz produced an increase in outlet temperature; and therefore, a decrease in product moisture content. The luminosity of the powders increased as the inlet temperature and air flow increase from 145 °C to 220 °C and from 537 kg·h-1 to 691 kg·h-1, respectively; therefore, the powder coffee turned brighter. A decrease in hysteresis was observed with an increase in the air flow rate from 537 to 691 kg·h.

Keywords: spray drying, coffee, particle size, sorption isotherms, GAB and BET model.