Behaviour of falling-film freeze concentration of coffee extract

Abstract

The behaviour of falling-film freeze concentration of coffee extract was studied through determining the solute inclusion in the ice produced in a single-plate freeze concentrator. The effect of the initial coffee mass fraction of the extract, the average ice growth rate and the film velocity were studied. The coffee extract at four coffee mass fractions (0.05, 0.15, 0.25 and 0.35 w/w) was freeze concentrated at three different cooling temperatures (-10, 15 and 20 degrees C) and three flow rates (5 x 10(-5), 7.5 x 10(-5) and 10 x 10(-5) m(3) s(-1)). The solute inclusion in the ice and the effect of each parameter were determined. The coffee mass fraction, ice growth rate and film velocity affected the average distribution coefficient. The coffee mass fraction had the greatest effect on average distribution coefficient. The Chen model parameters to predict the average distribution coefficient and the concentration index were found. A logistical model was proposed to predict the concentration reached in successive stages, which tended to 35% at the studied intervals. The model showed an adjusted regression coefficient of 0.98 and the experimental values were within the 95% confidence intervals. The model can be used to predict the behaviour of falling film freeze concentration of coffee extract; this technique is an economic and simple alternative to conventional freeze concentration. (C) 2014 Elsevier Ltd. All rights reserved.