The effect of ultrafiltration on the subsequent concentration of grape juice by osmotic distillation

The potential for osmotic distillation flux enhancement in grape juice conc entration by ultrafiltration pretreatment has been investigated using ultra filtration membranes with a range of pore diameter/MWCO values. Juice visco sities were determined over the concentration range to assist with interpre tation of the flux data. Ultrafiltration using membranes with pore diameter s of 0.1 mu m or less resulted in appreciable osmotic distillation flux inc reases over that observed for juice not subjected to ultrafiltration. These flux increases have been attributed to a reduction in the viscosity of the concentrated juice-membrane boundary layer as the result of protein remova l. HPLC measurements showed that the normal concentration of fermentable su gars in standard 68 degrees Brix concentrate can be achieved at a lower Bri x value with UF permeate, thereby providing a possible means of reducing th e handling of highly viscous streams. Ultrafiltration also resulted in an i ncrease in juice surface tension with a consequent reduction in the tendenc y for membrane wet-out to occur. (C) 2000 Elsevier Science B.V. All rights reserved.