Pulsed electric field enhanced expression and juice quality of white grapes

This work discusses effects of PEF application on mechanical expression and characteristics of juice (absorbance A, and turbidity T) from different white grapes (Muscadelle, Sauvignon and Semillon), purchased from an experimental vineyard of Bordeaux region. The experiments were carried out using a laboratory filter-press cell, equipped with PEF treatment system, operated at moderate electric field strength (E = 250-1000 V/cm) and at constant pressure (P = 5 bar). The PEF treatment results in increase of the juice yield from 49-54% to 76-78% at 45 min of pressing. The data obtained on A, and T evidence the noticeable improvement of juice quality for studied varieties of grapes and juice yield enhancement after the PEF application. The PEF pre-treatment before pressing was found to be more efficient than intermediate PEF treatment during the pressing. The influence of electrical energy input W on extraction kinetics and qualitative characteristics of juices are discussed. The energy input of order W approximate to 20 kJ/kg at electric field strength E = 750 V/cm was shown to be sufficient for optimum PEF-assisted expression. The results evidence that PEF enhanced expression is promising for production of higher quality juices in wine industry. (c) 2006 Elsevier B.V. All rights reserved.