Measurement of Electric Impedance of Cream during Whipping

Abstract

Electric impedance of cream was measured during whipping in order to clarify the optimum end point of the process. A small electric mixer (Kenwood Mfg. Ltd) which has the mechanism simllar with industrial scale machine was used for whipping, and parallel copper electrodes were fixed to the bottom of the bowl. The electrodes have 40mm length and 0.7mm diameter and are set 2.3mm apart from each other. The impedance was determined at 100kHz with a Vector Impedance Meter 4800A (Hewlett Packard Ltd.) connected to the electrodes. Impedance curve showed a slow increase at the initial stage, followed a remarkable increase and reached a peak, then decreased rapidly. The optimum end point of whipping could be determined on a final region at gradually increased curve comparing other various physical properties, i.e. overrun, visco-elasticity, separation to layers by centrifugal force, spreadability, smoothness and syneresis of whipped cream. Sucrose inceased the slope of impedance curve and delayed the optimum end point of whipping. At the initial part of the impedance curve, the curve of milk fat cream showed a gradual increase, but that of vegetable fat cream continued with a long plateau region to the end point of whipping. Increase of impedance of cream during whipping was regarded to be due to the increase of foam content.