Dielectric spectroscopy (DS) is routinely used in yeast and mammalian fermentations to quantitatively monitor viable biomass through the inherent capacitance of live cells: however, the use of DS to monitor the enzymatic break down of lignocellulosic biomass has not been reported. The aim of the current study was to examine the application of DS in monitoring the enzymatic saccharification of high sugar perennial ryegrass (HS-PRG) fibre and to relate the data to changes in chemical composition. DS was capable of both monitoring the on-line decrease in PRG fibre capacitance (C = 580 kHz) during enzymatic hydrolysis, together with the subsequent increase in conductivity (G = 580 kHz) resulting from the production of organic acids during microbial growth. Analysis of the fibre fractions revealed >50% of HS-PRG lignocellulose had undergone enzymatic hydrolysis. These data demonstrated the utility of DS biomass probes for on-line monitoring of simultaneous saccharification and fermentation (SSF). (C) 2011 Elsevier Ltd. All rights reserved.