Pretreatment of wood chips with lignin-degrading fungi can save substa
ntial amounts of electrical energy during a mechanical pulping process
. In order to optimize this process, a rapid and reliable method was n
eeded to predict energy savings. In this paper, we examine a fiber sta
ining method that involves the use of Simons stain. This stain for mic
roscopic examination of pulp fibers has been used previously to evalua
te the degree of fibrillation in beaten fibers or more recently to dif
ferentiate fibers from untreated (control) and fungus-treated wood chi
ps. Aspen or loblolly pine wood chips were treated with white-rot fung
i under different experimental conditions in static-bed bioreactors fo
r two or four weeks. At harvest, control and fungus-treated chips were
refined through a single-disk mechanical refiner and then evaluated f
or fiber staining characteristics and the energy consumption during re
fining. Fibers obtained from control pulps stained a deep blue, wherea
s those obtained from different biopulps showed different intensities
of yellow. The yellowing of biopulp fibers correlated very well with e
nergy savings. The results demonstrate that the Simons staining method
can accurately predict appreciable energy savings during biomechanica
l pulping and therefore can be used as a rapid screening technique to
optimize the biopulping process.