The conditions of the filter paper activity (FPA) assay were standardized f
or solid substrate fermentation (SSF). The FPA is a relative measure of the
overall cellulose hydrolysing capacity of microbial cellulase preparations
, thus reliable and comparable data may be obtained only under standardized
conditions. The standardization developed for submerged fermentation (SF)
cannot be translated directly to SSF. In SSF, the FPA is strongly dependent
on the extraction volume and on the dilution of the enzyme in the assay. T
he optimal extraction volume was substrate dependent in SSF of corn fiber,
spent brewing grains and wheat straw for cellulase production by Trichoderm
a reesei Rut C30. Other cellulolytic enzyme assays (endoglucanase, beta-glu
cosidase and xylanase) were much less sensitive to the extraction volume.