Filamentous growth morphology of T. reesei results in a viscous broth rheology that affects oxygen mass transfer rate and changes the broth from a Newtonian mixture to a non-Newtonian mixture over periods of cellulolytic enzyme production. With increasing viscosity, power input requirements increase to achieve the same level of mixing. The increase in the viscosity increases the bubble size and hence reduces the bubble residence time in the fermenter and decreases the mass transfer coefficient. Enzyme and extracellular protein levels were significantly affected at lower (0.5 vvm) and higher (1.5 vvm) oxygen saturation levels and at lower (130 rpm) and higher (400 rpm) agitation levels (Schaffner and Toledo 1992). The change in morphology of T. reesei affects xylanase production at lower aeration (below 10% oxygen saturation level). In addition, xylanase production is sensitive to shear stress at power agitation (Weber and Agblevor 2005).