Rheological behaviour of baker's yeast suspensions

By using a few rheometrical instruments (such as a conventional rotational viscometer equipped with a double couette sensor system. a dynamic stress r heometer with cylindrical and plate-and-cone geometry, and Cannon-Fenske ca pillary viscometers), it was possible to assess that yeast suspensions in t he range 25-200 kg m(-3) behaved as Newtonian liquids. In fact, their dynam ic viscosity (as determined under shear flow, oscillatory flow and creep) p ractically coincided with that determined using capillary viscometers. The relative viscosity of these suspensions at 5 degrees C was then correlated to the yeast volumetric fraction (phi) by means of the Krieger equation, wh ile the effect of temperature on viscosity was better described by using a power-law model rather than the Arrhenius relationship, its empirical param eters being dependent on yeast concentration. (C) 2000 Elsevier Science Ltd . All rights reserved.