ABSTRACT
A well-designed viscometer must be capable of providing
readings that can be converted to shear rate (_, sec-1) and shear stress (s, Pa), and allow for the recording of the readings so that time-dependent flow behavior can be stu-
died. In the case of low-viscosity foods, the shear stresses
will be low in magnitude so that instruments that minimize
friction by the use of air bearings are preferable. The flow
in the selected geometry should be steady, laminar and
fully developed, and the temperature of the test fluid
should be maintained uniform.[1]
VISCOMETER GEOMETRIES
For foods that exhibit Newtonian behavior, viscometers that
operate at a single average shear rate, such as a glass capil-
lary, are acceptable. A glass capillary dilution (Ubbelohde)
viscometer is shown in Fig. 1. This viscometer is especially
useful for determining the intrinsic viscosity of a food poly-
mer:[1] 1) A measured volume is loaded through tubeG into
the reservoir J; 2) The viscometer is placed in a vertical
orientation in a constant temperature bath; 3) Tube B is
closed with a finger and suction is applied at A until the
test fluid reaches the center of bulb C, suction at A is
removed, and the finger from tube B is removed and imme-
diately placed over tube A; 4) After removing finger from
TubeA, the efflux time, t for the liquidmeniscus to pass from
D to mark F is measured to within 0.1 second. To ensure
reproducible results, steps 3 and 4 should be repeated.
