Updated March 2000
VISCOSITY
Viscosity exists as both Newtonian and Nonnewtonian fluids. This can be reviewed
by looking at the graphs which shows the interaction
of stress and strain.
Newtonian Liquids
A Newtonian liquid is a liquid for which a graph of shear stress aginst rate of
shear is a straight line. The proportionality constant is called the coefficient
of viscosity. The shorthand symbol is "N", and the mdoel a dash pot which is a
convenient way of visualizing an ideal liquid. It is a container filled with liquid
through which a plunger can be pushed up and down. The Newtonain liquid has no
elastic properties but is incompressible, isotropic, structureless, and, like
the Hooke solid, does not exist in reality.
Non-Newtonian Liquids
NonNewtonian fluids are much more common in foods.
| Characteristic |
Time independent
(steady state) |
Time dependent |
| Thinning |
Pseudoplasticity |
Thixotropy |
| Thickening |
Dilatancy |
Rheopexy |
These terms are the result of historical accident and have no theoretical
significance beyond the type of flow curve. Dilatant liquids do not necessarily
dilate and there is nothing 'pseudo' about pseudoplasticity. References
- Charm, S. 1960. Viscosity of non-Newtonian food materials. Food Research
25:351-362.
- Crockford, H.D. and S.B. Knight. 1950. Fundamentals of Physical Chemistry
for Premedical Students. pp. 54-58.
- Henig, Y. and C.H. Mannheim. 1971. Drum drying of tomato concentrate.
Food Technology 25:59.
- Jacobs, M.B. 1958. Chemical Analysis of Foods and Food Products. pp. 83-87.
- Lauffer, M.A. 1942. Experimental facts pertaining to the relationships
between viscosity, molecular size, and molecular shape. Chem. Rev. 31:561-586.
- Miers, J.C., D.W. Sanshuck, M.D. Nutting, and J. Wanger. 1970. Consistency
of tomato products. Food Technology 24:1189.
- Rao, M.A., H.J. Cooley, and A.A. Vitali. 1984. Flow properties of concentrated
juices at low temperatures. Food Technology 38(3): 113.
- Rao, M.A. 1987March. Predicting the flow properties of food suspensions
of plant origin. Food Technology 41: 85.
- Scaizo, A.M. and R.W. Dickerson. 1970. The viscosity of egg and egg products.
Food Technology 24:1189.
Updated and copyrighted ZoeAnn Holmes 2000. Send mail to Food
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