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VISCOSITY CHARACTERIZATION OF A COMMERCIAL YOGURT AT 5C USING A CUP IN BOB AND A VANE GEOMETRY OVER A WIDE SHEAR RATE RANGE (10 −5 S −1 ‐10 3 s −1 )
Author(s) -
GERAGHTY RICHARD,
BUTLER FRANCIS
Publication year - 1999
Publication title -
journal of food process engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 45
eISSN - 1745-4530
pISSN - 0145-8876
DOI - 10.1111/j.1745-4530.1999.tb00467.x
Subject(s) - rheology , shear rate , viscosity , shear stress , shear (geology) , creep , thermodynamics , slip (aerodynamics) , materials science , chemistry , geometry , mechanics , composite material , physics , mathematics
Equilibrium viscosity data at 5C, over a wide shear rate range (10 −5 s −1 ‐10 3 s −1 ), are presented for a typical commercially available stirred yogurt. A bob in cup and a vane in cup geometry were used in the work. The vane was manufactured to the same outer dimensions as the bob. A series of constant shear stress creep tests was performed, ranging from 2 Pa to 60 Pa. Equilibrium shear rate values were found for each shear stress. Equilibrium viscosity data obtained with both geometries were of the same order of magnitude. This indicated that slip (wall depletion) effects were not significant with the bob in cup geometry used in the study. Application of existing rheological models showed that the equilibrium viscosity behavior of yogurt may be described using either a power‐law of the form or the Cross equation The Cross model better predicted the almost constant viscosities observed at low shear stresses.